SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES • NUMBER 12

An Atlas of Volcanic Ash

Grant Heiken

APR 1 8

SMITHSONIAN INSTITUTION PRESS

City of Washington

1974
ABSTRACT

Heiken, Grant. An Atlas of Volcanic Ash. Smithsonian Contributions to the

Earth 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 composition

and 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 magmatic gases.

The morphology of ash particles from magmatic eruptions of high-viscosity

magma is governed primarily by vesicle density and shape. The vitric ash particles 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 contributions 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 particles are present in the literature, mostly as thinsection descriptions. Shard shapes are rarely described 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 morphology 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 standard laboratory techniques, to determine if there

is a relation between the type of eruption, the

magma composition, and the ash particle morphology.

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 classification of volcaniclastic fragments by Fisher (1961)

(Plate 1A), used in conjunction with a compositional classification set up by Cook (1965) (Plate

IB).

For brevity, each petrographic mode is summarGrant 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 morphologic features studied here with scanning electron microscope can be identified with standard

microscopes.

ASH FORMATION

There are two basic mechanisms of ash formation: (1) by exsolution and expansion of gases in

a magma, resulting in the froth losing its coherence as it approaches the ground surface (magmatic eruptions), and (2) by chilling of a magma

rising toward the ground surface on contact with

ground or surface water (hydrovolcanic or phreatomagmatic 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 oversaturation developed, cause of oversaturation, viscosity, surface 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 Vulcanian 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 dependent 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 viscosity, 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 highviscosity magma (rhyolitic, dacitic, and some andesitic magmas) is entirely dependent on the shape

of vesicles in the rising magma before disintegration. 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 possible 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 hydrovolcanic (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 fragmentation 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 providing very useful information and ash samples:

W. I. Rose, Dartmouth University; Oliver Kola,

Anchorage, Alaska; Arturo Alcarez, Phillippine

Commission on Volcanology; K. R. Everett, Institute 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, University of St. Andrews, Scotland; Mike Sheridan, Arizona State University; S. Thorarinsson, Museum

of Natural History of Iceland; the Portuguese Geological Survey; David Roddy, U.S. Geological Survey; J. Healy, and C. P. Wood, New Zealand

Geological Survey; W. Melson, Smithsonian Institution; Roald Fryxell of Washington State University, R. Funiciello of the University of Rome,

and Floyd McCoy, Woods Hole Oceanographic

Institute. Special thanks go to R. V. Fisher, University 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 microscope 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 southsouthwest 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) droplets, 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 Acatenango, another volcano adjacent to Fuego.

Petrography: This vitric ash is of basaltic composition. 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. Comminuted, irregularly shaped ash fragments are produced 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 fountaining 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 tachylite fragments (Plate 4). The droplets have smooth

botryoidal or lumpy outer surfaces, broken by depressions 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 fountaining).

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, consisting of mostly broken porphyritic, pale brown

(sideromelane) droplets, with very low vesicularities (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 crystals (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 exhibit 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 vesicularity. The shards are mostly blocky fragments,

with scalloped edges where the grain surface consists of broken vesicle walls (30- to 150-microndiameter 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 eruption 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 tachylite, 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 surfaces 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 occurred in 1959. The samples were collected 2100 m

southwest of the vent.

Petrography: The sideromelane droplets contain 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 surfaces were generally broken over some of the outermost 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 tapering 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 strombolian 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 composition 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 microlites of any kind. The mode is 100 percent sideromelane. (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 latticeshaped 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, sideromelane 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 American 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 phenocrysts. 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 intermittent ash eruptions and lava fountaining (strombolian), 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 elongate droplets are sometimes twisted about the long

axis. The ends may taper to a point but are generally broken (Plates 12A, 12B). Tachylite grains

are similar in shape to the tabular, broken sideromelane 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 plagioclase 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 vesicularity. Most of the <50|x diameter hairs are nonvesicular, 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-microndiameter 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 surface 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 separate 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 mechanical disintegration of the glassy crust of the September 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 vesiclewall 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 possible 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 (written communication, 1972) has examined the "ashflow" 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 northeast 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 communication).

