SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES ? NUMBER 12
An Atlas of Volcanic Ash
Grant Heiken
APR 18
SMITHSONIAN INSTITUTION PRESS
City of Washington
1974
ABSTRACT
Heiken, Grant. An Atlas of Volcanic Ash. Smithsonian Contributions to theEarth Sciences, number 12, 101 pages, 15 figures, 33 plates, 3 tables, 1974.?
Volcanic ash samples collected from a variety of recent eruptions were studied,using petrography, chemical analyses, and scanning electron microscopy to
characterize each ash type and to relate ash morphology to magma compositionand eruption type.
The ashes are best placed into two broad genetic categories: magmatic and
hydrovolcanic (phreatomagmatic). Ashes from magmatic eruptions are formed
when expanding gases in the magma form a froth that loses its coherence as
it approaches the ground surface. During hydrovolcanic eruptions, the magma
is chilled on contact with ground or surface waters, resulting in violent steam
eruptions. Within these two genetic categories, ashes from different magma
types can be characterized. The "pigeon hole" classification used here is for
convenience; there are eruptions which are driven by both phreatic and mag-
matic gases.
The morphology of ash particles from magmatic eruptions of high-viscosity
magma is governed primarily by vesicle density and shape. The vitric ash par-
ticles are generally angular, vesicular pumiceous fragments, or thin vesicle wall
fragments. The morphology of lithic fragments is dependent on the texture and
mechanical properties of the rock units broken up during the eruption; most
of the samples studied contain equant, angular to subrounded lithic fragments.
Ash particles from eruptions of low-viscosity magmas are mostly droplets;
droplet shape is in part controlled by surface tension, acceleration of the droplets
leaving the vent, and air friction. Shapes range from perfect spheres to a variety
of twisted, elongate droplets, with smooth, fluidal surfaces.
The morphology of ash particles from hydrovolcanic eruptions is controlled
by stresses within the chilled magma which result in fragmentation of the glass
to form small blocky or pyramidal ash particles. Vesicle density and shape play
only a minor role in determining the morphology of these ash particles.
OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded
in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 4983. SERIES COVER
DESIGN: Aerial view of Ulawun Volcano, New Britain.
Library of Congress Cataloging in Publication Data
Heiken, Grant
An atlas of volcanic ash.
(Smithsonian contributions to the earth sciences, no. 12)
1. Volcanic ash, tuff, etc. I. Title. II. Series: Smithsonian Institution. Smithsonian contribu-
tions to the earth sciences, no. 12.
QE1.227 no. 12 [QE461] 552'.2 73-13519
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $2.00
Contents
Page
Introduction 1
Ash Formation 1
Magmatic Eruptions 1
Hydrovolcanic (Phreatomagmatic) Eruptions 2
Acknowledgments 2
Magmatic Eruptions 3
Ash of Basaltic Composition 3
Pacaya, Guatemala 3
Fuego, Guatemala 3
Cerro Negro, Nicaragua . 3
Etna, Italy 4
Deception Island, Antarctica 4
Kilauea Iki, Hawaii 4
Kilauea, Hawaii (reticulite) 5
Aloi-Alae Vent Area, Hawaii 5
Oshima, Japan 5
Taal, Philippines 5
Ashlike Particles of Basaltic Composition 6
Makaopuhi Pele's Hair 6
Flow Top Glass-Kilauea Crater, Hawaii 6
Ash of Andesitic to Rhyolitic Composition 7
Ruapehu, New Zealand 7
Merapi, Indonesia 7
Mayon, Philippines 7
Krakatau, Sunda Straits, Indonesia 8
Santiaguito, Guatemala 8
Katmai, Alaska 8
Mazama (Crater Lake) Ash 9
Ash of Carbonatite Composition 9
Oldoinyo Lengai, Tanzania 9
Hydrovolcanic (Phreatomagmatic) Eruptions 9
Ash of Basaltic Composition 9
Capelinhos, Azore Islands 9
Surtsey, Vestmann Islands, Iceland 10
Taal, Philippines 10
Table Rock, Oregon 10
Kilauea, Hawaii 10
Ash of Rhyolitic Composition . 11
Panum Crater, California 11
Sugarloaf, San Francisco Mountains, Arizona 11
Ash from Littoral Steam Eruptions 11
Basaltic Composition 12
Puu Hou Littoral Cones, Hawaii 12
Hi
Page
Sand Hills Littoral Cone, Hawaii (historic) 12
Ash-Size Particles of Meteorite Impact and High-Energy
Explosion Origin 12
Ries Basin, Germany . 12
Dial-Pack Explosion, Alberta, Canada 13
Conclusions and Summary 13
Literature Cited 13
Appendices 15
Appendix 1: Chemistry of the Volcanic Ashes Studied for This
Report 15
Appendix 2: Gas Release Study of Selected Volcanic Ashes
(by Everett K. Gibson, Jr.) 15
IV
An Atlas of Volcanic Ash
Grant Heiken
Introduction
Morphologic descriptions of volcanic ash par-
ticles are present in the literature, mostly as thin-
section descriptions. Shard shapes are rarely de-
scribed as three-dimensional forms; analyses of this
sort are generally restricted to bombs and other
coarse-grained volcanic ejecta (Wentworth, 1938).
Furthermore, only recently, Walker and Croasdale
(1972) and Heiken (1972) have related ash mor-
phology to the composition of the magma or type
of eruption.
The purpose of this study was to analyze a large
variety of volcanic ash samples, using most stand-
ard laboratory techniques, to determine if there
is a relation between the type of eruption, the
magma composition, and the ash particle mor-
phology.
The following items were determined for each
ash sample studied: the locality, eruption type,
type (s) of volcanic features associated with this
ash, bulk chemistry (in most cases), and modal
analysis (grain counts, rather than point counts,
were made of each ash thin section). Petrographic
and scanning electron photomicrographs (SEM)
were taken to characterize the ash morphology. The
chemical analyses and size analyses of ashes studied
here are summarized in Appendices 1 and 2.
Ash names used here are based on the size classi-
fication of volcaniclastic fragments by Fisher (1961)
(Plate 1A), used in conjunction with a composi-
tional classification set up by Cook (1965) (Plate
IB).
For brevity, each petrographic mode is summar-
Grant Heiken, Geology Branch, NASA, Johnson Space Center,
Houston, Texas 77058.
ized in the text with percentages of glass, tachylite,
crystal fraction, lithic fragments.
This is an expanded version of a paper by
Heiken (1972) on the morphology and petrography
of volcanic ash. For a review of the mechanisms
of ash formation and introductory text for each
section of this atlas, see the paper by Heiken; there
is, however, some necessary duplication between
the two papers.
It is hoped that the reader using this catalog as
a reference can, on the basis of petrography and
ash morphology, infer the genesis of an ash sample.
This catalog is potentially useful when working
with isolated ash beds found on land, in deep-sea
cores, and perhaps in lunar soil. Most of the mor-
phologic features studied here with scanning elec-
tron microscope can be identified with standard
microscopes.
ASH FORMATION
There are two basic mechanisms of ash forma-
tion: (1) by exsolution and expansion of gases in
a magma, resulting in the froth losing its coher-
ence as it approaches the ground surface (mag-
matic eruptions), and (2) by chilling of a magma
rising toward the ground surface on contact with
ground or surface water (hydrovolcanic or phreato-
magmatic eruptions).
MAGMATIC ERUPTIONS
The basis for understanding the first type of ash
formation was set forth in a paper by J. Verhoogen
(1951):
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
Ash formation is believed to depend especially on the
kinetics of gas evolution, the crucial factor being the number
of bubbles per unit volume which may be present at a certain
time. Initial water content of the magma, degree of over-
saturation developed, cause of oversaturation, viscosity, sur-
face tension, temperature, depth, nature and amount of
suspended crystals, are among the factors which determine
the rate and mode of gas evolution, without much indication
of any of these being more important than the others. . . .
Differences in volcanic behavior, as between Pelean and Vul-
canian explosions, formation of pahoehoe, quiet outflow and
explosion of pumice, are not necessarily related to one or
even two variables only. It is more probable that at least a
half dozen variables should be required for an adequate
analysis, and that such differences as are observed depend on
a combination of a large number of apparently insignificant,
or at least not very obvious, factors.
The shape of glassy ash particles is mostly depend-
ent on bubble (vesicle) shape and density, which
is, in turn, dependent on the variables outlined
by Verhoogen.
Explosive eruptions of a magma with a low vis-
cosity, caused by expanding, coalescing gas bubbles
at the surface, throw out sprays of droplets or
pasty clots. Droplet shapes are controlled mainly
by the effect of surface tension and deformation
of the droplet by acceleration and air resistance.
In this case, the vesicle shapes within each droplet
are partly controlled by the external forces listed.
Ash from magmas with slightly higher viscosities,
such as basaltic magma with abundant phenocrysts
or some andesitic magmas, is composed of scoria
with few fluidal shapes (there is a small droplet
component).
The morphology of ash eruptions of high-
viscosity magma (rhyolitic, dacitic, and some an-
desitic magmas) is entirely dependent on the shape
of vesicles in the rising magma before disintegra-
tion. The concavities, troughs, and tubes on grain
surfaces are broken vesicle walls. Elongate grain
shapes are controlled by elongate (pipe) vesicles
and equant grain shapes by equant, undeformed
vesicles. Flat or slightly curved platy shards are
from broken vesicle walls. Only rarely are there
scattered droplets of silicic ash from magmas with
viscosities low enough to assume a fluidal shape.
The shape of lithic fragments in ash should be
controlled by the mechanical properties of the wall
rock, broken up by spalling or explosive expansion
of gases in the magma as it approaches the surface.
Generally, most lithic fragments of ash size are
equant and slightly rounded, indicating some pos-
sible rounding by particles grinding against each
other during the eruption.
HYDROVOLCANIC (PHREATOMAGMATIC) ERUPTIONS
Vesicle shape and density play only a minor role
in the determination of grain shape in hydrovol-
canic (phreatomagmatic) eruptions. In this sort
of eruption, the rising magma is quickly cooled
on contact with ground or surface water. Stresses
within the "quenched" magma cause fragmenta-
tion into small blockly or pyramidal glass particles
(Walker and Croasdale, 1972, and Heiken, 1971
and 1972). In many instances, it appears that the
chilling occurs before much of the gas is released
from the magma, explaining the low vesicularities
characteristic of hyaloclastic ashes. (Hyaloclastic is
a term coined by Rittman [1962] to describe ashes
formed by the chilling-fracturing process described.)
This atlas is split into the two basic categories
of magmatic and hydrovolcanic, with subdivisions
based on magma type.
ACKNOWLEDGMENTS
I want to thank the following people for pro-
viding very useful information and ash samples:
W. I. Rose, Dartmouth University; Oliver Kola,
Anchorage, Alaska; Arturo Alcarez, Phillippine
Commission on Volcanology; K. R. Everett, Insti-
tute of Polar Studies, Ohio State University; D.
Hadikusomo, Geological Survey of Indonesia; Gary
Lofgren, Fred Horz, and M. C. McEwen, NASA
Manned Spacecraft Center; J. B, Dawson, Univer-
sity of St. Andrews, Scotland; Mike Sheridan, Ari-
zona State University; S. Thorarinsson, Museum
of Natural History of Iceland; the Portuguese Geo-
logical Survey; David Roddy, U.S. Geological Sur-
vey; J. Healy, and C. P. Wood, New Zealand
Geological Survey; W. Melson, Smithsonian Insti-
tution; Roald Fryxell of Washington State Uni-
versity, R. Funiciello of the University of Rome,
and Floyd McCoy, Woods Hole Oceanographic
Institute. Special thanks go to R. V. Fisher, Uni-
versity of California, for providing abundant
samples from Hawaii and for training in studies
of pyroclastic rocks. Beverly Atkinson and Liz Alley
efficiently typed the manuscript, David McKay,
Tom Simkin, R. Fiske and W. Phinney criticized
NUMBER 12
the manuscript, and Sue Montgomery and Don
Ryan edited it. Members of the Federacion
Andismo, especially Arturo Veliz, helped greatly
in supporting the sampling effort in Guatemala.
Training for use of the scanning electron micro-
scope was generously provided by David S. McKay
and Garth Ladle of the NASA Manned Spacecraft
Center.
Magmatic Eruptions
ASH OF BASALTIC COMPOSITION
PACAYA, GUATEMALA.?1968 eruption. The 1968
eruption occurred at one of two young cinder cones
at the southwest peak, located 40 km south-
southwest of Guatemala City (for a review of
activity see Stoiber and Rose, 1970). There is
mostly strombolian type of activity at this volcano.
This sample is from the surface, 1 km west of the
vent.
Petrography: This vitric ash sample consists of
mostly light-brown, clear glass (sideromelane) drop-
lets, or broken droplets with a thin dark-brown
skin. There are phenocrysts of olivine, pyroxene,
and feldspar (~An70) in many of the droplets.
(97:0:3:0)
Morphology: The ash (Plate 2) consists of mostly
broken glass droplets. In contrast to the glass
ovoids, spheres, and Pele's hair formed from melts
of very low viscosity (such as those at Kilauea),
the strombolian activity and lava fountains at
Pacaya produced irregularly shaped droplets with
botryoidal surfaces.
Most vitric ash grains from Pacaya are equant
and contain ovoid or spherical vesicles. Present in
minor proportions are slightly elongate grains that
may be twisted about the long axis. The elongate
grains contain irregular pipe vesicles, oriented
parallel to the long axis of the grain.
The botryoidal glass droplet surfaces have a
smooth skin that can be seen in thin section. The
10- to 50-micron-thick skin is formed rapidly after
ejection of the droplet from the vent. It is broken
or deformed by collapsed vesicles located near the
outer edges of the droplet (Plate 2F). Droplets
broken after cooling do not have a skin along the
broken surface. The broken grain surfaces are
irregular, with sharp, angular corners.
FUEGO, GUATEMALA.?Fuego is a strato-volcano
consisting of interbedded flows and pyroclastics of
andesitic to basaltic composition. These samples
are from the eruption of August 1966, when ash
clouds reached elevations of approximately 12,000 m
(Stoiber and Rose, 1970). The sample is from the
surface, 3 km north of the active vent, on Acate-
nango, another volcano adjacent to Fuego.
Petrography: This vitric ash is of basaltic com-
position. The tachylite occurs as black opaque
grains that are submicrocrystalline basalts. It is
often associated with sideromelane, which is true
basaltic glass. (72:9:19:0)
Morphology: The ash from Fuego (Plate 3) is
similar to the Pacaya ash. It is composed mostly
of broken sideromelane droplets, with lesser
amounts of tachylite and mineral fragments. In
contrast to the Pacaya ash, glass droplets produced
in the violent ash eruption are all broken; none
retain the fluidal grain shapes characteristic of
droplets from Pacaya. Most of the particles are
equant to slightly elongate, with hackly, irregular
grain surfaces. Original droplet surfaces are only
rarely preserved as patches of smooth skin (Plate
3A). Tachylite and basalt fragments have extremely
hackly, irregular surfaces (Plate 3E).
Droplets were probably broken by grinding
within the upper part of the vent or eruption
cloud, or by continued expansion of vesicle gases.
It is also possible that only a few droplets with
perfect fluidal shapes were formed initially. Com-
minuted, irregularly shaped ash fragments are pro-
duced in large-scale ash eruptions of andesitic or
basaltic magmas.
CERRO NEGRO, NICARAGUA.?1968 eruption. Cerro
Negro is the youngest of four clustered cinder
cones along a north-south fault line in the Central
Marabios Range, Nicaragua. The 1968 eruption
ejected abundant blocks and ash, and an ash cloud
rose to an altitude of several thousand meters. A
flank eruption was characterized by lava fountain-
ing and an ash flow. The lavas and ejecta are of
olivine basalt. The exact sample location is not
known by the author.
Petrography: The vitric ash consists of mostly
irregularly shaped, broken droplets of sideromelane
and tachylite that contain abundant phenocrysts
of clinopyroxene (augite) and plagioclase. There
are grains of sideromelane containing patches of
submicrocrystalline tachylite. (55:30:15:0)
Morphology: The grain morphology is similar
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
to that of the ashes from Pacaya?consists of a
mixture of broken sideromelane droplets and tachy-
lite fragments (Plate 4). The droplets have smooth
botryoidal or lumpy outer surfaces, broken by de-
pressions over vesicles in outer droplet edges
(Plates 4A, 4C). Depressions with smooth edges
were formed when the outermost vesicles broke
while the droplet was still partly fluid (Plate 4A).
The sharp-rimmed depressions were formed when
thin vesicle walls were broken after the droplet
had cooled (Plate 4c). The irregular droplets and
broken droplets are associated with strombolian
eruptions (mixed ash eruptions and lava foun-
taining).
ETNA, ITALY.?Etna is a broad stratovolcano,
with multiple vents and abundant cinder cones
near the summit and on the slopes. This ash is
from accelerated Strombolian activity at cinder
cones near the observatory in April 1971. This ash
sample is from the First Cable Car Station
(2400 m).
Petrography: This is a lithic-vitric ash, consist-
ing of mostly broken porphyritic, pale brown
(sideromelane) droplets, with very low vesiculari-
ties (Plate 5E, F). Only a small percentage of the
droplets have a few spherical vesicles. There are
dark reddish-brown glass fragments, which are
probably an oxidized form of the sideromelane.
Some of the glass grains are partly devitrified, with
small brown bundles of spherulites.
The tachylite grains are porphyritic, equant to
elongate grains with low vesicularity. Included in
the crystal fraction are euhedral plagioclase crys-
tals (length 0.15 mm), many of which exhibit
oscillatory zoning. In lesser amounts is pale green
augite, olivine, and porphyritic basalt fragments
exhibiting an equigranular groundmass. (59:28:
9.5:3.5)
Morphology: The following forms are evident
from the SEM Photomicrographs:
1. Equant, blocky, nonvesicular fragments with
hackly grain surfaces, which are the tachylite
grains. Some of these grains have been rounded.