Petrography: The lithic-vitric ash consists of

fragments of porphyritic andesite; mudstone;

medium-crystalline pyroxene-hypersthene andesite;

tachylite; feldspar-rich andesite; crystals of andesine, 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 andesitic 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 compounds. 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 hydrovolcanic and is a mixture of magmatic and hyaloclastic

ashes.

MERAPI, INDONESIA.—The eruption began 10 October 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, consisting 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 plagioclase; 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 component is dominant in this sample. As in the

Merapi ash, there is an abundance of thin, elongate, pointed glass shards (Plate 17), the product

of finely comminuted pumice. Larger glassy particles 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, gasrich 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. Krakatau 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 description from a report on the eruption of Krakatau 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 possibly be classified as vitric, with abundant microlites and phenocrysts), plagioclase (An43), and

quartz crystals. Most vesicles are irregular, flattened 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 vesicular 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 disintegration 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 compositions). 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 consists of small, elongate pumice fragments (Plate

20). The highly vesicular fragments contain elongate, 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 common 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 eruption 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 included 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 micrometers long with very angular shapes. Shards l\i100[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 particles 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 particles, slightly curved along the long axis. These

are vesicle walls from the junction of three adjacent 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 Tanzania, 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 volcano is a dominantly pyroclastic cone with interbedded 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 distributed 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 carbonate (trona) with crystals of nepheline, pyroxene, 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 mineral fragments (Plates 22), including perfect euhedral (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 (phreatomagmatic) eruptions in a shallow marine environment (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 primarily 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 crystal 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 characterized by violent phreatomagmatic eruptions.

Steam was generated when the seawater rushed into

the vent, resulting in vertical and base-surge eruption 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 sideromelane 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 sideromelane fragments (Plate 24) similar to the ash

particles from Capelinhos. Most of the fragments

are blocky and nearly equant. As in the Capelinhos 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 eruptions (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 fragments, equant tachylite fragments (these may be

from underlying, older ash deposits), augite crystals, 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 Surtsey and Capelinhos. The main ash component consists 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 fragments 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 tuffring 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 (phreatomagmatic) eruptions. The ash forms very well-bedded

tuff rings around the crater. The sample was collected 1 km from the vent of ring 2 of the complex.

Petrography: The sample is composed of lightbrown sideromelane, with thin rims of orangebrown 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 petrographically 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 materials, an enormous phreatic eruption was caused.

The eruption lasted 17 days, resulting in the collapse 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 weathering 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 components are nearly equal. Crystal components include sanidine, plagioclase, orthopyroxene, hornblende, 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, ARIZONA.—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 eruption (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 northeast flank of the tuff ring.

Petrography: This sample of rhyolitic lithiccrystal ash consists of mostly colorless shards and

pumice fragments containing 5 to 30 percent subparallel 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 fragments 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 vesicularity.

Pumice fragments, most of which are less than

400 microns across, contain poorly developed ellipsoidal 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 explosions 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 conversion 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 phenocrysts, (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 vesiculation 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) scalloped sideromelane fragments with abundant

vesicles; (2) drawn sideromelane glass with small

vesicles, elongate shapes, and fluidal edges (frozen

droplets); and (3) irregular or equant sideromelane fragments with few or no vesicles (Fisher,

1968). (95.1:0:4.9:0)

Morphology: This ash is the most easily characterized 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 roughsurfaced fragments of tachylite and sideromelane

flow crust (Plate 30).

The well-developed vesicularity near the flow

top accounts for the oddly shaped hyaloclastic component 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 unquenched 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, Kilauea, reached the sea. The sample is from the

cone.