At higher magnification, many of these grains ex-
hibit diktytaxitic texture, with an open, meshlike
network of feldspar (?) grains, l^i?2|* long and
O.Sjx wide. Voids between the crystals occupy 30
to 50 percent of the rock by volume (Plate 5B, C).
2. Angular, broken droplets exhibiting low ve-
sicularity. The shards are mostly blocky fragments,
with scalloped edges where the grain surface con-
sists of broken vesicle walls (30- to 150-micron-
diameter vesicles). Fracture surfaces are smooth
and sometimes conchoidal (Plate 5D).
3. There are a few agglutinates in the sample
(droplets welded together as irregular, botryoidal
grains) (Plate 5A).
4. Clinopyroxene and feldspar grains.
DECEPTION ISLAND, ANTARCTICA.?1969 eruption.
Deception Island, a volcanic island composed of
tuff rings and cinder cones, is located off Graham
Land, Antarctica, near the South Shetland Islands.
This sample of cinders and ash is from the erup-
tion that began on 21 February 1969. The eruption
was characterized by the ejection of ash, scoria, and
bombs. The exact location of the sample is not
known. Both magmatic and hydrovolcanic activity
occurred on the island during this eruption.
Petrography: The vitric ash consists of mostly
irregular, broken droplets of sideromelane or tachy-
lite, each containing feldspar microlites and some
olivine phenocrysts. (64.5:35:0:0.5)
Morphology: The ash consists of equant to
moderately elongate sideromelane and tachylite
grains and is similar to the ashes from Fuego,
Guatemala. Most of the ash fragments have rough,
irregular surfaces (Plate 6). Smooth droplet sur-
faces characteristic of ashes from lava fountains
are rare.
A few ash grains exhibit a diktytaxitic texture,
which consists of an open network of feldspar
microlites coated with a thin layer of glass. This
texture may have been formed by fluid draining
from between feldspar microlites or by the growth
of irregular vesicles between the crystals in the
melt.
KILAUEA IKL, HAWAII.?Kilauea Iki is a pit crater
adjacent to the eastern edge of the Kilauea Caldera.
The vitric ash is from lava fountaining that oc-
curred in 1959. The samples were collected 2100 m
southwest of the vent.
Petrography: The sideromelane droplets con-
tain few or no phenocrysts or microlites. The mode
is 100 percent sideromelane droplets. (100:0:0:0)
Morphology: Lava fountaining produced an
abundance of unbroken glass droplets and Pele's
hair (long, thin strands of glass) in the ash-size
fraction (Plates 7, 8). Glass spheres and ovoids were
droplets of melt in which surface tension had a
greater effect than either air resistance or accelera-
NUMBER 12
tion of the droplets from the vent. Vesicles within
the spheres are nearly always spherical. Nearly all
the droplets have a 10- to 50-micron-thick skin.
The skin is broken by small-scale contraction joints
oriented perpendicular to the droplet surface. In
places where the joints separated during expansion
of the droplet, the cracks were penetrated by fluid
from the droplet interior (Plate 7F). Droplet sur-
faces were generally broken over some of the outer-
most vesicles (Plates 7B, 7C, 8D). Some are smooth,
lacking these surface depressions.
Long, thin strands of glass (Pele's hair) are
formed by the acceleration of droplets from the
vent, possibly aided by gas streaming by a droplet
or fluid clot. The initial stages in the formation
of Pele's hair begin with the development of taper-
ing tails on droplets (Plate 7c). Vesicles within the
glass strands are drawn into long, pipelike shapes
(7G-L).
The abundance of spherical and ovoid droplets
in the Kilauea ashes is a characteristic of ashes
from Hawaiian eruptions of low-viscosity magmas.
This is in contrast with ashes from the strombo-
lian eruptions of Central American volcanoes
(Pacaya, Fuego, Cerro Negro), where spherical and
ovoid droplets are rare.
KILAUEA, HAWAII (reticulite).?This sample of
reticulite ash (also known as limu or thread-lace
scoria) was taken from the reticulite pumice layer
near the Hawaii Volcano Observatory; the first
volcaniclastic unit above flows on the rim of the
crater. It is a light-brown glass of basaltic compo-
sition that was blown downwind from the lava
fountaining of a low-viscosity, high-temperature
melt.
Petrography: This vitric ash is composed of a
sideromelane froth, lacking phenocrysts or micro-
lites of any kind. The mode is 100 percent sidero-
melane. (100:0:0:0)
Morphology: The continued growth of vesicles
in a basaltic magma with very low viscosity
(Kilauea) produces an open network or froth.
The froth, called reticulite, consists of a lattice-
shaped network of triangular glass rods (Plate 9).
The low density of this ejecta allows the bits of
froth to drift for some distance in the wind.
ALOI-ALAE VENT AREA, HAWAII.?The ash is from
lava fountaining in the Aloi-Alae craters area, on
the Chain of Craters Road (Puna Rift Zone), in
December 1969. These are pit craters on the flank
of a large shield volcano. The sample was collected
approximately 1 km west of Alae Crater.
Petrography: The vitric ash consists of Pele's
hair, spheres, and ovoids. The mode is 100 percent
sideromelane droplets and broken droplets.
(100:0:0:0)
Morphology: The ash, from large-scale lava
fountaining, is nearly identical to the Kilauea
ashes (Plate 10).
OSHIMA, JAPAN.?Oshima is a polygenetic shield
volcano consisting of basaltic ash and tholeiitic
basalt flows. There is a central main vent with
caldera and 40 parasitic cones on the shield.
This sample is from the "Sj" layer (midslope on
the main cone, a unit approximately 0-5 m thick),
which is an accretionary lapilli tuff. The age is
650 ? 150 years B.P. (Nakamura, 1964). The ash
is possibly from a strombolian-type eruption.
Petrography: This lithic-vitric ash consists of
mostly broken sideromelane and tachylite droplets
or agglutinates (several droplets welded together).
The lithic component consists of equant fragments
of aphanitic basalt. There is a trace of pyroxene
phenocrysts, not in vitric or lithic fragments.
(55:21:Tr:24)
Morphology: The ash consists of irregular,
equant sideromelane and tachylite fragments (Plate
11). Most are broken fragments. Botryoidal grain
surfaces are characteristic of the sideromelane
droplets. Included in the ash are basalt fragments,
exhibiting irregular, hackly surfaces. This sample
contains a number of agglutinates, that is, sidero-
melane and tachylite droplets welded to each other
or to lithic and mineral fragments.
The type of eruption was not observed. Because
of the similarity of the ash to the Central Ameri-
can basaltic ashes, it is possible that it was ejected
during a strombolian eruption.
TAAL, PHILIPPINES.?1968. Volcano Island, in
Lake Taal, Philippines, consists of overlapping tuff
rings and cinder cones. An eruption beginning in
1965 was hydrovolcanic (phreatomagmatic), caused
by lake water coming into contact with rising
magma. In the later eruptive phases, as the tuff
ring was built, water no longer had access to the
craters. After this, a cinder cone was formed by
ash eruptions and lava fountaining. This basaltic
ash sample is from the cinder cone.
Petrography: The vitric ash consists of mostly
sideromelane droplets that contain 10 to 30 percent
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
microlites of feldspar and some small olivine pheno-
crysts. There are a few equant basalt fragments and
feldspar crystals in the ash. (96.6:0:2.5:0.8)
Morphology: The ash, produced during inter-
mittent ash eruptions and lava fountaining (strom-
bolian), consists of mostly sideromelane droplets,
broken droplets, and glass-coated phenocrysts
(Plate 12). There are a few imperfect spheres
and ovoids in the ash (Plate 12E). Most of the
broken droplets are tabular or flattened, with long
axes of flattened vesicles oriented parallel to long
axes of the grains. Droplet surfaces are lumpy or
botryoidal (Plates 12D, 12F, 12I). The more elon-
gate droplets are sometimes twisted about the long
axis. The ends may taper to a point but are gen-
erally broken (Plates 12A, 12B). Tachylite grains
are similar in shape to the tabular, broken sidero-
melane droplets but have rough, pitted surfaces.
ASHLIKE PARTICLES OF BASALTIC COMPOSITION
MAKAOPUHI PELE'S HAIR.?Lava flowing from
Alae Crater, Hawaii, into the Makaopuhi pit crater
forms lava falls. As the lava falls hit irregularities
in the crater wall, irregular streams of lava arc
out from the falls. Strong whirlwinds generated at
the crater edge pick up strands of glass and carry
them out of the crater, along with thin glass sheets.
This sample was collected on the north rim of
Makaopuhi Crater, within 30 m of the lava falls.
Petrography: This is a vitric "ash," consisting
of thin strands of clear, pale brown glass. The glass
is homogeneous, with 2 to 5 percent clots of 0.02-
0.6 mm diameter, olivine crystals; there are lumps
in the glass strands over the phenocryst clots (Plates
13c, E, F). Some of the olivine crystals have ovoid
bubbles. There is a trace of 0.2-0.3 mm long pla-
gioclase laths.
In contrast with other forms of Pele's hair, the
skin is very thin and poorly developed. Hair
diameters range from 15[x-500n; 81 percent of the
hairs are vesicular and 19 percent are nonvesicular;
the vesicular hairs have about 10 percent vesicu-
larity. Most of the <50|x diameter hairs are non-
vesicular, with few exceptions.
Morphology: Two types of pele's hair are
present in this sample: (1) Ribbed strands of glass
(ribs parallel the long axis of the strand); one
example characteristic of this form is a 250-micron-
diameter strand which has one 165-micron-wide
rib flanked by ribs ll[i-25ji wide (Plate 13c, F).
The grain surface is extremely smooth. In a few
places on the strand, where the surface is broken,
the ribs overlie elongate vesicles. In one case, the
outer vesicle walls of an elongate vesicle under a
strand are l|x-3u thick. There are some 1- to
2-micron-diameter glass strands welded to the sur-
face of the larger grains. (2) Cylindrical or nearly
cylindrical strands with very smooth surfaces (Plate
13A, B).
These pele's hairs are nearly impossible to sep-
arate from those formed during lava fountaining
on the basis of petrography and morphology.
FLOW TOP GLASS-KILAUEA CRATER, HAWAII.?
These glass fragments were formed by the mechani-
cal disintegration of the glassy crust of the Sep-
tember 1971 pahoehoe flow into the north end of
Kilauea Crater. On fresh pahoehoe flows, the highly
vesicular skin breaks off only minutes after cooling,
to form vesicular platelets with flattened vesicles.
The platelets, which are from 1-20 cm long, are
broken up during movement by wind and water.
The small fragments are carried off by the wind.
This is not an ash, but I have included it because
the windblown fragments could be easily mixed
into ash deposits around a volcano.
Petrography: This sample consists of pale
brown homogeneous glass (sideromelane), with
about 5 percent phenocrysts and 5 to 10 percent
spherulites in early growth stages (Plate 14B). The
olivine phenocrysts are 0.4?0.2 mm long. Many
contain abundant ovoid to elongate bubbles; long
axes of the bubbles are parallel to the long axis
of each crystal. Feldspar phenocrysts, 0.12-0.13 mm
long, have thin "haloes" of spherulites. Smaller
feldspar crystals have spherulitic prongs at both
ends. Other sheaf spherulites are present singly
or in clusters throughout the glass. Each cluster
has a brown "halo."
Morphology: The larger plates, when viewed
from the top, have a rough, ropy, flattened surface,
with superimposed, collapsed vesicles. From the
bottom, the surface consists of smooth, curved
vesicle walls, with vesicles 2 mm-2 cm in diameter
(Plate 14A).
Ash-size particles formed by the disintegration
of the glassy crust consist of I- or T-shaped vesicle-
wall fragments. Vesicle walls are smooth except
for some shallow depressions and lumps (possibly
over phenocrysts). The fracture surfaces are hackly
NUMBER 12
to conchoidal. Vesicle-wall fragments are 0.1-1 mm
thick; no smaller vesicles are visible in the walls
(Plate 14A).
These could be confused with a component of
littoral cone ash deposits, which are formed also
by the disintegration of presolidified pahoehoe
crusts.
ASH OF ANDESITIC TO RHYOLITIC COMPOSITION
RUAPEHU, NEW ZEALAND.?June 1969 eruption.
The ash was erupted in an initial burst that may
have spread ash-flow ash in several directions on
the steeper slopes of the volcano, with subsequent
airfall material drifting farther northwest. Later
came the explosive eruption that threw out large
masses of crateral material, including boulders and
mud, as well as some of the crater-lake water. This,
combined with snow melted by the hot blast,
formed a number of lahars which carried ash down
into several of the outward-draining streams
(Healy, written communication, 1970). It is pos-
sible that there might not have been an ashflow
at all, but only mudflows as the eruption emptied
the crater lake and the lake sediments. Wood (writ-
ten communication, 1972) has examined the "ash-
flow" material and has evidence that most of this
tephra is from detritus and lake-derived minerals.
Gypsum is abundant in these samples.
The sample was collected at the south margin
of Whangaehu Glacier, approximately 350 m north-
east from the center of the crater lake. The sample
may have been part of a nu?e ardente or partly
deposited by lahar (Healy, 1970, personal com-
munication).
Petrography: The lithic-vitric ash consists of
fragments of porphyritic andesite; mudstone;
medium-crystalline pyroxene-hypersthene andesite;
tachylite; feldspar-rich andesite; crystals of ande-
sine, hypersthene, and augite; and fine-grained
colorless glass shards and pumice. Some of the
pumice grains have brownish, oxidized rims.
(12:0:4.3:83.7)
Morphology: Most of the ash consists of equant,
elongate, and pyramidal lithic fragments of an-
desitic composition (Plate 15). The lithic fragments
generally have rough, pitted surfaces; they may
range from the freshly comminuted rock, with
planar fracture surfaces, to grain surfaces rounded
by grinding of particles within the vent or eruption
column.
The vitric component of the ash consists of
equant grains with low vesicularity and spheroidal
ovoid shapes and pumice fragments with elongate
vesicles. Pumice surfaces are very rough, with
bladed edges of closely spaced vesicles exposed at
the surface of each grain. No droplets are present;
the vitric ash grains left the vent as solid pumice
fragments. Most grains are coated with irregular
patches or layers of sublimates, mainly sulfur com-
pounds. Many grains are weathered rock fragments
that may have been from an ash deposit in the
crater from previous eruptions.
This eruption may have been partly hydrovol-
canic and is a mixture of magmatic and hyaloclastic
ashes.
MERAPI, INDONESIA.?The eruption began 10 Oc-
tober 1967, with formation of a lava dome and
nue"es ardentes. In January 1969, eruptive activity
included nuees ardentes, airfall, and secondary
lahars (associated with heavy rains). This is an
airfall sample of andesitic composition. The
exact sample location is not known but is suspected
to be some distance from the vent because of the
well-sorted nature and very fine grain size of the
ash.
Petrography: The sample is a crystal ash, con-
sisting of mostly very small feldspar, orthopyroxene,
and clinopyroxene crystals and angular, colorless
glass shards. The ash is very well sorted.
(35:0:64:1.0)
Morphology: The ash may not be completely
characteristic of ejecta from this eruption. The
exact location is not known, but the extremely fine
grain size indicates that it was probably collected
far enough from the vent to have been sorted by
wind and gravity.
Most of the ash consists of broken, anhedral
feldspar crystals (Plate 16). The remaining portion
consists of very fine-grained, angular, and pointed
glass shards. A few of the shards contain small,
irregularly shaped vesicles. The fine-grained vitric
fragments are probably pieces of thin vesicle walls.
MA YON, PHILIPPINES.?29 May 1968. Mayon is a
symmetrical stratovolcano composed of dominantly
andesitic flows and pyroclastic rocks. This ash is
from an eruption of porphyritic augite-hypersthene
andesite ash in airfall and nue*es ardentes clouds
(Moore and Melson, 1969). There are some accre-
8 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
tionary lapilli in the ejecta. The exact distance
of the sample from the vent is unknown.
Petrography: The crystal-lithic ash consists of
broken crystals of augite, hypersthene, and plagio-
clase; equant andesite fragments; and colorless
glass shards and pumice. Most of the pumice and
some shards have a thin, brown oxidized rim.
(59:0:27.7:13.3)
Morphology: The ash is similar to, but coarser
grained than, the Merapi ash sample and may have
been collected closer to the vent. The vitric com-
ponent is dominant in this sample. As in the
Merapi ash, there is an abundance of thin, elon-
gate, pointed glass shards (Plate 17), the product
of finely comminuted pumice. Larger glassy par-
ticles are curved, being the more complete remnants
of vesicle walls.
Surfaces of grains that are bits of vesicle wall
are smooth and curved. Fractured grain surfaces
are more irregular, exhibiting conchoidal fracture
surfaces. Pumice fragments, with a wide range of
vesicle shapes (generally elongate), are equant to
slightly elongate. The grain shape reflects the
vesicle shapes within it. The ash is probably the
product of disintegration of a plug of viscous, gas-
rich pumice rising in the vent.
KRAKATAU, SUNDA STRAITS, INDONESIA.?I have
included this study as an early example of the
relation of ash type to eruption type and as an
example of a particularly violent eruption. Kraka-
tau was a 200-meter (?)-high volcano that was
destroyed in 1883, leaving a submerged caldera
and three islands (Van Padang, 1951). Activity
began on 21 May 1883, with ash clouds rising to
11 km. The most violent eruptions occurred during
the period of 26-28 August. It is believed that ash
clouds reached heights of 70-80 km (Van Padang,
1951).
Sample Description: I have abstracted this de-
scription from a report on the eruption of Kraka-
tau by J. W. Judd (1888). The ejecta consists of
colorless to dirty grayish-white ash and pumice;
the pumice has irregular vesicles with little knots
of feldspar, pyroxene, and magnetite crystals.
Some of the pumice grains are rounded. Lithic
fragments present in the ejecta were andesitic,
believed to be from the old crater ring.
Judd correctly assumed that the pumice was
formed by the escape of volatiles while the magma
was still viscous. Vitric ash fragments, which make
up most of the ejecta, consist of curved plates and
angular threads which were assumed to have
formed by the explosion or grinding of pumice
fragments against each other. Judd found that the
ash could be simulated by grinding Krakatau
pumice (Plate 18).
SANTIAGUITO, GUATEMALA.?Santiaguito is a
multiple dacite dome, active since 1922. The bulk
of the ash eruptions and nue'es ardentes originate
at the Caliente dome. This ash was airfall from
ash emission occurring on 28 July 1970, and was
collected approximately 1.5 km west of the vent.
Petrography: This lithic ash consists of equant
hyalocrystalline dacite fragments (these could pos-
sibly be classified as vitric, with abundant micro-
lites and phenocrysts), plagioclase (An43), and
quartz crystals. Most vesicles are irregular, flat-
tened ovoids. (0:0:25:75)
Morphology: The most abundant components
in the ash are equant, slightly vesicular, irregularly
shaped, hyalocrystalline dacite fragments (Plate
19). Most grain surfaces are hackly to conchoidal.
The more glassy fragments are slightly more vesic-
ular and have smooth grain surfaces (Plates 19D,
19E). Plagioclase is the most common mineral
component in the ash. Individual phenocrysts are
highly fractured, often breaking along twin planes.
The ash formed during the vesiculation and dis-
integration of the upper part of a growing dacite
dome and flow.
KATMAI, ALASKA.?The sample is from the ash
flows in the Valley of Ten Thousand Smokes, which
were deposited in 1912 by nu?es ardentes from a
center at what is now the Novarupta dome (G.
Lofgren, oral communication). The sample was
collected 20 cm from the bottom of the ash-flow
tuff unit, approximately 17.5 km from Novarupta.
Petrography: The vitric ash is composed of
colorless and brown pumice and shards from a
"mixed" magma (andesitic and rhyolidc composi-
tions). Most of the fragments are elongate, with
the long axis parallel to the thin pipe-shaped
vesicles. Vesicle walls broke up to form flat or
slightly curved, very thin glass shards. (92.4:0:
1.8:6.1)
Morphology: The ash from this eruption con-
sists of small, elongate pumice fragments (Plate
20). The highly vesicular fragments contain elon-
gate, flattened pipe vesicles, separated by very thin
glass walls. Present in lesser amounts are fragments
NUMBER 12
with flattened spheroidal or ellipsoidal vesicles
(Plates 20G, 20H), which grade into the more com-
mon pipe vesicles within the same fragment.
The fine-grained portion of the ash consists of
mostly shards broken from thin vesicle walls. It
consists of flat, curved, and Y-shaped fragments.
The ash was formed by the disintegration of a
plug of rhyolitic magma at or near the surface.
MAZAMA (CRATER LAKE) ASH.?This sample was
collected in Steptoe Canyon, 0.8 km from Stewart
Canyon, Whitman County, Washington. The erup-
tion of Mt. Mazama (Crater Lake), located in
south-central Oregon, consisted of large Plinian
eruptions, with extensive ash fall and ash flows.
The age, determined by C14 methods is 6600 years
B.P. This eruption was not observed, but is in-
cluded here because of the numerous studies of it
(Fryxell, 1963; Williams, 1942; Wilcox, 1965) and
its importance as a stratigraphic marker in the
Pacific Northwest.
Petrography: This is a vitric ash, consisting of
colorless, flat, and curved shards and small pumice
fragments. Pumice fragments are up to 50 microm-
eters long with very angular shapes. Shards l\i-
100[i long, in cross section, have a variety of shapes
including Y-shaped, curved, platelike and flat,
tapered platelets. (100:0:0:0)
Morphology: The 1- to 30-micron-long par-
ticles include the following shapes (Plate 21):
1. Stubby, channeled fragments. These were
probably thin-walled, elongate vesicles, which are
now broken into short sections.
2. Curved, platelike shards.
3. Needle-shaped, pointed shards.
4. Flat, equant to slightly elongate particles,
with 4- to 8-micron-diameter vesicles.
5. Triangular (in cross section) to Y-shaped par-
ticles, slightly curved along the long axis. These
are vesicle walls from the junction of three ad-
jacent vesicles.
6. 20fx-100fi long, elongate pumice fragments.
These are rare in this particular sample.
ASH OF CARBONATITE COMPOSITION
OLDOINYO LENGAI, TANZANIA.?1966 eruption.
Oldoinyo Lengai is the youngest of the volcanoes
in the Neogene volcanic province of northern Tan-
zania, 19 km south of Lake Natron. According to
Dawson and others (1968), "the volcano is a steep
6,500 foot cone, with two summit craters. The vol-
cano is a dominantly pyroclastic cone with inter-
bedded lavas in which the general trend is from
phonolite-nephelinite-melanephelinite. The ejecta
are unique, containing a substantial portion of
sodium carbonate." Violent ash eruptions occurred
in August 1966, varying from minor emissions of
ash to major Plinian- and Vulcanian-type eruptions.
A new ash cone built up and ash was widely dis-
tributed on the slopes of the volcano. The sample
is from the surface, at the southern rim of the
Southern Crater.
Petrography: The ash consists of sodium car-
bonate (trona) with crystals of nepheline, pyrox-
ene, wollastonite, apatite, melanite, and pyrite.
The ash was black originally and turned white.
Lapilli are cemented by crystals of trona (Dawson
and others, 1968).
Morphology: The ash consists of nearly all min-
eral fragments (Plates 22), including perfect euhe-
dral (Plates 22A, 22F) and broken anhedral
nepheline crystals. All the ash particles are coated
with clumps of blade-shaped trona crystals. The
trona is secondary, having precipitated onto grain
surfaces after saturation of the ash with rainwater.
Hydrovolcanic (Phreatomagmatic) Eruptions
ASH OF BASALTIC COMPOSITION
CAPELINHOS, AZORE ISLANDS.?The sample is
hyaloclastic ash from the 1965 eruption. The
basaltic ash was deposited by hydrovolcanic (phre-
atomagmatic) eruptions in a shallow marine en-
vironment (Servico Geologicos de Portugal, 1959,
1962). Deposition was by airfall and base-surge
flows. The exact location of the ash sample is not
known.
Petrography: The vitric ash consists of pri-
marily reddish-brown, transparent sideromelane
fragments, with a trace of feldspar phenocrysts and
feldspar microlites in some of the large fragments.
Olivene and pyroxene are present as separate crys-
tal components of the ash. (86.3:0:5:8.7)
Morphology: The vitric ash consists of mostly
equant, block-shaped particles (Plate 23). The
grain surfaces are mostly planar faces, meeting at
nearly right angles. These surfaces are generally
flat and smooth, or conchoidal. The flat fracture
surfaces are characteristic of hyaloclastic ashes.
10 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
Vesicularity is very low; the vesicles are spherical
and only rarely are stretched into elongate shapes.
The skin characteristic of sideroraelane droplets
from magmatic eruptions is absent on sideromelane
fragments of hyaloclastic origin.
SURTSEY, VESTMANN ISLANDS, ICELAND. Surtsey
is a tuff ring formed in the ocean off the Icelandic
coast. The early stages of eruption were charac-
terized by violent phreatomagmatic eruptions.
Steam was generated when the seawater rushed into
the vent, resulting in vertical and base-surge erup-
tion clouds. Steam generation occurred at great
depths and near the surface (Thorarinsson, 1967).
The sample was collected from the deck of a Coast
Guard vessel, 3 km from the vent, on 1 December
1963.
Petrography: The vitric ash consists of sidero-
melane fragments, with phenocrysts of olivine
(Fo80) and plagioclase (An60) and no microlites.
There is a trace of tachylite. (98.5:Tr: 1.2:0)
Morphology: The ash consists of blocky sidero-
melane fragments (Plate 24) similar to the ash
particles from Capelinhos. Most of the fragments
are blocky and nearly equant. As in the Capelin-
hos ash, the vesicles are all spherical. The smooth,
planar grain surfaces are broken by depressions
where the fractures cut through vesicles.
TAAL, PHILIPPINES.?This sample is hyaloclastic
ash from the hydrovolcanic (phreatomagmatic)
eruptions of Taal in 1965 and was taken from the
backset beds of a base-surge dune, 1 km west of
the crater. The base-surge clouds, an important
mode of deposition of ash in hydrovolcanic erup-
tions (Fisher and Waters, 1969, 1970), consist of
clouds of steam, ejecta, and water that move
radially away from the vent, across the ground
surface, at hurricane velocities. These are associated
with tuff rings and explosion pits.
Petrography: The moderately well-sorted vitric
ash consists of equant, blocky sideromelane frag-
ments, equant tachylite fragments (these may be
from underlying, older ash deposits), augite crys-
tals, and feldspar crystals (^An45). (68.5:22.5:9.0:0)
Morphology: The vitric ejecta (Plate 25) is
similar, but not identical, to the ashes from Surt-
sey and Capelinhos. The main ash component con-
sists of a mixture of blocky and irregularly shaped
sideromelane fragments. None are vesicular; the
chilling of magma rising in the conduit must have
taken place at a depth where vesiculation had not
yet begun. Exotic (?) subrounded tachylite frag-
ments with rough grain surfaces make up a minor
component of the ash (Plate 25D). The tachylite
fragments, atypical of hyaloclastic ejecta, may have
come from older pyroclastic units underlying the
vent area, mixed in during the phreatomagmatic
eruptions.
TABLE ROCK, OREGON.?The Table Rock tuff-
ring complex in the Fort Rock-Christmas Lake
Valley Basin consists of a series of eight overlapping
tuff rings and a tuff cone. The tuff rings were
formed in a lake that existed during Pleistocene
time. The ash was deposited by base-surge flows
and by airfall during hydrovolcanic (phreatomag-
matic) eruptions. The ash forms very well-bedded
tuff rings around the crater. The sample was col-
lected 1 km from the vent of ring 2 of the complex.
Petrography: The sample is composed of light-
brown sideromelane, with thin rims of orange-
brown palagonite. There are only a few phenocrysts
and sparse microlites in the glassy fragments.
(94.4:0:3.7:0.6)
Morphology: The least altered sideromelane
fragments in this ash have grain surfaces pitted
by weathering, but are morphologically and petro-
graphically very similar to the ash from Surtsey.
The ash particles (Plate 26) are blocky, with planar
or slightly curved grain surfaces. The vesicularity
is low.
This older (Pleistocene) ash has been altered,
at least in part, to palagonite, a mixture of clays,
iron oxides, and zeolites. The fragments completely
altered to palagonite have scalelike grain surfaces
with thin spalls of the alteration product (Plate
26A). The original grain shapes can be determined
if the alteration is not complete and some glass
remains in the core of the particle.
KILAUEA, HAWAII.?1924 phreatic eruption. The
sample is of ejecta from the phreatic eruption in
Kilauea, which occurred when rising magma came
into contact with ground water in highly permeable
aquifers. Ground water penetrated the vent at
Kilauea and, on contact with incandescent ma-
terials, an enormous phreatic eruption was caused.
The eruption lasted 17 days, resulting in the col-
lapse of over 2 X 108 m3 of rock into the empty
vent. The exact location of this sample is not
known.
Petrography: The lithic-crystal ash contains
weathered, equant basalt fragments, hyalocrystal-
NUMBER 12 11
line basalt, olivine-rich basalt, tachylite, olivine
crystals, orthopyroxene crystals, opaque minerals,
and blocky sideromelane fragments. (33.3:0:35.2:
32.3)
Morphology: This ash is similar to the Taal
hyaloclastic ash; that is, it consists of a mixture of
juvenile hyaloclastic ash and comminuted rock
fragments from rock units below the vent area
(Plate 27). The lithic fragments are the main
constituent of this ash and consist of equant to
elongate basalt fragments, with rough or hackly
grain surfaces. Most have been pitted by weather-
ing as well. The smaller sideromelane fraction is
similar to the ashes from Capelinhos and Surtsey.
The fragments are characterized by smooth, planar
grain surfaces and low vesicularity.
ASH OF RHYOLITIC COMPOSITION
PANUM CRATER, CALIFORNIA.?Panum Crater is
a dome surrounded by a low-rimmed crater in the
Mono Craters chain. It is possible that it is a
maar of rhyolitic composition that erupted into
Mono Lake. The sample was collected from the
flank of the tuff ring.
Petrography: This is a crystal tuff, consisting
of crystalline components and colorless pumice
and shard fragments. The vitric and crystal com-
ponents are nearly equal. Crystal components in-
clude sanidine, plagioclase, orthopyroxene, horn-
blende, and biotite. (49.9:0:50.1:0)
Morphology: Although this ash (Plate 28) was
apparently thrown out during a hydrovolcanic
(phreatomagmatic) eruption, it is quite similar to
ashes from magmatic eruptions of rhyolitic and
andesitic magmas. The main difference between
this and rhyolitic ash from magmatic eruptions is
the presence of a significant proportion of small,
equant, blocky to bladelike shards (Plates 28E,
28F).
The pumice fraction consists of thin, elongate
fragments, with flattened pipe vesicles parallel to
the long axes of the grains. Some of the pumice
fragments (Plate 28D) have smooth outer surfaces.
These may have been parts of pumiceous fragments
enclosed by an outer skin.
SUGARLOAF, SAN FRANCISCO MOUNTAINS, ARI-
ZONA.?The vitric ash of rhyolitic composition is
from a Pleistocene (?) tuff ring at the base of the
eastern slopes of the San Francisco Mountains near
Flagstaff, Arizona. The ejecta consists of extremely
well-bedded ash in beds less than 1 mm to several
centimeters thick. Cross-bedded dunes within the
deposit indicate that part of the ejecta may have
been deposited by base-surge flows during the erup-
tion (Sheridan and Updike, 1971). The crater of
the ring is filled with a large dome extruded during
or after deposition.
It is probable that the ash is hyaloclastic; the
magma chilled on contact with ground water. The
blocky shard shapes, typical of hyaloclastic ash,
the presence of base-surge dunes, and the plastic
nature of the ash deformed by blocks thrown out
during the eruption favor a phreatomagmatic type
of eruption. The sample was collected on the north-
east flank of the tuff ring.
Petrography: This sample of rhyolitic lithic-
crystal ash consists of mostly colorless shards and
pumice fragments containing 5 to 30 percent sub-
parallel phenocrysts of K-feldspar, quartz, and
plagioclase. The shards are generally equant or
pyramidal and are subangular to rounded. Pumice
fragments have straight to slightly curved vesicles,
with average diameters of 0.01 mm and lengths
of approximately 0.3 mm. The rounded lithic frag-
ments consist of hyalocrystalline to equigranular
rhyolite. The matrix material of the ash, with an
approximate mean grain size of 0.01 mm, consists
of mostly angular, pointed glass shards and lesser
amounts of K-feldspar, quartz, and plagioclase.
(47:0:34.5:18.5)
Morphology: The ash is similar to that from
Panum Crater. The bulk of it consists of small,
equant, blocky to pyramidal vitric fragments (Plate
29). The vitric fragments have both smooth and
conchoidal grain surfaces. Most exhibit low vesicu-
larity.
Pumice fragments, most of which are less than
400 microns across, contain poorly developed ellip-
soidal to lensoidal vesicles. Blocky, rhyolitic lithic
fragments are quite often rounded, possibly by
grinding within the vent and ash cloud.
Ash from Littoral Steam Eruptions
Ash similar to that of tuff rings is characteristic
of littoral cones, which are built by steam explo-
sions generated when lava flows into a body of
water (Moore and Ault, 1965; Fisher, 1968). At
Puu Hou, Hawaii (Fisher, 1968), the production of
12 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
hyaloclastic sediments resulted from the rapid con-
version of water into steam by a high-temperature
lava flow. Evidence suggests that the explosions
occurred when steam was trapped beneath lava
crusts. The resulting varied mixture consists of:
(1) crystalline basalt fragments and olivine pheno-
crysts, (2) sideromelane fragments with a few small
vesicles, and (3) irregular, equant fragments with
no vesicles.
Fisher has distinguished three basic particle types
within the ashes from the Puu Hou littoral cones.
Type a?Vesicles are elongate or are spherical. Those with
stretched vesicles have fluidal edges. Those with spherical
vesicles are from presolidified pahoehoe crusts.
Type b?Frozen droplets?some are tear-shaped, or bizarre,
bent shapes. No pele's hair or spheres.
Type c?Irregular to equant with few or no vesicles from
broken portions of quickly chilled degassed lava.
Most of the basalt liquid was comminuted by the force
of steam explosions and cooled in air; less was cooled by
immersion in water. Pumice fragments with stretched vesicles,
many of which are irregular droplets indicates that vesicula-
tion occurred prior to cooling, but was not the cause of
comminution. Vesiculation halted and bubbles frozen before
fracturing in most of the pumice fragments, as shown by the
general absence of corners rounded by surface tension
(Fisher, 1968).
BASALTIC COMPOSITION
Puu Hou LITTORAL CONES, HAWAII.?The littoral
cones were formed by steam explosions when the
1868 lava flow reached the sea. Water entering the
interior of the flow caused the steam explosions.
The cones were built on both sides of the lava
flow, at the shoreline. The sample is from one of
the littoral cones.
Petrography: The vitric ash consists of (1) scal-
loped sideromelane fragments with abundant
vesicles; (2) drawn sideromelane glass with small
vesicles, elongate shapes, and fluidal edges (frozen
droplets); and (3) irregular or equant sideromel-
ane fragments with few or no vesicles (Fisher,
1968). (95.1:0:4.9:0)
Morphology: This ash is the most easily char-
acterized of all the ash samples in this study. The
ash consists of a mixture of blocky and pyramidal
sideromelane fragments (hyaloclastic), broken and
unbroken sideromelane droplets, and rough-
surfaced fragments of tachylite and sideromelane
flow crust (Plate 30).