Petrography: The ash consists of mostly sideromelane 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 hyaloclastic fragments. (97.7:0:2.3:0)

Morphology: The morphology of the ash fragments (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, Germany, 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 fragments. Phases contained in the fladen include diaplectic 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 explosion 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 quenching (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 involved 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 (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

(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 sideromelane 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 consisting 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 hydrovolcanic eruptions is controlled by thermal stresses

within the chilled magma, which result in fragmentation 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 isolated volcanic ash samples from stratigraphic sections 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. Baltimore: 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 Implications. 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 Mineralogie 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 Geological 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 Volcano, 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]. Geological 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 Volcanoes of the World. 271 pages. Naples: International 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. Bulletin Volcanologique, 35:303-317.

Wentworth, C. K.

1938. Ash Formation of the Island of Hawaii. Special Report 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 University 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 concentrations. 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 heating under vacuum. The analytical technique employed was a combined thermal analysis-mass

spectrometric procedure described previously (Gibson and Johnson, 1971, 1972; Gibson, 1972; Gibson

and Moore, 1972). A Mettler recording vacuum

thermoanalyzer interfaced to a Finnigan 1015 quadrupole 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 rapidly and without requiring gas transfer procedures.

Sample sizes ranged from 20 mg for volatile rich

ashes to 200 mg for ash samples which were depleted 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 sample'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 measured with calibrated platinum/platinum-10 percent rhodium thermocouples located at the base of

the platinum sample crucibles. Spectra were obtained every 5°C during the heating cycle. Reproducible 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 assumption 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 Carleton 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 weightloss data has been calculated from the thermograms 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 concentration 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 numbers 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 System and Its Application to the Evolved Gas Analysis 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: Massachusetts 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; al l

are highly vesicular.

Smooth, fluidal surfaces broken by smoothlipped vesicle cavities (these broke while

the surface was stil l 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 al l are generally

present; the vitri c component includes

colorless glass shards and pumice fragments; generally containing oriented

microlites; lithi c fragments include

andesite of varying textures and stages

of alteration and igneous and sedimentary xenoliths; broken crystals of plagioclase, 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 elongate 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 generally equant; the surface is entirely

dependent on the texture and fracture

of the rock type; some of the fragments 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 lithi c (rhyolitic or xenolithic ) 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 dependent on vesicle shape) with thin

vesicle walls; curved, Y-shaped, or fla t

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 lapill i 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 carbonate are generally concentrated

in depressions in the grain surfaces.

B. Hydrovolcanic[Phreatomaqmatic] eruptiorst

C. Ash-size vitri c particles of

meteorite impact origin

Manna type Rhyolitic Basaltic (littoral) 5

Volcanic features associated 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; generally free of all crystals except phenocrysts;

the lithic component of some ashes is dependent on the stratigraphy of rocks underlying the maars and the amount of magma

reaching the surface.

SiO?, 45 to 47 percent

Ti1 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 microlites or contains very few microlites.

SiO2, 75.4 percent

Fe as Fe203, 0.9 percent

Al 2 03 , 13.5 percent

Sharply pointed elongate shards and

fla t elongate pumice fragments.

faces of each arlin the ves'cTe Ltul 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

lithi c fragments.

2

- Sideromelane glass fragments with few

vesicles; these may be blocky or crescen t shaped . th e shap e my b e 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 different 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 broken) a few microns to several

centimeters in diameter; abundant

smaller spheres, droplets, and

rQc k fragment s ar e welde d t 0 tn e

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 i t reaches the surface, resulting in (1) large-scale ash eruption (Plinian, Vulcanian, or Pelean) with resulting ash falls and ash

flows; high-viscosity lavas; associated lahars or volcanic mudflows i f the eruption is into a crater lake

or is accompanied by rainstorms; and (2) lava fountaining 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+

H2OCl

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+

H2OCl

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 VolcanoPhilippines 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, California 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

TABL E

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

c

o

TJ

C

3

J3

O

-40-(xl00)

-34-(xl00)

-64-(xl00)

-44-(xl00)

20 -

200 4 0 0 600 800

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

c

o

c

3

O

H 2 - 2 - (x 100)

H2O - 18- (x 10)

CO2 "44 - (x 100)

CO, N2 ~ 28- (x 10)

Ar - 40- (x 100)

H2S - 32- (x 100)

2 0 0 4 0 0 600 800 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

u

1C

3

Q

a

a, 40

>Kelat

COS

H2S

" so2

HF

H 2 O - 18

C O 2 - 44 - (x 10)

CO, N 2 - 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

c

o

"0

c

3

60

/CO 2

40

20 H 2 O

200 400

I i i r

600 800

Temperature, °C
24 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

100

Sample wt 150.82 mg

80

c

a

C

3

_Q

O

ex.