The well-developed vesicularity near the flow
top accounts for the oddly shaped hyaloclastic com-
ponent of this ash. When the lava was chilled and
the resulting quench shattered by thermal stresses,
irregular pyramidal and crescent-shaped fragments
were formed. In contrast, hyaloclastics produced in
phreatomagmatic eruptions generally are blocky
and have low vesicularities or are nonvesicular.
The steam explosion resulting from the contact
of lava and water also carries out droplets of un-
quenched lava and bits of old flow crust in addition
to the hyaloclastic ejecta.
SAND HILLS LITTORAL CONE, HAWAII (historic).?
The Sand Hills cone is a recent (1848) littoral cone
formed when a flow from the northeast rift, Ki-
lauea, reached the sea. The sample is from the
cone.
Petrography: The ash consists of mostly sid-
eromelane fragments and droplets, containing
olivine phenocrysts and 5 to 20 percent feldspar
and opaque microlites. The droplets have a thin,
dark-brown skin that is not found on the hyalo-
clastic fragments. (97.7:0:2.3:0)
Morphology: The morphology of the ash frag-
ments (Plate 31) is identical to that of the Puu
Hou ash.
Ash-Size Particles of Meteorite Impact and
High-Energy Explosive Origin
RIES BASIN, GERMANY.?The Ries Basin, Ger-
many, is an impact crater, with ejecta consisting
of molten crystalline basement rocks and Mesozoic
sediments (Preuss and Schmidt-Kahler, 1969). The
fragments studied here were picked out of the
matrix of a suevite breccia. The photomicrographs
(Plate 32) are from papers by Horz (1965) and
von Engelhardt and Stdffler (1968).
Petrography: According to von Engelhardt and
Stoffler, "All fladen contain many vesicles; they are
mixtures of molten glasses and fine mineral frag-
ments. Phases contained in the fladen include dia-
plectic quartz glass, molten quartz glass, unaltered
feldspar, diaplectic feldspars, normal feldspar glass,
and diaplectic feldspar glass." Fladen consist of
multiple thin layers of glass that are alternately
poor and rich in angular mineral grains. Glass
within the fladen is heterogeneous and consists of
fine schlieren that differ in refractive index and
NUMBER 12 13
in color. "The structure reflects the heterogeneous
nature of the parent rock, the intense movement of
the melt, and the short duration of the molten
state" (von Engelhardt and Stoffler, 1968).
DIAL-PACK EXPLOSION, ALBERTA, CANADA.?An ex-
plosion of 4.5 X 105 kg of TNT at the ground
surface simulated a meteorite impact. The blast
produced a crater 72 m in diameter and 4.5 m deep.
Ejecta were thrown out in small rays. Small glass
spheres that formed in the fireball rained down
within and for at least 3.2 km from the crater in
the prevailing wind direction. The underlying rock
at the blast site consisted of lake sediments. The
inhomogeneous glass spheres formed by quick
melting in the fireball, followed by rapid quench-
ing (Heiken and Lofgren, 1971). This sample was
collected in the crater area immediately after the
explosion.
Petrography: The ejecta consist of blocks of
sediment underlying the blast center, fused soil,
and spherules. Only the fine-grained fragments
were studied here. These consisted of light-gray
to light-brown, inhomogeneous glass, exhibiting
light and slightly darker bands. Some of the bands
have slightly different refractive indices than the
bulk of the glass. There are a few anhedral, partly
melted feldspar crystals. A dark-brown skin, 10 to
20 microns thick, encloses the spheres. The spheres
are hollow; some contain only one large central
vesicle and others have several.
Morphology: Most of the fine-grained ejecta in-
volved in the fireball consist of glassy spheres (Plate
33). Most of the lunar spheres are studded with
smaller spheres imbedded or splashed onto the
surface. The debris-laden outer skin is rarely
broken by outer vesicles. The population of spheres
imbedded in or splashed onto larger spheres is
generally high, and smooth spheres are rare.
Conclusions and Summary
The ashes are best placed into two broad genetic
categories: magma tic and hydrovolcanic (phreato-
magmatic). Ashes from magmatic eruptions are
formed when expanding gases in the magma form
a froth that loses its coherence as it approaches
the ground surface. During hydrovolcanic erup-
tions, the magma is chilled on contact with ground
or surface waters, resulting in violent steam erup-
tions. Within these two genetic categories, ashes
from different magma types can be characterized
(Table 1).
In low-viscosity magmas, droplet shape is, in
part, controlled by surface tension, by acceleration
of the droplets as they leave the vent, and by air
friction. The ash particles consist of mostly sid-
eromelane or tachylite; the sideromelane particles
exhibit smooth, fluidal surfaces and a thin skin.
In magmas of higher viscosity, the morphology
of ash particles is controlled primarily by vesicle
density and shape, the vitric fraction generally con-
sisting of very angular pumice fragments and thin
vesicle walls, broken from pumice fragments during
or after the eruption. The morphology of the lithic
fragments is dependent on the texture and fracture
pattern of the rock type broken up during the
eruption.
The morphology of ash particles from hydro-
volcanic eruptions is controlled by thermal stresses
within the chilled magma, which result in frag-
mentation of the glass to form small blocky or
pyramidal glass particles. Vesicle density and shape
play a minor role in determining the morphology
of these ash particles. Table 1 is a summary of
the ash morphology of the ash samples collected.
It is hoped that this study will enable a worker
to infer the genesis and possibly the source of iso-
lated volcanic ash samples from stratigraphic sec-
tions or deep-sea cores.
Literature Cited
Cook, E. F.
1965. Stratigraphy of Tertiary Volcanic Rocks in Eastern
Nevada. Nevada Bureau of Mines Report, 11: 66
pages.
Dawson, J. B., P. Bowden, and G. C. Clark
1968. Activity of the Carbonatite Volcano Oldoinyo
Lengai, 1966. Geologische Rundschau, 57:865-879.
von Engelhardt, W., and D. Stoffler
1968. Stages of Shock Metamorphism in the Crystalline
Rocks of the Ries Basin, Germany. Pages 159-168
in Bevan M. French and Nicholas M. Short, editors,
Shock Metamorphism of Natural Materials. Balti-
more: Mono Book Corporation.
Fisher, R. V.
1961. Proposed Classification of Volcaniclastic Sediments
and Rocks. Geological Society of America Bulletin,
72:1409-1414.
14 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
1966. Rocks Composed of Volcanic Fragments and Their
Classification. Earth Science Reviews, 1:287-298.
1968. Puu Hou Littoral Cones, Hawaii. Geologische
Rundschau, 57:837-864.
Fisher, R. V., and A. C. Waters
1969. Bed Forms in Base Surge Deposits: Lunar Implica-
tions. Science, 165:1349-1352.
1970. Base Surge Bed Forms in Maar Volcanoes. American
Journal of Science, 268:147-180.
Fryxell, Roald
1963. Mazama and Glacier Peak Volcanic Ash Layers:
Relative Ages. Science, 147:1288-1290.
Heiken, Grant H.
1971. Tuff Rings: Examples from the Fort Rock-Christmas
Lake Valley, South-Central Oregon. Journal of
Geophysical Research, 76:5615-5626.
1972. Morphology and Petrography of Volcanic Ashes.
Geological Society of America Bulletin, 83:1961-
1988.
Heiken. Grant H., and Gary Lofgren
1971. Terrestrial Glass Spheres. Geological Society of
America Bulletin, 82:1045-1050.
Horz, Friedrich
1965. Untersuchungen an Riesglasern. Beitrage zur Min-
eralogie und Petrographie, 11:621-661.
Judd, J. W.
1888. On the Volcanic Phenomenon of the Eruption, and
on the Nature and Distribution of the Ejected
Materials. Pages 1-56 in G. J. Symens, editor, The
Eruption of Krakatoa and Subsequent Phenomena.
London: Trubner and Company.
Loney, Robert A.
1968. Flow Structure and Composition of the Southern
Coulee, Mono Craters, California?A Pumiceous
Rhyolite Flow. Geological Society of America
Memoir, 116:415-440.
McBirney, Alexander R.
1968. Compositional Variations of the Climactic Eruption
of Mount Mazama. Oregon Department of Geologi-
cal and Mineral Industries Bulletin, 62:53-57.
Moore, J. G., and W. V. Ault
1965. Historic Littoral Cones in Hawaii. Pacific Science,
19:3-11.
Moore, J. G., and W. G. Melson
1969. Nu?es Ardentes of the 1968 Eruption of Mayon Vol-
cano, Philippines. Bulletin Volcanologique, 33:600-
620.
Nakamura, Kazuaki
1964. Volcano-Stratigraphic Study of Oshima Volcano:
Izu. Bulletin of the Earthquake Research Institute
of Japan, 42:649-728.
Norrish, K., and J. T. Hutton
1969. An Accurate X-Ray Spectrographic Method for the
Analysis of a Wide Range of Geological Samples.
Geochimica et Cosmochimica Ada, 33:431-453.
Rittman, Alfred
1962. Volcanoes and Their Activity. 305 pages. New York:
John Wiley and Sons.
Servico Geologicos de Portugal
1959. Le Volcanisme de L'Isle de Faial et l'eruption de
Volcan de Capelinhos. Memoir (Nova Serie), 4: 100
pages.
1962. Le Volcanisme de L'Isle de Faial et l'eruption de
Volcan de Capelinhos. Memoir (Nova Serie), 9: 54
pages.
Sheridan, M. F., and R. G. Updike
1971. Sugarloaf Tephra-A Rhyolitic Deposit of Base
Surge Origin in Northern Arizona [abstract]. Geo-
logical Society of America Proceedings, 3:191-192.
Stoiber, Richard E., and William E. Rose
1970. The Geochemistry of Central American Volcanic
Gas Condensates. Geological Society of America
Bulletin, 81:2891-2912.
Tanguy, J. C.
1971. Mount Etna Volcanic Eruption. Smithsonian Center
for Short-Lived Phenomena Bulletin, December 15,
1971.
Thorarinsson, Sigurdur
1967. Surtsey-The New Island in the North Atlantic. 47
pages. New York: Viking Press.
Van Padang, M. Hermann
1951. Indonesia. Part I in Catalogue of the Active Vol-
canoes of the World. 271 pages. Naples: Inter-
national Volcanological Association.
Verhoogan, J.
1951. Mechanisms of Ash Formation. American Journal
of Science, 249:729-739.
Walker, G. P. L., and R. Croasdale
1972. Characteristics of Some Basaltic Pyroclastics. Bulle-
tin Volcanologique, 35:303-317.
Wentworth, C. K.
1938. Ash Formation of the Island of Hawaii. Special Re-
port of the Hawaiian Volcano Observatory, 3: 183
pages.
Wilcox, Ray E.
1965. Volcanic Ash Chronology. Pages 807-816 in H. E.
Wright and D. G. Frey, editors, The Quaternary of
the United States. Princeton, N.J.: Princeton Uni-
versity Press.
Williams, Howel
1942. The Geology of Crater Lake National Park, Oregon.
Carnegie Institution Publications, 540: 162 pages.
Appendices
APPENDIX 1: CHEMISTRY OF THE VOLCANIC ASHES
STUDIED FOR THIS REPORT
Unless otherwise specified, the X-ray fluorescence
analyses were made by Mike Rhodes, Kay Parker,
and John Evans, Lockheed Electronics Company,
NASA-Manned Spacecraft Center.
Most of the major elements (Si, Ti, Al, Fe, Mn, Ca, K, P,
and S) were determined by X-ray fluorescence analysis, using
a glass disk prepared by fusing 280 mg of powdered sample
with a lanthanum-bearing lithium borate fusion mixture.
Preliminary concentrations obtained for these samples were
used to calculate matrix corrections, which in turn were
applied to the preliminary data to obtain final corrected con-
centrations. This technique has been described and evaluated
fully by Norrish and Hutton (1969).
The other elements were measured on separate aliquots of
the sample; sodium by atomic absorption spectroscopy and
ferrous iron and water by conventional chemical techniques.
(Rhodes, 1971, personal communication.)
1. Pacaya: Rhodes, analyst.
2. Fuego: Baird, analyst, in Stoiber and Rose (1970).
3. Cerro Negro: Rhodes, analyst.
4. Etna: sample is of lava flow from the South Vent, May 7,
1971. Lenable, analyst, in Tanguy, J. C, (1971).
5. Kilauea Iki, 1959: Rhodes, analyst.
6. Kilauea Crater-Reticulite: Rhodes, analyst.
7. Ash from Aloi-Alae Craters area-Hawaii: Rhodes, analyst.
8. Taal, Philippines: Rhodes, analyst.
9. Ruapehu, New Zealand: Rhodes, analyst.
10. Merapi, Indonesia: Rhodes, analyst.
11. Mayon, Philippines: Rhodes, analyst.
12. Krakatau, Indonesia: collected on Perbuwatan. R. G.
Reiber, analyst; in Van Padang (1951).
13. Santiaguito, Guatemala: Rhodes, analyst.
14. Katmai, Alaska: Rhodes, analyst.
15. Analysis of white pumice, 15 feet above the creek bed at
the Pinnacles, Crater Lake, Oregon. Ken-ichiro Aoki,
analyst, in McBirney (1968).
16. Ash from Oldoinyo Lengai, Tanzania: from Dawson et al.
(1968).
17. Capelinhos, Azores: Guimares and Viera, analysts (Servico
Geologicos de Portugal, 1959).
18. Surtsey, Iceland: from Thorarinsson (1967).
19. Table Rock, Oregon: Heiken, analyst.
20. Panum Crater, California: analysis is of rhyolite from
the Southern Coulee, Mono Craters (Loney, 1968) .
21. Puu Hou, Hawaii: Rhodes, analyst.
22. Sand Hills, Hawaii: Rhodes, analyst.
23. Ries Basin, Germany: from von Engelhardt and Stoffler
(1968). An average of nine unrecrystallized glass bombs
collected at nine different localities around the Ries
Basin.
APPENDIX 2: GAS RELEASE STUDY OF SELECTED
VOLCANIC ASHES
Everett K. Gibson, Jr.
Selected volcanic ash samples have been analyzed
for their gas contents and weight loss during heat-
ing under vacuum. The analytical technique em-
ployed was a combined thermal analysis-mass
spectrometric procedure described previously (Gib-
son and Johnson, 1971, 1972; Gibson, 1972; Gibson
and Moore, 1972). A Mettler recording vacuum
thermoanalyzer interfaced to a Finnigan 1015 quad-
rupole mass spectrometer was used for the analysis.
The mass spectrometer source was placed directly
in the reaction chamber. With this arrangement
the evolved gaseous species could be analyzed rap-
idly and without requiring gas transfer procedures.
Sample sizes ranged from 20 mg for volatile rich
ashes to 200 mg for ash samples which were de-
pleted in volatiles. Samples were heated at 6?C/
minute from room temperature to temperatures up
to 1400?C under a vacuum of 10/6 torr. The sam-
ple's weight loss along with released gaseous species,
abundances, temperature ranges, and sequences of
release were determined simultaneously on the
sample during the heating cycle. The sensitivity
of the analytical balance used for weight-loss studies
was ? 0.05 mg. Sample temperatures were meas-
ured with calibrated platinum/platinum-10 per-
cent rhodium thermocouples located at the base of
the platinum sample crucibles. Spectra were ob-
tained every 5?C during the heating cycle. Re-
producible background spectra were obtained
during the bakeout procedures before sample
analysis began and were later subtracted from the
obtained spectra.
Everett K. Gibson, Jr., Geochemistry Branch, TN7, NASA,
Johnson Space Center, Houston, Texas 77058.
15
16 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
The ash samples were neither crushed nor
homogenized before analyses, under the assump-
tion that gas-filled vesicles or inclusions might be
ruptured. The petrographic descriptions of the ash
samples analyzed have been given previously by
Heiken (1972 and this atlas), with the exception
of the basaltic ashes from Hekla. The Hekla ashes
were collected during the summer of 1970 by Carle-
ton B. Moore of Arizona State University, Tempe,
Arizona.
A summary of the weight-loss data on the ash
samples analyzed is given in Table 3. The weight-
loss data has been calculated from the thermo-
grams obtained from the thermal analysis-gas
release measurements.
The gas release profiles for the ash samples
analyzed are given in Figures 1 to 16. The system
background has been subtracted from each spectra
taken at a given temperature. The gases which
are in low concentrations have been multiplied
by factors of 10 and 100, to allow plotting on the
same release profile. For example: if H2O is plotted
as X 1 and CO2 is plotted as X 10, the H2O con-
centration is 10 times that of the CO2 or stated
another way, the CO2 concentration is one-tenth
that of the water concentration. In selected samples
containing large quantities of volatiles, the num-
bers given at the top of the release peaks represent
how much higher the peak goes before it decreases.
The same scaling factor is used as that given below
100 percent relative abundance.
Literature Cited
Gibson, Jr., E. K.
1973. Thermal Analysis-Mass Spectrometer-Computer Sys-
tem and Its Application to the Evolved Gas Analy-
sis of Green River Shale and Lunar Soil Samples.
Thermochimica Ada, 5:243-255.
Gibson, Jr., E. K., and S. M. Johnson
1971. Thermal Analysis-Inorganic Gas Release Studies of
Lunar Samples. Proceedings of the Second Lunar
Science Conference, 2:1351-1366. Cambridge: Massa-
chusetts Institute of Technology Press.
1972. Thermogravimetric-Quadrupole Mass-Spectrometric
Analysis of Geochemical Samples. Thermochimica
Ada, 4:49-56.
Gibson, Jr., E. K., and G. W. Moore
1972. Inorganic Gas Release and Thermal Analysis Study
of Apollo 14 and 15 Soils. Proceedings of the Third
Lunar Science Conference, 2:2029-2040. Cambridge:
Massachusetts Institute of Technology Press.
Heiken, Grant H.
1972. Morphology and Petrography of Volcanic Ashes.
Geological Society of America Bulletin, 83:1961?
1988.
NUMBER 12 17
TABLE 1.?Volcanic ash summary
A. Magmatic eruptions*
Magma type Basaltic Rhyolitic and dacitic Carbonatite (one sample)
Volcanic fea- Cinder cones, lava lakes, basalt flows, and
tures associ- ash interbeds in strato-volcanoes,
ated with the
ash
Petrography Mostly droplets and broken droplets of
sideromelane (clear, brown basaltic glass)
and tachylite (black, submicrocrystalline
basalt); phenocryst population is variable.
Chemistry of SiO2, 48 to 52 percent
samples Total Fe as Fe203, 10 to 13 percent
studied A12O3, 12 to 19 percent
Morphology 1. Irregular droplets with fluidal shapes
(spheres, ovoids, dumbbell and teardrop
shapes).
2. Broken droplets; some with original
droplet surface present.
3. Long, thin strands of glass (Pele's
hair).
4. Polygonal, lattice-like network of
glass rods; highly vesiculated froth.
The grain shapes vary from a dominance of
spheres and droplets in lavas of very low
viscosity to irregular elongate, often
broken droplets from lavas of slightly
higher viscosities; some droplets have
been twisted around a central axis; all
are highly vesicular.
Smooth, fluidal surfaces broken by smooth-
lipped vesicle cavities (these broke while
the surface was still fluid) and cavities
with angular rims (these near-surface
vesicle walls broke after the surface of
the grain was chilled).
In detail, the surface skin, formed soon
after ejection from the vent, is broken by
parallel joints through which some later
liquid may protrude (and Is chilled).
Some particles have warty surfaces.
Strato-volcanoes, domes, thick short
lava flows, and ash-flow tuff units.
The main components (vitric, crystal,
lithic) vary, but all are generally
present; the vitric component includes
colorless glass shards and pumice frag-
ments; generally containing oriented
microlites; lithic fragments include
andesite of varying textures and stages
of alteration and igneous and sedimen-
tary xenoliths; broken crystals of pla-
gioclase, pyroxene, and opaque minerals
are coninon.
SiO2, 56 to 59 percent
Total Fe as Fe203, 6 to 8 percent
A12O3, 16 to 19.5 percent
1. Vitric component: equant to elon-
gate pumice fragments; dependent on
the shape of the vesicles in the
fragment; elongate pumice fragments
contain elongate, ovoid to tubular
vesicles; fragments are irregular;
only the exposed vesicle walls are
smooth.
Flat, pointed shards with smooth or
conchoidal fracture surfaces are
probably broken vesicle walls.
2. Lithic fragments: These are general-
ly equant; the surface is entirely
dependent on the texture and fracture
of the rock type; some of the frag-
ments are rounded.
3. Crystal fragments: Shape is governed
by the fracture of the mineral; most
appear to have been broken during the
eruption.
Domes and flows, some strato-volcanoes,
calderas, and hypothetical fissure
vents which are sources for ash flows;
ash-flow tuff sheets.
Generally, there is a great amount of
colorless glass with variable amounts of
microlites and phenocrysts; phenocrysts of
quartz, sanidine, biotite, and small
amounts of other ferro magnesian minerals;
small amount of lithic (rhyolitic or xeno-
lithic) fragments.
SiO2, 63 to 74 percent
Total Fe as Fe203, 1.9 to 5.3 percent
A12O3, 13 to 17 percent
1. Vitric fragments: elongate to equant
pumice fragments (grain shape is de-
pendent on vesicle shape) with thin
vesicle walls; curved, Y-shaped, or flat
thin shards are vesicle walls; these are
very smooth and rarely chipped except by
later reworking of the ash.
2. Lithic fragments are generally equant in
these ash samples.
The surfaces of pumice fragments are very
rough, broken vesicles; no smooth surfaces
other than vesicle walls; there are no
smooth fluidal surfaces similar to those
of droplets in low-viscosity lavas.
Strato-volcanoes, ash cones.
Ash and lapilli consisting of
crystals of sodium carbonate,
nepheline, pyroxene, wollastonite,
apatite, melanite, and pyrite are
cemented by blade-like sodium
carbonate crystals.
SiO2, 25.23 percent
Fe as Fe203, 8.71 percent
A12O3, 5.72 percent
Perfect crystals of nepheline and
broken (irregular but equant)
crystals of the other components
listed under petrography.
Surfaces of nearly all the grains
are coated with bundles of thin,
bladed sodium carbonate crystals;
the bundles are 5 to 50 microns
thick; the bundles of sodium car-
bonate are generally concentrated
in depressions in the grain sur-
faces.
B. Hydrovolcanic[Phreatomaqmatic] eruptiorst C. Ash-size vitric particles ofmeteorite impact origin
Manna type Rhyolitic Basaltic (littoral)5
Volcanic fea-
tures associ-
ated with the
ash
Petrography
Chemistry of
Samples
Studied
Morphology
Maar-type volcanoes: tuff
cones, and explosion pits.
ings, tuff
Vitric ash.
Angular fragments of sideromelane; general-
ly free of all crystals except phenocrysts;
the lithic component of some ashes is de-
pendent on the stratigraphy of rocks under-
lying the maars and the amount of magma
reaching the surface.
SiO?, 45 to 47 percent
T-i-1 Fe as Fe."
16 to 17
Total Fe as Fe2?3' 10 to 13 percent
17 percent
Equant blocky glass fragments with low
vesicularity.
Smooth flat fracture surfaces are formed
when the glasses contract and fracture
after chilling; these fracture faces cut
across vesicles if the particles are
vesicular.
Tuff ring with a central dome.
Most ash particles consist of equant
or elongate colorless glass fragments;
traces of rhyolitic lithic fragments;
the glass is generally free of micro-
lites or contains very few microlites.
SiO2, 75.4 percent
Fe as Fe203, 0.9 percent
Al203, 13.5 percent
Sharply pointed elongate shards and
flat elongate pumice fragments.
faces of each arlin the ves'cTeLtul Ulth vesicle
wans are smgoin.
Littoral cones.
Vitric to vitric-lithic ash: the sample
consists of mostly sideromelane droplets,
tachylite, and fragments of aphanitic
basalt.
SiO2, 50 to 51 percent
Total Fe as Fe203, 11.5 percent
A12O3, 12 to 13 percent
1. Crystalline basalt fragments; equant
lithic fragments.
2- Sideromelane glass fragments with fewvesicles; these may be blocky or cres-
cent shaped. the shape my be con_
trolled mainly by vesicle shapes.
3. Nonvesicular pyramidal glass fragments
Impact craters: wide shallow
craters with low ejecta rims.
Nonvesicular to highly vesicular;
generally very inhomogeneous glass
with abundant schlieren of dif-
ferent refractive indices and
mineral detritus; shocked minerals
are present in the detritus.
Dependent on the target surface
and partly on composition of the
meteorite.
Glass droplets (complete and bro-
ken) a few microns to several
centimeters in diameter; abundant
smaller spheres, droplets, and
rQck fragments are welded t0 tne
surface of larger spheres.
Th , , nenerallv smooth?^1 ?* E S
The droplets and broken droplets have round
fluidal surfaces with sharp angular lips
around depressions caused by the breaking
of the vesicle wall of a vesicle located near
The exposed vesicle walls have smooth curved
surfaces.
Fracture surfaces of hyaloclastic grains have
t The eruptions are caused primarily by the steam gene- ? The ash is formed when lava flows into the sea and
rated when rising magma comes into contact with shal- water penetrates into cracks in the flow surface,
low bodies of surface water, ice, or ground water;
magmatic gases add to the energy of i;he eruptions.
' The eruptions are caused by rapid release of gases or
frothing in the magma as it reaches the surface, re-
sulting in (1) large-scale ash eruption (Plinian, Vul-
canian, or Pelean) with resulting ash falls and ash
flows; high-viscosity lavas; associated lahars or vol-
canic mudflows if the eruption is into a crater lake
or is accompanied by rainstorms; and (2) lava fountain-
ing and ash eruptions (Hawaiian and strombolian types)
of low-viscosity lavas.
18 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
TABLE 2.?Chemistry of the ashes studied
Chemistry
SiO2
TiO2
Al,Ot
Fe2O,
FeO
MnO
MgO
CaO
Na2O
K2O
P2O8
s
H2O+
H2O-
Cl
Total
Total Fe as
Fe2Os
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
51.8
1.15
17.73
2.96
6.49
0.22
4.03
9.52
4.05
0.83
0.26
0.06
49.42
0.87
19.09
6.75
10.07
3.09
0.60
0.41
49.2
1.28
19.38
4.42
5.55
0.14
5.41
11.89
1.76
0.85
0.05
47.38
1.68
17.44
6.00
5.16
5.52
10.77
3.42
1.71
0.50
0.06
99.10 100.83 99.93 99.79
10.35 10.61 9.97 11.16
48.17
2.44
11.65
1.87
9.66
0.22
10.84
1055
3.08
0.49
0.25
0.11
99.03
12.61
49.29 48.57
2.51 2.12
14.12 10.78
1.48
-? 10.19
0.23 0.23
7.33 14.04
10.44 9.41
2.75
0.35 0.38
0.23 0.22
0.09 0.08
52.71
0.86
16.10
10.99
_#
0.25
5.52
9.99
3.37
0.03
0.18
0.06
97.38 100.25 100.06
12.79 12.81 10.99
58.58
0.63
15.68
2.49
3.15
0.10
3.18
5.58
3.17
1.52
0.12
2.17
96.39
5.99
55.99
0.69
19.4
7.04
_?
0.22
1.91
7.69
453
2.40
059
0.06
99.92
7.04
56.32
0.68
19.13
7.81
_#
0.20
3.71
8.54
4.15
1.16
0.28
0.12
102.1
7.81
65.14
0.48
15.28
2.57
1.79
0.14
1.38
3.17
3.77
2.89
0.06
0.42
2.24
0.74
0.13
100.2
4.36
(13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23)
SiOa
TiO2
A12O,
Fe2O3
FeO
MnO
MgO
CaO
Na2O
K2O
PaO6
s
H2O+
H2O-
Cl
Total
Total Fe as
Fe2O,
62.44
0.48
16.69
2.98
2.08
0.21
2.48
5.02
4.56
1.54
0.20
0.07
98.75
5.29
73.52
0.22
12.15
0.49
158
0.07
0.52
1.29
4.10
2.90
0.04
0.02
96.60
1.91
71.82
0.49
15.07
1.33
0.89
0.06
0.44
1.91
5.02
2.89
0.07
99.99
2553
0.46
5.72
8.71
_?
0.38
1.62
14.10
18.65
4.89
1.49
0.31
1.15
4.89
1.13
100.33
252 8.71
COS?8.75
BaO_1.00
SO, ?153
F -J0.62
47.59
2.65
17.05
2.97
7.44
050
5.47
9.09
4.57
1.85
0.50
0.07
0.37
99.82
10.41
46.5
2.28
16.8
1.65
10.8
0.20
7.62
9.45
3.32
0.33
0.03
0.02
99.00
12.45
44.45
1.27
9.73
9.97
_?
0.17
7.98
10.51
3.34
1.36
4.2
6.0
98.98
9.97
75.4
0.04
13.5
0.42
0.50
0.05
0.10
0.42
3.8
4.8
0.71
0.17
100.00
51.53
2.02
13.15
11.34
_#
051
8.13
9.87
3.17
0.42
0.24
0.08
100.16
11.34
50.46
2.29
12.22
11.58
_?
051
11.75
9.98
2.84
0.41
0.24
0.11
63.54
0.81
15.10
0.99
3.75
0.10
2.71
3.45
2.86
3.71
0.36
2.73
102.09 100.48
11.58 4.74
CO2?0.37
Insufficient material for FeO determination.
NUMBER 19
Sample
Santiaguko Dacitic ? -
Oldoinyo Lengai
Hekla-Tephra
Mayon Volcano-
Philippines 1968
andesitic airfall .. ,.
Cerro Negro-Nicaraugua
Basaltic ash ......
Taal-Philippines-1968
Ruapehu-no
SH|)]Jni3tCS
Ruapehu-with
sublimates
Surtsey 1963
Mt. Spurr, Alaska
1963, andesitic ash
Sugar Loaf, Arizona
Pacaya, Guatemala
Basaltic
Katmai, Alaska-] 912
Hekla
Merapi, Indonesia ...
Panum Crater, Cali-
fornia Pleistocene . .
Sample
wt.
(mg)
127.66
21.42
161.45
42.32
51.85
62.30
150.82
153.03
47.62
46.0
197.67
156.22
22.43
85.17
38.12
40.31
100?C
0.063
3.78
0.0
0.047
0.019
0.0
0.34
0.22
0.021
0.48
0.025
0.006
0.18
0.012
0.11
0.20
200?C
0.094
3.97
0.012
0.095
0.058
0.016
0.56
1.29
0.042
0.98
0.28
0.019
1.20
0.035
0.24
0.55
TABLE
300?C
0.12
4.30
0.031
0.14
0.077
0.032
0.66
1.63
0.063
1.83
0.68
0.064
1.74
0.059
0.34
1.067
3.?Weight
400?C
0.14
5.00
0.056
0.19
0.096
0.048
0.83
2.12
0.13
3.37
1.11
0.083
2.14
0.11
0.50
1.41
500cC
0.16
8.50
0.074
0.21
0.14
0.064
1.19
3.27
0.29
5.57
1.37
0.10
2.32
0.12
0.66
1.64
losses for volcanic ash
600 ?C
0.17
14.15
0.11
0.26
0.15
0.080
1.29
3.59
0.40
7.22
1.51
0.13
2.41
0.14
0.68
1.71
Percent
700?C
0.20
18.58
0.17
0.31
0.17
0.096
1.52
4.05
0.57
7.76
1.59
0.16
2.50
0.16
0.71
1.79
weight
800?C
0.21
20.26
0.22
0.33
0.21
0.11
1.62
4.41
0.67
8.30
1.64
0.19
2.59
0.20
0.74
1.86
loss
900?C
0.24
21.62
0.27
0.38
0.25
0.14
1.72
4.80
0.71
8.67
1.68
0.22
2.67
0.22
0.79
1.89
1000?C
0.27
24.42
0.33
0.45
0.33
0.18
1.79
5.16
0.84
8.83
1.76
0.29
2.81
0.27
0.84
1.98
1100?C
0.31
32.31
1050?C
0.55
1080?C
0.57
0.41
0.32
1.89
5.42
1.15
9.022
1.86
0.42
2.90
0.45
0.97
2.009
1200?C
0.38
0.66
0.48
0.51
1.96
5.69
1.43
9.20'
U50?C
1.92
0.58
2.99
0.79
1.10
2.059
1300X
0.48
0.97
0.75
1.17
2.12
2.110
1.99
135O?C
0.98
3.076
1.36
1.50
2.11
1250?C
1400?C 1450?C
0.60 1.33
1.61
1.31
2.42
3.12
4.018
1.90
3.17
20 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100
Sample wt 156.22 mg
a>
a
0)
a
co
TJC
3J3
O
-40-(xl00)
-34-(xl00)
-64-(xl00)
-44-(xl00)
20 -
200 400 600 800
Temperature, ?C
1000 1200 1400
FIGURE 1 Pacaya, Guatemala: Basaltic. The Pacaya basaltic ash is depleted in volatiles. The
sample lost only 0.29 percent by weight after heating to 1000?C. The ash sample did not contain
any absorbed gases. Water was released slowly over the complete heating range, with the
maximum release occurring near 500?-600?C. Carbon dioxide was released in three regions.
Below 350?C, a small amount of CO2 was released. Between 400? and 550?C, CO2 is suddenly
released from the decomposition of carbonate phases such as calcite or a similar carbonate. At
temperatures above 700?C, carbor> dioxide is slowly evolved. This CO2 results from residual
carbon reacting with the silicate matrix to evolve CO2. Upon heating to 1400? C, the Pacaya
basaltic ash lost only 1.90 weight percent. The low abundance of volatiles in the Pacaya ash is
characteristic of its high temperature history.
NUMBER 12 21
100 Sample wt 51.85 mg
co
c
3
O
H2 - 2- (x 100)
H2O - 18- (x 10)
CO2 "44- (x 100)
CO, N2 ~ 28- (x 10)
Ar - 40- (x 100)
H2S - 32- (x 100)
200 400 600 800 1000 1200 1400
Temperature, ?C
FIGURE 2.?Cerro Negro: Basaltic. The basaltic ash from Cerro Negro is extremely depleted
in its volatile gases and low temperature mineral phases. The gas release pattern shows only
trace amounts of H2O released over the complete temperature range. Trace amounts of CO2
are released above 1000?C, and the CO, is undoubtedly a reaction product produced at the
elevated temperatures. The Cerro Negro ash sample lost only 1.31 weight percent (total) during
the heating to 1400?C. The Cerro Negro basaltic ash is typical of basaltic ashes which are
depleted in their inorganic gases and are characteristic of their past high temperature histories.
22 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100 Sample wt 161.45 mg
80
20
133 m
I
height
o 60
a
u1
C
3
Qa
a, 40
>
Kelat
COS
H2S
" so2
HF
H2O - 18
CO2 - 44 - (x 10)
CO, N2 - 28 - (x 100)
- 60 - (x 100)
- 34 - (x 100)
- 64 - (x 100)
- 20 - (x 100)
CO 2^ !
H2O W
200
I I I I I
400 600 800
Temperature, ?C
FIGURE 3 Hekla: Basaltic. The Hekla tephra is, extremely depleted in volatiles. The sample
does not contain any terrestrially absorbed gases such as H2O, CO2 and/or CO, N2 which are
normally released below 150?C. The sample lost less than 0.01 percent total weight during
heating below 200?C. The released CO2 shows evidence of a possible carbonate decomposition
between 300? and 400?C. The carbonate'is probably secondary because of the high temperature
history of this tephra sample. Trace amounts of the unusual gases HF and COS are seen in the
gas release profile of the ash sample. The gases released above 700?C are reaction products of
components found within the basaltic ash. Upon heating under vacuum to 1050?C, the sample
lost only 0.55 percent total weight loss, further evidence of the high temperature history of the
sample.