60

40

20

161 m

H2 - 2 - (x 100)

H 2O- 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

c

o

"D

C

3

JQ

O

6 0

4 0

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

2 0 0 4 0 0 6 0 0 8 0 0

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 decomposition. 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

m m ' 173 m

CM CO •

I I

co2l I

80

H 2 - 2 - (xlOO)

H2O - 18 - (xl)

CO2 - 44 - (xlO)

H2S - 34 - (xlOO)

SO2 - 64 - (xlOO)

C

° 2 ,'CO2

I!

c

o

c

3

_Q

D

QC

60

2 0 0 400 600 800

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)

- 1 8 -(x 10)

80

CO2 - 44 - (x 100) —

CO - 28 -(x 100)

H2S - 34 - (x 100)

SO2 - 64 - (x 100)

c

o

-o

c

3

D

60

138 m

\co2

200 4 0 0 6 0 0 800

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

c

o

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

2 0 0 4 0 0

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

c

o

-o

c

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)

8 0

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 volatilerich 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

c

o

•D

C

3

_Q

a

60

40

20

137 m

H 2

H 2 O

co2

CO, N 2

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 decomposition 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)

c

o

c

3

.a

o

CO, N 2 - 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

c

o

TJ

C

3

JQ

O

60

40

20 -

- (x 100)

- (x 10)

- (x 100)

. (x 10)

- (x 100)

C O 2 |

.—— *

H2O

H 2

CO, N 2

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

c

o

-0

c

3

.0

a

_0

a:

60

40

20 -

KKN'.K

H2OJ

f

I

\ A

v \

Sample wt 197.67 mg

195 m

H 2 - 2 - (x 100)

H2O - 18 - (xlO)

CO2 - 44 - (xlOO)

H2S -34 - (x 100)

SO2 -64 - (x 100)

2 0 0 4 0 0 6 0 0 8 0 0 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.)
NUMBE

R 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.)
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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, Photomicrograph of an angular tachylite fragment (submicrocrystalline basalt). These fragments

rarely have rounded fluidal edges.
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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.)
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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.)
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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-microndiameter Pele's hair, with a ribbed surface. Each rib is over an elongate vesicle. Adhering to the surface are 1- to 2-mirconthick, 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 vesicular grains have abundant ribs parallel to the long axis. (Scale is 61 microns.)
5 0 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 (collapse 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.)
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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.)
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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.)
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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.)
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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.)
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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.)
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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.)
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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 pyroxenehypersthene 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.)
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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 characteristic 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.)
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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.)
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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.
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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.)
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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 triangular 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.)
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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.)
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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.)
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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 fragments, 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, Photomicrograph of sideromelane fragments. The large fragment in the center contains several

feldspar phenocrysts. Dark circular spots are bubbles in the mounting medium.
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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 sideromelane 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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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 sideromelane 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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8 6 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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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, Photomicrograph of the lithic-crystal ash that consists of (1) holocrystalline basalt, (2) altered hyalocrystalline basalt fragments, (3) olivine-rich basalt, (4) tachylite, (5) equant olivine crystals,

(6) opaque minerals, (7) an orthopyroxene, (8) tabular, slightly rounded sideromelane fragments 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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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 conchoidal. (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-micronthick 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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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 unrecrystallized 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 Engelhardt and Stoffler, 1968). (The scale is 100 microns.)
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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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U.S. GOVERNMENT PRINTING OFFICE: 1973 546-357/5