NUMBER 12
100
Sample wt 85.17 mg
169 m
80
H2 -2 -(xlOO)
H2O - 18 - (x 10)
CO2 - 44 - (x 100)
CO, N2 - 28 - (x 10)
H S - 34 - (x 100)
SO2 - 64 - (x 100)
a>a
co
"0c
3
60
/CO2
40
20 H2O
200 400
I i i r
600 800
Temperature, ?C
24 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100 Sample wt 150.82 mg
80
ca
C3
_QO
ex.
60
40
20
161 m
H2 - 2 - (x 100)
H2O- 18 - (x 100)
H2S - 34 - (x 100)
CO2 - 44 - (x 10)
SO2 - 64 - (x 10)
CS2 - 76 - (x 100)
200 400
I I I
600 800
Temperature, ?C
1000 1200 1400
FIGURE 4 Ruapehu airfall: Andesitic (no sublimates). The Ruapehu airfall ashes contain
moderate amounts of volatiles. The sample contains adsorbed water which is released around
100?C. Water is the most abundant gas released from the Ruapehu ash. Carbon dioxide is the
second most abundant gas phase released, and is released in two regions. Between 350? and
500 ?C, a small amount of CO, is evolved, which is probably from a secondary carbonate.
Additional CO2 is released above 1000?C and is a reaction product. Sulfur dioxide is released
in two distinct temperature regions. SO/ is released between 300?-500?C and 600?-700?C.
The SO2 evolved is from the decomposition products of secondary sulfate minerals. H2S is
released gradually over the complete temperature range and is probably a reaction product. At
temperatures above 1100?C, CS2 is released, which results from the reaction of carbon and
sulfur-bearing phases. The Ruapehu airfall ash lost 3.12 weight percent upon heating to 1400?C.
100
Sample wt 153.03 mg
80
?S
co
"DC
3JQ
O
60
40
20
H2
H2O -
- 2
18
- (x 100)
- (x 1)
CO2 - 44 - (x 10)
CO - 28 - (x 10)
- 40 - (x 100)
- 34 - (x 100)
- 64 - (x 100)
148 m
200 400 600 800
Temperature, ?C
FIGURE 5 Ruapehu airfall: Altered airfall. The altered Ruapehu ash contains the second
largest quantity of volatile phases that we have observed during gas release studies of volcanic
ashes. The volatiles observed undoubtedly arise from the secondary sublimates which are found
on the surfaces of the ash particles (Heiken, 1972). During heating of the sample to 1200?C,
the total weight loss was 5.69 percent. Most of the weight loss (4.80 percent) occurred below
900?C. Large quantities of water were released in two distinct temperature intervals. Adsorbed
water and structural water from mineral phases, which are not thermally stable at temperatures
above 300?C, were first released, followed by release of structurally bound water (between 350?
and 550?C) associated with the sulfates (gypsum, etc.). During the second water release, sulfur
dioxide was released in large quantities from the sulfate mineral phases. Sulfur dioxide and
hydrogen sulfide were also released below 250 ?C. These gaseous species were either dissolved
in the adsorbed water or strongly adsorbed to the ash particles. Carbon-bearing gases, CO2 and
CO, were released between 300? and 500 ?C and probably result from decomposition of carbonate
phases such as calcite, siderite, and magnesite. Carbon dioxide and carbon monoxide were
released in small quantities between 600? and 800?C and could arise from dolomite decomposi-
tion. At temperatures above 900? C, only small quantities of volatile phases are released. The
large quantity of volatiles released from the Ruapehu ash are derived from secondary alteration
of the ash samples by either ground water or vapor-bearing gas or fluid phases, which have
since modified the ash samples.
1400
26 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCE
100 Sample weight 38.02 mg
mm' 173m
CM CO ?
I I
co2l I
80
H2 - 2 - (xlOO)
H2O - 18 - (xl)
CO2 - 44 - (xlO)
H2S - 34 - (xlOO)
SO2 - 64 - (xlOO)
C?2 ,'CO2
I!
co
c
3
_Q
D
QC
60
200 400 600 800
Temperature, ?C
1400
FIGURE 6 Merapi, Indonesia: Andesitic. The Merapi andesitic ash has undergone secondary
alteration as evidenced by the low temperature release of water and carbon dioxide. Below
400 CC, loss of water accounts for almost all of the weight loss (0.50 weight percent). The
water released results from both adsorbed water and decomposition of hydrate phases. Carbon
dioxide is suddenly evolved between 400? and 525 ?C. The CO2 release is from decomposition
of carbonate phases, primary calcite. At temperatures above 1000? C, carbon dioxide is evolved
a second time. The high temperature CO2 release is from a reaction product of residual carbon
phase, with the silicate melt. During heating under vacuum to 1300?C, the Merapi ash lost a
total of 1.50 weight percent.
NUMBER 27
100
Sample wt 42.32 mg
H2
H2O
- 2 - (x 100)
-18 -(x 10)
80 CO2 - 44 - (x 100) ?CO - 28 -(x 100)
H2S - 34 - (x 100)
SO2 - 64 - (x 100)
co
-oc
3
D
60
138 m
\co2
200 400 600 800
I I
1000 1200 1400
Terrmerature. ?C
FIGURE 7?Mayon, Philippines: Andesitic airfall. Mayon ash is a volatile depleted andesitic
ash. The airfall sample analyzed shows evidence of terrestrially adsorbed H2O which is released
below 150?C. Carbon dioxide release near 400?C is characteristic of trace amounts of carbonates
such as calcite. The CO2 evolved between 600? and 700? C is similar to the release pattern of
dolomites (??) or higher temperature carbonates. The andesite ash contains only trace amounts
of sulfur-bearing phases which release SO2 at temperatures above 700?C. The large COB release
profile between 1000? and 1300?C results from reaction products of carbon-bearing phases and
the silicate melt. The Mayon volatile depleted airfall andesitic ash is characteristic of similar
ashes which have had a high temperature history and retained very few volatiles. The weight
loss for the Mayon ash was 1.61 percent (total) after heating to 1400?C.
28 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100
Sample wt 46.0 mg
o>
'35
-C
co
c
3
_Q
D
a>
?oooooool
? ? ? es ^- <* CJ! H2 -2 - (x 100)
H2O - 18 - (x 1)
CO2 - 44 - (x 10)
- 28 - (x 10)
- 60 - (x 100)
- 40 - (x 100)
- 34 - (x 100)
- 64 - (x 100)
Mt Spurr, Alaska
200 400
i r
600 800
Temperature, ?C
1000 1200 1400
FIGURE 8.?Mt. Spurr, Alaska: Andesitic. The Mt. Spurr andesitic ash contains an unusually large
quantity of volatile species which are released during heating to 1100?C. The major gas phase
released is CO2, which is associated with the decomposition of carbonate phases such as calcite,
Na2CO8, magnesite, siderite. Trace amounts of H2, H2O, COS, HjS, and Ar are also released.
The sample lost 7.76 percent by weight below 700 ?C and 9.20 weight percent after heating to
1150?C. The low temperature (< 500? C) appearance of COS during the heating of the Mt. Spurr
ash is very unusual. This phase normally is evolved at temperatures above 600 ?C in the presence
of carbon and sulfur-bearing phases under reducing conditions.
NUMBER 12 29
Sample wt 127.66 mg
co
-oc
3
-Q
a
0)
OS
10
200
FIGURE 9.?Santiaguito, Guatemala: Dacitic. The gas release curve indicates the depletion of
volatiles from the airfall-collected ash. The water released below 150?C accounts for 0.085
percent of the total weight loss of the sample. The water is mostly adsorbed as indicated by
the low temperature release (< 150?C). Trace amounts (< 5 ppm) of CO8 and N2 are also
released below 150?C. The CO2 is apparently dissolved within the adsorbed HeO. Between 200?
and 500 ?C, a small release of CO2 occurs and is apparently from trace amounts of secondary
carbonates. At 850?C a sudden release of CO2 is noted. The CO2 is believed to result from
rupturing of tiny gas-filled vesicles or tightly bound CO2 trapped within microcavities of the
ashes. The increase in CO2 release above 1100CC results from reaction products of residual
carbon phases with the silicate melt. The depletion of gases from the Santiaguito dacite ash is
typical of airfall-collected dacite ashes. The sample lost 1.33 weight percent during heating under
vacuum to 1450"C.
1400
30 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100
Sample wr 22.43 mg
H2 - 2 - (x 100)
H2O - 18 - (x 1)
H2S - 34 - (x 100)
CO2 - 44 - (x 10)
80
60
40
I I I
200 400
I I I r
600 800
Temperature, ?C
1000
FIGURE 10 Katmai, 1912: Rhyolitic. The Katmai ash has undergone secondary alteration. The
sample contains large amounts of water-bearing phases. The ash sample lost 1.74 weight percent
below 300?C, with CO2 contributing to only a few percent of the weight loss below 300?C.
Water is the major volatile phase released (below 800 ?C). Minor amounts of CO2 and HJJS
are also evolved from the sample. Above 800? C, carbon dioxide is the major gas phase evolved.
The CO2 evolution is from a reaction product of residual carbon with the silicate melt. After
heating to 1450?C, the sample lost only 3.17 weight percent. The largest region of weight loss
is below 400?C and occurs with the loss of secondary alteration product volatiles.
NUMBER 12 31
100 Sample wt 21.42 mg
o>
200 400
i r r
600 800
Temperature, ?C
1000 1200
FIGURE 11.?Oldoinyo Lengai: Carbonatite. The Oldoinyo Lengai ash is one of the most volatile-
rich ashes examined. The majority of the gases released are H2O, COa, and SO2, with minor
amounts of HF, Ar, H2S, O2, CO, and N2. The gas release pattern shows below 100?C the
loosely adsorbed gases H2O (major species), CO2, CO/N2, and HF. Between 300? and 700?C,
decomposition of the carbonate phases Na2CO3, CaCO3, etc., occurs. The carbon dioxide release
in this temperature range accounts for almost 60 percent of the total volatiles released from the
Oldoinyo Lengai ash. Decomposition of sulfur-bearing phases (e.g., CaSO4, MgSO*, etc.) or
chemical reaction products of the sulfur-bearing phases with the silicates is evidenced by the
release of SO... and H2S between 700? and 1050?C, which accounts for almost 40 percent of the
total weight loss for the ash sample. The volatile-rich ash sample lost 32.3 percent total weight
during heating to 1050? C under vacuum.
1400
32 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100
Sample wt 47.62 mg
80
O>
'55
co
?DC
3_Q
a
60
40
20
137 m
H2
H2O
co2
CO, N2
COS
H2S
SOo
- 2 -
- 18 -
- 44 -
- 28 -
- 60 -
- 34 -
- 64 -
(x
(x
(x
(x
(x
(x
(x
100)
1)
100)
10)
100)
100)
100)
200 400
I I I I
600 800
Temperature, ?C
I I I
1000 1200 1400
FIGURE 12 Surtsey 1963 ash: Basaltic hyaloclastic. The Surtsey ash is depleted in its volatiles.
The sample does not have any adsorbed gases which are typically released at temperatures
below 200?C. Trace amounts of CO2, HjS, and COS are released between 300? and 600?C.
Water is gradually evolved from the sample between 400? and 800? C. The gradual water
release appears to result from a diffusional controlled type of release and not from the decom-
position of hydrates. Hydrogen is released between 600? and 800?C. At temperatures above
1000?C, CO2, CO, N2, H2, and SO2 are evolved. These high temperature species are typical of
reaction products of carbon, sulfur, oxygen, and hydrogen gases at the elevated temperature.
During the heating of the Surtsey ash to 1000?C, only 0.84 weight percent was lost and only
4.01 weight percent after heating to 1400?C.
NUMBER 12
100 Sample wt 62.30 mg
80 -
0)
co
c
3.a
o
CO, N2 - 28 - (x 10)
- 44 - (x 100)
20 -
200 400 600 800
Temperature, ?C
1000 1200 1400
FIGURE 13 Taal: Basaltic hyaloclastic. The basaltic ashes from the Taal 1968 eruption are
depleted in volatiles. The ash sample did not evolve significant gases until above 1000?C. A
sudden release of CO2 at 700?C is characteristic of vesicular rupture. The CO2 evolved above
1000?C is a reaction product of carbon-bearing phases with the silicate containing matrix.
The sample has not been altered by secondary oxidation. Heating to 1200?C, the sample lost
0.51 weight percent and after 1400?C, 2.42 weight percent was lost from the ash sample. The
depletion of volatile gases and absence of low temperature mineral phases from this basaltic
ash is a direct result of the high temperatures associated with the phreatomagmatic eruption
of the Taal volcano.
34 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
100
Sample wt 40.31 mg
174 m
80
JC
'3
co
TJ
C
3
JQ
O
60
40
20 -
- (x 100)
- (x 10)
- (x 100)
. (x 10)
- (x 100)
CO2|
.??*
H2O
H2
CO, N2
200 400 600 800
I I
1200 1400
Temperature, ?C
FIGURE 14?Panum Crater, California: Rhyolitic hyaloclastic. The Panum crater rhyolitic ash
has undergone extensive secondary alteration. The Pleistocene ash sample shows evidence of
extensive weathering by ground water. Below 600 CC, the sample lost large quantities of water,
approximately 85 percent of the total gases released. Only trace quantities of H2, CO2, CO, and
H2S were released. Above 1000 ?C, the released CO2 is noted. The CO2 results from residual
carbon reacting with the silicate mineral phases at elevated temperatures. The Panum Crater
ash lost a total of 2.11 percent by weight during heating to 1250?C, with 1.71 percent of this
weight loss occurring below 600?C.
NUMBER 12
100
80
co
-0c
3
.0
a
_0
a:
60
40
20 -
KKN'.K
H2OJ
fI
\ A
v \
Sample wt 197.67 mg
195 m
H2 - 2 - (x 100)
H2O - 18 - (xlO)
CO2 - 44 - (xlOO)
H2S -34 - (x 100)
SO2 -64 - (x 100)
200 400 600 800 1000 1200 1400
Temperature, ?C
FIGURE 15 Sugarloaf, Arizona: Rhyolitic hyaloclastic. The Sugarloaf hyaloclastic ash contains
only water which is released below 600?-700?C. Only trace quantities of CO2, US, H2, and SO2
are released from the ash. The water released below 700 ?C accounts for 1.59 weight percent of
total 1.99 percent weight loss which the ash sample underwent. The water which was evolved
from the ash is undoubtedly derived from the secondary alteration of the sample before
collection.
PLATES 1-33
NUMBER 12 37
Clast size
>256
64-256 mm
2-64 mm
1/16-2 mm
<1/16 mm
Clast name
Coarse blocks
Fine blocks
Lapilli
Coarse ash
Dust (or
fine ash)
Rock name
(if majority of clasts
in the size range)
Pyroclastic breccia
Lapilli stone
Tuff
B
25
10/
/
Crystal
Lithic
50
25
Crystal-lithic Vitric-lithic
Crystal
50
PLATE 1
25 10 Vitric
Classification of volcaniclastic fragments, A, Size classification (Fisher, 1961).
B, Compositional classification (Cook, 1965).
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 2
Pacaya, Guatemala, A, SEM of basaltic vitric ash, consisting of light-brown sideromelane droplets
and broken droplets. (Sideromelane refers to light- to medium-brown transparent glass [in thin
section] of basaltic composition. Under a binocular microscope, sideromelane particles may
appear to be black or very dark brown.) The grains in the center and upper left have fluidal
shapes with smooth botryoidal surfaces. Round lumps on the grain surfaces were formed when
expanding vesicles deformed the flexible outer skin. The 10- to 50-micron-thick flexible brown
skin visible on many sideromelane droplets appears to have formed immediately on exposure to
the atmosphere. In many droplets, this skin is broken by vertical joints a few microns apart and
10 to 50 microns high. In some cases, fluid from the droplet interior has forced its way through
the cracks (Heiken and Lofgren, 1971) . The dark-brown color of the skin is partly due to the
closely spaced cracks and partly due to oxidation of the grain surface. Some vesicles broke open
while the skin was still viscous, resulting in a smooth, curved lip around the cavity edge. The
droplet in the center has a rough-ribbed appearance caused by the expansion of elongate pipe
vesicles. The thin thread on the upper part of the grain is due to complete collapse of a vesicle
while the droplet was still molten. (The scale is 100 microns.) B, Photomicrograph of
sideromelane droplet twisted around its long axis during flight. The smooth fluidal surface
has a thin, dark-brown skin that was formed immediately after extrusion. The large phenocrysts
visible are of calcic plagioclase. (The scale is 100 microns.) c, SEM. All are broken droplets
except the slightly rounded lithic fragment (aphanitic basalt) on the left. The fragment on
the right has elongate, slightly flattened pipe vesicles, which were possibly shaped by flow
before comminution. (The scale is 50 microns.) D, Photomicrograph of a broken sideromelane
droplet. The outer skin is dark brown and can be seen on the round surfaces. Both broken
ends are angular and lack the skin. The grain in the upper right corner is an olivine phenocryst.
(The scale is 100 microns.) E, SEM of broken sideromelane droplets. The equant grain shape
seems to be related to equant or slightly deformed vesicles. There is a crystal fragment (feldspar)
in the foreground. (The scale is 100 microns.) F, Photomicrograph of the outer edge of a
sideromelane grain; cross section of an elongate vesicle similar to those causing the ribbing
of the grain in A. (The scale is 100 microns.)
NUMBER 12 39
40 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 3
Fuego, Guatemala, A, SEM of a broken sideromelane droplet. The smooth triangular patch is
part of the droplet skin. The original smooth droplet surface is easy to distinguish from the
irregular or conchoidal fracture surfaces of the broken sections. (The scale is 25 microns.)
B, SEM of a broken vitric fragment with slightly deformed vesicles that are 20 to 125 microns
in diameter. (The scale is 25 microns.) c, Photomicrograph of broken sideromelane and tachylite
droplets characteristic of this ash. Nearly all the grains in this photo are a mixture of
sideromelane and tachylite. (The scale is 100 microns.) D, SEM of a broken sideromelane
droplet with very low vesicularity. The fracture along the long axis of the grain appears to
correspond with a line of small vesicles. (The scale is 25 mircons.) E, SEM. The fragment
in the foreground is a lithic fragment, probably aphanitic basalt. The fragment in the back
is a broken droplet characterized by a smooth fluidal grain surface. (The scale is 50 microns.)
NUMBER 12 41
42 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 4
Cerro Negro, Nicaragua. (All scales are 100 microns.) A, SEM of dark-brown sideromelane
droplets. The smooth botryoidal outer surface or skin was deformed by expansion of the
outermost vesicles. Vesicles open to the exterior were formed by (1) the bursting of gas
bubbles (smooth cavity edge, rounded by surface tension), or (2) the breaking of the outer
vesicle wall after the grain surface was rigid (sharp angular cavity edges). B, Photomicrograph
of a sideromelane droplet (center) and tachylite fragments. There are abundant olivine and
feldspar phenocrysts in the glass, c, SEM of an angular broken sideromelane droplet, D, Photo-
micrograph of an angular tachylite fragment (submicrocrystalline basalt). These fragments
rarely have rounded fluidal edges.
NUMBER 12
44 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 5
Etna, Italy, A, SEM of a 116 X 52 micron agglutinate grain; glass-covered feldspar (?) laths
are oriented parallel to the long grain axis. The grain is composed of several glassy grains
welded together. (Scale is 13 microns.) B, SEM of a slightly elongate tachylite grain with an
irregular, hackly surface. The hemispherical depression at the bottom of the grain is a broken
vesicle. (Scale is 26 microns.) c, Closeup of B. Parts of the grain surface exhibit a diktytaxitic
texture, consisting of an open framework of glass-coated feldspar crystals. The void space in
these irregular areas is about 30 percent. (Scale is 3.3 microns.) D, SEM of a triangular, broken
glass droplet. Vesicles exposed at the surface are 110 to 200 microns in diameter. Vesicle walls
are coated with small droplets, which may be sulfur. Fracture surfaces are conchoidal. (Scale
is 22 microns.) E, Photomicrograph of clear brown glass (sideromelane), tachylite grains,
and a clinopyroxene grain. The sideromelane grains have low vesicularities and blocky shapes;
this is unusual and normally characteristic of hyaloclastic ashes. These are broken droplets,
however, as indicated by some grain edges which exhibit a "skin" characteristic of magmatic
basaltic ash. The tachylite grains exhibit scalloped edges, which are across broken vesicles.
(Scale is 61 mircons.) F, Photomicrograph of a partially oxidized brown glass droplet and
several angular tachylite grains. (Scale is 61 microns.)
NUMBER 12 45
46 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 6
Deception Island, Antarctica, A, Photomicrograph of very poorly sorted vitric ash, consisting
of broken sideromelane droplets and ragged equant tachylite fragments. There are only a few
olivine phenocrysts in addition to feldspar microlites visible in the sideromelane. (The scale
is 100 microns.) B, SEM of a fine-grained basaltic ash. Most of the ash fragments have low
vesicularity and are very angular. Rough fragment surfaces indicate chipping and grinding of
ash particles during the eruption or by later reworking. (The latter idea is improbable.)
(The scale is 100 microns.) c, SEM of a diktytaxitic glassy fragment. Feldspar microlites or
very small phenocrysts with thin glass coatings form an open network where either (1) some
of the fluid drained out from between the crystals, or (2) the vesicle shape was controlled by
crystal shape and orientation. (The scale is 100 microns.) D, SEM; closeup of c. (The scale
is 10 microns.) E, Photomicrograph of a broken sideromelane droplet exhibiting subparallel
feldspar microlites oriented by flow. (The scale is 100 microns.) F, SEM of an elongate broken
sideromelane droplet. Smooth round surfaces are of the outer skin. (The scale is 10 microns.)
NUMBER 12
47
PLATE 7
Kilauea Iki, Hawaii, A, SEM of a scoriaceous sideromelane fragment, probably a broken droplet. Vesicle diameters range from
2 to 500 microns. Smaller vesicles adjacent to larger ones broke through the bubble walls instead of indenting them. (The
scale is 100 microns.) B, SEM of a highly vesicular sideromelane droplet. Most of the vesicles are connected, forming an open
network of spherical or ovoid chambers. The outer surface has a well-developed skin. (The scale is 100 microns.) c, SEM of
the tail of a droplet formed during flight. If the elongation were completed, a Pele's hair would have been formed. (The
scale is 100 microns.) D, Photomicrograph of a sideromelane droplet. The round edges on the top and right edges have a
thin, dark-brown skin. The light-brown transparent glass is homogeneous. (The scale is 1 mm.) E, SEM of a sideromelane
droplet with a flange around it that was possibly due to spinning. Holes in the surface are due to the breaking of outer vesicle
walls after the hardening of the outer skin. (The scale is 100 microns.) F, Edge of a sideromelane droplet. The skin, with
parallel contraction cracks, has been deformed by air drag. Dark circular areas are bubbles in the mounting medium. (The scale
is 100 microns.) c, SEM of a 1.96-mm-diameter Pele's hair. The hair is ribbed, with ribs 20 to 300 microns across. The
larger (300 micron) ribs are about 4.5 mm long and tapered at both ends. The ribs are slightly sinuous, possibly due to
twisting about the long axis of the hair. (Scale is 280 microns.) H, Photomicrograph of a Pele's hair, with a bulge over an
olivine phenocryst. The elongate vesicles are about 4 microns in diameter. (Scale is 61 microns.) i, SEM of a 253-micron-
diameter Pele's hair, with a ribbed surface. Each rib is over an elongate vesicle. Adhering to the surface are 1- to 2-mircon-
thick, curved Pele's hairs. (Scale is 40 microns.) j, Photomicrograph of a 46-micron-diameter Pele's hair. The hair surface
is smooth, broken only by small lumps over microphenocrysts of olivine and feldspar. The glass is pale brown (sideromelane) .
(Scale is 15.5 microns.) K, Detail of c. This is small-scale ribbing, consisting of square-edged ridges, 1 to 3 microns wide,
separated by flat or slightly convex depressions, 2 to 5 microns wide. These may be cracks in the skin of the grain, where a
vesicle erupted to the grain surface while the grain was still molten (left side of the photograph) ; the ribbing was spread
and compressed around the vesicle. (Scale is 9 microns.) L, Photomicrograph of a 290-micron-diameter, vesicular Pele's hair.
There appears to be a correlation between the degree of vesicularity and the number of ribs on a Pele's hair. The more vesic-
ular grains have abundant ribs parallel to the long axis. (Scale is 61 microns.)
50 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 8
Glass spheres from Kilauea Iki. A, SEM of a smooth brown sideromelane sphere. Holes in the
surface are over outer vesicles. (The scale is 100 microns.) B, Photomicrograph of the edge of
a sideromelane sphere similar to the one in A. Dark circles are vesicles filled with grinding
compound. Phenocrysts are olivine and feldspar. (The scale is 500 microns.) c, Photomicrograph
of the skin on a sphere edge, showing cooling joints deformed by air drag. (The scale is 100
microns.) D, SEM; closeup of a sideromelane sphere, showing smooth-walled depressions (col-
lapse of outer vesicles before solidification) and depressions with ragged edges (outer skin
broken after solidification) . (The scale is 10 microns.) E, SEM of a dumbbell-shaped
sideromelane droplet. The shape may be due to spinning that forced fluid to the extremities
of the droplet. (The scale is 100 microns.)
NUMBER 12 51
fe:'^^>*&^i
0
52 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 9
Reticulite ash, Kilauea, Hawaii, A, SEM of lattice-like framework of triangular sideromelane
rods, formed during extreme frothing of lava during lava fountaining. The triangular cross
section is the line of contact between three expanding gas bubbles. (The scale is 100 microns.)
B, Photomicrograph of a fragment similar to the one in A. There are no phenocrysts or microlites
in the sideromelane. (The scale is 1 mm.) c, SEM. Surfaces of the reticulite lattice have been
altered by weathering, and are cracked. (The scale is 100 microns.) D, Photomicrograph of
reticulite. Details of triangular rods in cross section, showing smooth vesicle walls at the mutual
contact between three bubbles. (The scale is 100 microns.)
NUMBER 12 53
54 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 10
Aloi-Alae vent, Hawaii (1969-1970 eruption). A, SEM of the edge of a broken, vesicular,
sideromelane droplet. Compare the outer skin (right) with a slight texture or roughness to
the smooth curved fractures across the grain (left) . Note the 2- to 8-micron-thick skin exposed
around the lip of a surface depression at the center bottom. (The scale is 100 microns.) B, SEM
of a twisted, brolten sideromelane rod that may have formed in the same manner as Pele's
hair. (The scale is 100 microns.) c, SEM of part of a sideromelane sphere with a smooth
surface. (The scale is 100 microns.) D, Photomicrograph of the interior of a clear sideromelane
sphere, exhibiting spherulites of pyroxene (?) crystals. Spherulites are rare in glasses of basaltic
composition. (The scale is 50 microns.)
NUMBER 12 55
56 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 11
Oshima, Japan, A, SEM of a broken sideromelane droplet partly immersed in the mounting
medium. (The scale is 10 microns.) B, Photomicrograph of vitric-crystal ash, consisting of
mainly sideromelane (medium-gray grain in center) and tachylite (black scoria) droplets.
(The scale is 1 mm.) c, SEM. Blocky glass fragment on the right is probably part of a broken
sideromelane droplet. The grain has low vesicularity, with only a few vesicles, 1 to 5 microns
in diameter. Both particles are partly covered with sublimates. (The scale is 10 microns.)
D, Photomicrograph of equant sideromelane and tachylite droplets. (The scale is 1 mm.)
E, SEM of a scoriaceous sideromelane fragment that has been altered, probably by weathering.
(The scale is 10 microns.) F, Photomicrograph of a vesicular sideromelane droplet welded to
an angular tachylite fragment. Agglutinates similar to this one are common in this ash
sample. (The scale is 100 microns.)
NUMBER 12 57
58 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 12
Taal (ash from the cinder cone), 1958. A, Photomicrograph of a twisted sideromelane droplet
(center), with a well-developed dark-brown skin. The tapered droplet tail was broken off.
The glass contains 10 to 15 percent randomly oriented microlites of feldspar and pyroxene.
The black grains are broken tachylite fragments. On the right and at the bottom of the
photograph are sideromelane grains of hyaloclastic origin. (The scale is 100 microns.) B, SEM
of a sideromelane droplet. The droplet appears to have twisted around the long axis during
ejection from the vent. Surface bulges overlie vesicles or phenocrysts immediately below the
droplet surface. (The scale is 10 microns.) c, SEM of a plagioclase crystal, with a thin glass
coating welded to the surface. Horizontal parallel lines are albite twin planes. (The scale
is 50 microns.) D, SEM of a broken sideromelane droplet. (The scale is 50 microns.)
E, Photomicrograph of a broken sideromelane droplet. A dark-brown skin is well developed
on the unbroken surfaces. Black grains are tachylite fragments. Other sideromelane fragments
are blocky, do not have an outer skin, and are probably of hyaloclastic origin. (The scale is
100 microns.) F, SEM of a sideromelane droplet that has a smooth fluidal surface. White
fragments are smaller glass fragments and crystals lying on the grain surface. (The scale is
100 microns.) G, SEM of a tachylite grain that lacks the smooth grain surfaces characteristic
of unweathered sideromelane. (The scale is 50 microns.) H, SEM of a tachylite fragment with
somewhat irregular rough-walled vesicles. (The scale is 100 microns.) I, SEM of a broken
sideromelane fragment, similar to those in D and F. (The scale is 50 microns.)
NUMBER 12 59
60 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 13
Makaopuhi?Pele's hair, A, SEM of a smooth, cylindrical Pele's hair. The hair is broken at
a bulge, exposing an ovoid, thin-walled vesicle (1-3 microns thick). The hair surface is perfectly
smooth, with a few 1- to 2-micron-thick hairs stuck to the surface. (Scale is 100 microns.)
B, SEM of same hair as in A. Several millimeters from the broken hair end, there is a change
from a cylindrical to ribbed shape. In the lower part of the photo, the skin is broken over an
elongate vesicle, resulting in a thin, dagger-shaped depression. (Scale is 210 microns.) c, SEM
of a ribbed, 250-micron-diameter Pele's hair. There is one 165-micron-wide rib, flanked by
11- to 25-micron-wide ribs. The irregular lump is over a phenocryst beneath the grain surface.
The grain surface is smooth, with the exception of patchy sublimate coatings. (Scale is 35
microns.) D, Photomicrograph of Pele's hair. These "hairs" are characterized by relatively low
vesicularity. Vesicle walls and grain surfaces are deformed over clots of olivine and feldspar
phenocrysts. The pale brown glass is homogeneous. (Scale is 154 microns.) E, Photomicrograph
of a thin, nonvesicular hair, tapered to a point at one end. The hair is deformed over a clot
of olivine phenocrysts; 18 percent of the hairs in this sample are nonvesicular. (Scale is '61
microns.) F, Photomicrograph of a vesicular Pele's' hair. The extremely long, very thin vesicles
in this hair are characteristic of Pele's hair from lava fountains. The bulge in the hair is over
an olivine phenocryst. (Scale is 25 microns.) G, Photomicrograph of a Pele's hair, near a
large bulge. The ovoid or spherical vesicles near the bulge are very unusual in a Pele's hair.
Normally they are stretched out parallel to the long axis of the hair. The glass is pale brown
and homogeneous; there are no patches of devitrifiied glass in this sample. (Scale is 154 microns.)
NUMBER 12 61
62 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 14
Pahoehoe Flow Crust (crushed). A, SEM of a T-shaped brown glass fragment, consisting of a
mutual wall between 3 large vesicles (5 mm to 1 cm diameter). Vesicle walls are curved and
quite smooth except for some shallow depressions and lumps (over phenocrysts.) There are no
smaller vesicles in the vesicle wall. In cross section, the I-shaped vesicle walls are as thin as
100 microns. Broken grain surfaces have a hackly to conchoidal fracture. (Scale is 830 microns.)
B, Photomicrograph of the glass wall between three vesicles. It is pale brown, clear glass
(sideromelane), with about 5 percent phenocrysts (feldspar and olivine) and 5 to 10 percent
small patches of spherulites. (Scale is 154 microns.)
NUMBER 12 63
64 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 15
Ruapehu, New Zealand, A, SEM of a broken light-brown glass droplet. The grain surface is
partly covered with sublimates. (The scale is 10 microns.) B, Photomicrograph of a clear
colorless pumice fragment, rounded either during the eruption or by later reworking. The
outer edges were oxidized, resulting in a rim of a darker color glass. (The scale is 100 microns.)
c, SEM. The center fragment is possibly a feldspar phenocryst, completely covered with
sublimates. (The scale is 100 microns.) D, SEM of lithic-vitric ash. On the upper left is a
feldspar phenocryst. Other fragments are andesite or colorless glass. All fragments are covered
with a thin layer of sublimates. (The scale is 100 microns.) E, Photomicrograph of lithic-vitric
ash, consisting of fragments of aphanitic andesite; mudstone; medium-crystalline pyroxene-
hypersthene andesite; tachylite; feldspar-rich aphanitic andesite; crystals of andesine, hypersthene,
and augite; and fine-grained glass shards and pumice. (The scale is 500 microns.) F, SEM of
a vesicular equant glass fragment. Irregular fractures and pitting of grain surfaces indicate
that the ash may have been reworked by water or wind. (The scale is 100 microns.)
NUMBER 12 65
66 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 16
Merapi, Indonesia, A, SEM of colorless glass shards that are partly covered by small (< 2
microns), loosely adhering glass fragments. The center shard has a single irregularly shaped
vesicle. (The scale is 10 microns.) B, SEM. The large fragment in the center is a broken
plagioclase crystal, exhibiting good albite twinning. (The scale is 10 microns.) c, SEM of
mostly angular nonvesicular glass shards. The pointed fragments in the foreground are char-
acteristic of this ash sample. (The scale is 10 microns.) D, Photomicrograph of a grain mount
of this crystal-vitric ash, consisting of plagioclase, orthopyroxene, clinopyroxene, sharp angular
and colorless glass shards, and opaque minerals. The ash is very fine grained and very well
sorted. (The scale is 100 microns.)
NUMBER 12 67
gg SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 17
Mayon, Philippines, A, SEM of colorless to gray/brown-colored vitric-crystal ash, consisting of
mostly blocky or elongate shards and broken crystals, 5 to 20 microns long. (The scale is 100
microns.) B, Photomicrograph of vitric-crystal ash. In the center is a colorless vesicular glass
fragment containing feldspar microlites. The edges of the fragment were oxidized to a dark
reddish-brown color. The finer grained ash particles consist of broken crystals of augite,
hypersthene, and plagioclase; colorless glass; and small, equant andesite fragments. (The scale
is 100 microns.) c, SEM. At center right is a vesicular glass fragment. Most of the vesicles
exposed at the grain surface were spherical. (The scale is 10 microns.) D, SEM of a vitric
fragment containing ovoid or elongate vesicles up to 15 microns long. Angular fragments on
the surface or in the center vesicle are loosely adhering fine-ash fragments. (The scale is 10
microns.) E, Photomicrograph of a scoria fragment consisting of colorless glass with oxidized
zones around the edge and around some vesicles. (The scale is 100 microns.) F, SEM of an
angular glass shard that is typical of the vitric portion of this ash sample. The smooth, slightly
curved surface on the right is probably a vesicle wall remnant. (The scale is 10 microns.)
NUMBER 12 69
70 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 18
Ash from Krakatau. Sketches copied from Plate IV of Judd (1888). (Scale is 100 microns.)
A, Pumice dust (ash) which fell on board the Arabella, when about 1800 km from Krakatau.
There is only a trace of phenocrysts at this distance. The sample consists of elongate U- or
Y-shaped shards, which are broken vesicle wall fragments, B, Material similar to A, formed by
crushing "common" Krakatau pumice in a mortar.
NUMBER 12 71
B
72 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 19
Santiaguito, Guatemala, A, SEM of a plagioclase crystal exhibiting albite twinning. Loose
crystal fragments make up a substantial portion of this ash. (The scale is 50 microns.)
B, Photomicrograph of a hyalocrystalline dacite fragment (lithic) . Equant dacite fragments
make up most of this ash. (The scale is 100 microns.) c, SEM of a broken vitric fragment. (The
scale is 50 microns.) D, SEM of a broken vitric fragment partly coated with sublimates. The
vesicles have irregular twisted shapes. (The scale is 50 microns.) E, Photomicrograph of an
irregularly shaped hyalocrystalline fragment. The vesicle in the center has an odd irregular
shape that is characteristic of the vesicles in this ash of dacite composition. (The scale is 50
microns.) F, SEM of a lithic ash consisting of equant dacite fragments and vesicular vitric
fragments. (The scale is 100 microns.)
NUMBER 12 73
74 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 20
Katmai, Alaska, A, SEM of a colorless pumice fragment, with pipe vesicles 5 to 50 microns
in diameter. Vesicle walls are 0.5 to 2 microns thick. The overall grain shape is controlled by
vesicle shape. (The scale is 100 microns.) B, SEM; closeup of A, showing in detail the vesicle
shapes and thin vesicle walls. (The scale is 100 microns.) c, Photomicrograph of a pumice
fragment similar to those in A and B. The vesicles are parallel with pipe or pod shapes. The
glass is colorless. Dark spots are opaque minerals. (The scale is 100 microns.) D, SEM of
pumice and shards, consisting of transparent colorless glass. All particles in the field of view
are vitric fragments. (The scale is 100 microns.) E, SEM; closeup of the pumice fragment in
D, illustrating different stages in the development of elongate pipelike vesicles. In the center is
a nearly spherical vesicle. The pipe-shaped vesicles were formed by elongation and compression
of spherical vesicles by flow in the extremely viscous magma near the ground surface. Small
particles loosely adhering to the grain surface are small angular shards. (The scale is 100
microns.) F, Photomicrograph of a pumice fragment (center) and many shards that are tri-
angular or needle-like in cross section. Most of the shards are broken vesicle walls. (The scale
is 100 microns.) G, SEM of chains of spherical and podlike vesicles in different stages of being
stretched out to form elongate pipe vesicles. Fragmental material in vesicles and on the surface
are small shards loosely adhering to the surface of the pumice grains. (The scale is 20 microns.)
H, SEM of a vitric fragment that is unique for this sample because the vesicles are not drawn
out into pipe shapes. Most of the vesicles are flattened ovoids. Part of this fragment has no
vesicles. (The scale is 10 microns.)
NUMBER 12 75
76 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 21
Mazama ash. A, SEM of glass fragments ranging from 2.4 to 12 microns long. There are mostly
elongate, furrowed, and curved platelike grains. Dust adhering to the grain surfaces is generally
less than 1 micron in diameter The channeled fragments are thin walls of parallel, elongate
vesicles, broken into short sections. (Scale is 7.3 microns.) B, SEM of a flattened, rectangular
fragment with flattened, ovoid vesicles (ranging from 5 to 14 X 30 microns) . Vesicle walls and
surfaces are very smooth. (Scale is 10 microns.) c, SEM of a 100-micron-long pumice fragment.
Pumice fragments of this size are rare in this sample. The vesicle walls are 1 to 3 microns
thick. (Scale is 10 microns.) D, Photomicrograph of a pumice fragment and several angular
shards. The glass is colorless, and contains very few microlites. Compare the cross section of
the pumice grain to the SEM photograph of a similar grain in c. (Scale is 15.5 microns.)
Photomicrograph of a group of shards which are typical of this sample. Angular, curved, or
Y-shapes are common. The grain on the right is a very small pumice fragment, with one intact
vesicle. (Scale is 6.5 microns.)
NUMBER 12 77
78 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 22
Oldoinyo Lengai, Tanzania, A, SEM of a carbonatite ash. Several excellent hexagonal nepheline
crystals are visible in this sample. Other crystals are completely coated with trona. (The scale
is 100 microns.) B, SEM; closeup of the surface of a nepheline crystal, showing clumps of trona
crystals. These may have formed by solution and precipitation on grain surfaces by rainwater.
(The scale is 10 microns.) c, SEM of ash fragment (nepheline crystal?) partly covered with
trona crystals. (The scale is 100 microns.) D, SEM; closeup of the surface of the grain in c.
Delicate intergrown bladelike crystals of trona fill most of the depressions in the grain surface.
(The scale is 10 microns.) E, Photomicrograph of carbonatite ash. The clear crystals are
nepheline coated with trona. The opaque clots are aggregates of trona and small crystals of
apatite, pyroxene, and wollastonite. There are some small dark-brown glass spheres in this
sample. (The scale is 1 mm.) F, Photomicrograph of a euhedral nepheline crystal in the ash.
It is zoned with crystals of apatite growing parallel to the outer rims of the grain. (The scale
is 100 microns.)
NUMBER 12 79
80 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 23
Capelinhos, Azore Islands. (All scales are 100 microns.) A, SEM of equant blocky sideromelane
fragments. The low vesicularity and smooth fracture surfaces are characteristic of hyaloclastic
ash. Vesicle diameters range from 5 to 70 microns, B, Photomicrograph of sideromelane frag-
ments, illustrating the rectangular or polygonal shapes observed in thin section. Low vesicularity
and few microlites are also characteristic of hyaloclastic ash. Dark circles are bubbles in the
mounting medium, c, SEM of sideromelane fragment with surfaces exhibiting conchoidal
fractures. The fragment may have been chipped during or after ejection from the vent, D, Photo-
micrograph of sideromelane fragments. The large fragment in the center contains several
feldspar phenocrysts. Dark circular spots are bubbles in the mounting medium.
NUMBER 12 81
*D
82 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 24
Surtsey, Vestmann Islands, Iceland. (All scales are 100 microns.) A, SEM of blocky sideromelane
fragments with smooth fracture surfaces characteristic of hyaloclastic ash. There is a wide
range of vesicle diameters, B, Photomicrograph of sideromelane fragments exhibiting rectangular
or polygonal shapes. The glass is homogeneous and has no skin similar to the skin on sidero-
melane droplets from magmatic eruptions, c, SEM of a blocky sideromelane fragment. The
vesicles are randomly spaced and are generally far apart, D, SEM of sideromelane fragments
with a wide range of vesicularities. The fragment on the right is atypical of the fragments in
this ash sample.
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84 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 25
Taal, Philippines, A, SEM of blocky, nonvesicular sideromelane fragments. (The scale is 25
microns.) B, Photomicrograph of moderately well-sorted ash consisting of (1) equant sidero-
melane fragments, (2) equant tachylite fragments, (3) clinopyroxene crystals, and (4) feldspar
crystals (~An4-). (The scale is 500 microns.) c, SEM of a feldspar phenocryst coated with
moderately vesicular sideromelane. Parallel grooves and ridges in the crystal fragment are due
to twinning. (The scale is 50 microns.) D, SEM of blocky sideromelane and tachylite fragments.
The two fragments in the foreground may be tachylite. Lath-shaped, twinned feldspar microlites,
with lengths ranging from 5 to 25 microns, are visible on the grain surfaces. (The scale is 50
microns.) E, Photomicrograph of blocky sideromelane fragments probably of hyaloclastic origin.
In contrast with droplets from magmatic eruptions of basaltic liquid, there is no skin on the
ash fragments. (The scale is 100 microns.) F, SEM of blocky sideromelane fragments with
smooth fracture surfaces characteristic of hyaloclastic grains. The slight roughness may be due
to weathering. (The scale is 25 microns.)
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86 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 26
Table Rock Tuff-Ring Complex, Oregon, A, SEM of blocky sideromelane fragments. The freshest
fragment in the upper right center has a very low vesicularity. The grain surface has been
etched by weathering. The other fragments have been altered to palagonite, a mixture of clays,
zeolites, and iron oxides. The older ash (Pleistocene age) is included for comparison with fresh
hyaloclastic ash from Capelinhos and Surtsey (Figures 20 and 21). (The scale is 100 microns.)
B, Photomicrograph of angular sideromelane fragments. The dark rims on each fragment consist
of palagonite and are not chilled skins. (The scale is 100 microns.) c, SEM; closeup of the
etched sideromelane grain in A. Vesicle diameters range from 1 to 10 microns. (The scale is
10 microns.) D, Photomicrograph of blocky sideromelane fragment. (The scale is 100 microns.)
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88 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 27
Kilauea, Hawaii (1924 phreatic eruption) . (All scales are 100 microns.) A, SEM. The ash is
composed of mostly equant blocky basalt fragments. Some have been weathered, B, Photomicro-
graph of the lithic-crystal ash that consists of (1) holocrystalline basalt, (2) altered hyalocrys-
talline basalt fragments, (3) olivine-rich basalt, (4) tachylite, (5) equant olivine crystals,
(6) opaque minerals, (7) an orthopyroxene, (8) tabular, slightly rounded sideromelane frag-
ments with abundant feldspar microlites, and (9) blocky nonvesicular sideromelane fragments
with no vesicles, partly altered to palagonite. c, SEM of vesicular basalt fragment (center) .
Clump of small angular sideromelane and tachylite fragments (left side) .
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90 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 28
Panum Crater, California. A, SEM of a broken pumice fragment containing flattened pipe
vesicles. There are both smooth and conchoidal fracture surfaces. (The scale is 10 microns.)
B, Photomicrograph of shards in the colorless crystal ash. The two largest fragments (upper
left and lower right) are pumiceous, with vesicles 0.5 to 20 microns across (in cross section).
Smaller shards are square or crescent shaped. (The scale is 100 microns.) c, SEM. The largest
fragment is pumice, with subparallel, somewhat curved pipe vesicles. It has been pitted, probably
by weathering. (The scale is 10 microns.) D, SEM of a pumice fragment, with flattened pipe
vesicles similar to the fragment in A. The main difference is the smooth outer surface (on the
upper right), which may be an outer skin. (The scale is 10 microns.) E, Photomicrograph of
well-sorted, colorless shards and pumice fragments. (The scale is 100 microns.) F, SEM of a
colorless ash consisting of sharp, angular, elongated shards. The shards are possibly fragments
of vesicle walls from broken pumice fragments. (The scale is 10 microns.)
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PLATE 29
Sugarloaf Ash, San Francisco Mountains, Arizona, A, SEM. The fragment in the foreground
is a lithic fragment consisting of rhyolite. The two angular fragments in the back are colorless
glass. There are very few vesicles visible in the vitric fragments. (The scale is 50 microns.)
B, SEM of an angular, blocky vitric fragment; most of the grain surfaces are smooth or con-
choidal. (The scale is 20 microns.) c, SEM. Lithic fragments (rhyolite) with rough, irregular
grain surfaces are visible in the foreground. The angular, blocky fragments in the back, which
have smooth grain surfaces, are colorless glass. (The scale is 50 microns.) D, Photomicrograph
of colorless angular shards and pumice in a matrix of fine-grained glass fragments. Most of the
fragments are not vesicular. Those that are vesicular have very low vesicularity. (The scale
is 100 microns.) E, Photomicrograph of a vitric-lithic ash. Most of the colorless fragments are
nonvesicular rhyolitic glass, as in the fine-grained matrix. The large rounded fragment in the
lower center is hyalocrystalline rhyolite. The large colorless fragment at the right is pumice
of moderate vesicularity, with an accretionary rim of fine-grained glass fragments. (The scale
is 500 microns.) F, Photomicrograph of a blocky angular glass fragment similar to the one in c.
It is a matrix of smaller glass fragments. (The scale is 100 microns.)
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PLATE 30
Puu Hou littoral cones, A, SEM of vitric ash consisting of (1) angular blocky glass fragments
formed by rapid chilling of the lava and subsequent contraction and shattering (good example
in upper left center) and (2) broken droplets with fluidal surfaces. Most of the ash exhibits
low vesicularity. (The scale is 100 microns.) B, Photomicrograph of vitric ash. The ash consists
of mostly sideromelane fragments, with a few tachylite grains (black grains in photograph).
The blocky sideromelane fragments contain 2 to 8 percent olivine phenocrysts and up to 20
percent feldspar and pyroxene microlites. (The scale is 500 microns.) c, SEM. The highly
angular sideromelane fragments appear to have been broken from an area between large
vesicles. The smooth fracture surfaces of glass between vesicles is characteristic of hyaloclastic
ash. (The scale is 100 microns.) r>, Photomicrograph of vitric ash. In the center is an angular
sideromelane fragment of hyaloclastic origin, with an olivine phenocryst attached to one side.
Microlites in the glass are randomly oriented. (The scale is 500 microns.) E, SEM of a broken
sideromelane droplet. The smooth curved surface is part of the original droplet surface. (The
scale is 100 microns.) F, Photomicrograph of twisted sideromelane droplets with 2- to 5-micron-
thick skins. (The scale is 100 microns.) G, SEM of hyaloclastic fragment, with vesicles several
hundred microns long. (The scale is 100 microns.) H, SEM of a broken sideromelane droplet
(lower center) surrounded by hyaloclastic fragments. (The scale is 100 microns.)
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H
96 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 31
Sand Hills littoral cones, A, SEM of a sideromelane ash consisting of (1) angular pyramidal
and crescent-shaped grains with very low vesicularities, (2) equant blocky grains with low or
moderate vesicularity, and (3) droplets or broken droplets with moderate vesicularity. (The
scale is 100 microns.) B, SEM of a broken glass droplet. The original outer surface with a small
skin is visible in the upper central part of the fragment. Lumps in the skin are over vesicles
located just below the surface. Fracture surfaces are irregular and, in some places, conchoidal.
(The scale is 100 microns.) c, Photomicrograph of sideromelane ash fragments. On the bottom
is an elongate sideromelane droplet with elongate vesicles. The angular fragments above the
droplet are of hyaloclastic origin. (The scale is 500 microns.) D, Photomicrograph of the edge
of a sideromelane droplet with a thin dark skin. (The scale is 100 microns.) E, SEM of a
pyramidal angular sideromelane fragment of hyaloclastic origin. The smooth fracture surfaces
formed by chilling of the lava and contraction of the cooling glass are unlike the conchoidal
fractures formed by crushing. (The scale is 100 microns.) F, SEM of a broken droplet (center)
with moderate vesicularity. (The scale is 100 microns.)
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PLATE 32
Glass from the Ries Basin, Germany, A, SEM of a colorless glass fragment from the matrix of
a suevite breccia. The fragment is weathered, masking the original grain shape. The broken
outer edge exposes subparallel pipe vesicles. Half of this fragment is nonvesicular. (The scale is
100 microns.) B, Photomicrograph of K-Na feldspar glass, showing vesicles, schlieren, and an
inclusion of quartz glass (Q). Otting quarry (from von Engelhardt and Stoffler, 1968). (The
scale is 100 microns.) c, SEM; closeup of the vitric fragment in A, showing elongate vesicles
with diameters of 2 to 8 microns. (The scale is 10 microns.) D, Photomicrograph of a thin
section of inhomogeneous Ries glass, showing partly melted crystals, rock fragments, and
well-defined schlieren (Horz, 1965) . E, Silhouettes of bombs from the Ries Crater, included for
comparison with the fine-grained fragments (Horz, 1965). The fluidal shapes are similar to
many droplets from basaltic eruptions. (The scale is 20 cm.) F, Photomicrograph of unrecrys-
tallized banded glass from the Ries Basin. Bands are of slightly different compositions. The
inhomogeneity of these glasses is characteristic of glassy ejecta from impact craters (von Engel-
hardt and Stoffler, 1968). (The scale is 100 microns.)
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100 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
PLATE 33
Dial-Pack explosion, A, SEM of the surface of a glass sphere studded with smaller spheres and
droplets. (The scale is 100 microns.) B, Photomicrograph of a thin section through a hollow
glass sphere similar to the one in A. The space on the right is the hollow center; on the left,
the sphere surface. The 400-micron-thick walls consist of moderately vesicular inhomogeneous
glass spheres. (The scale is 500 microns.) c, SEM of glass spheres welded to the surface of a
larger sphere. Nearly all the sphere sizes present in the sample are visible in this photograph.
(The scale is 100 microns.) D, Photomicrograph of a thin section through an oblate glass
spheroid welded to the surface of a larger sphere, similar to that in c. Both spheres are vesicular.
(The scale is 100 microns.) E, SEM of the surface of a large sphere with abundant smaller
spheres imbedded in it. The smaller spheres, which quenched faster, were solid at the time
of collision with the larger sphere. (The scale is 10 microns.) F, Photomicrograph of a thin
section through the edge of a glass sphere, with a smaller sphere imbedded in the surface. (The
scale is 100 microns.) G, SEM of a glass sphere that is unique because of the relatively smooth
suiface which is free of smaller particles imbedded in it. (The scale is 100 microns.) H, SEM
of a deformed glass droplet on the surface of a larger glass sphere. The smaller droplet was
still molten when it collided with the larger sphere, spreading over the surface. (The scale is
10 microns.) i, Photomicrograph of a thin section through a droplet similar to the one in H,
which collided with the larger sphere while it was still molten. (The scale is 100 microns.)
j, Photomicrograph of a thin section through a glass sphere, showing the inhomogeneity of the
glass. Schlieren consist of dark-brown and colorless wisps and bands. There are some vesicles
(light circles) and bubbles in the thin-section mounting media (dark circles) . (The scale is
100 microns.)
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