CIRC. 877

Potential Hazards from

Future Volcanic Eruptions in the

Long Valley-Mono Lake Area,

East-Central California and

Southwest Nevada 

A Preliminary Assessment

Potential Hazards from

Future Volcanic Eruptions in the

Long Valley-Mono Lake Area,

East-Central California and

Southwest Nevada 

A Preliminary Assessment

By C. DAN MILLER, DONAL R. MULLINEAUX, 

DWIGHT R. CRANDELL, and ROY A. BAILEY

GEOLOGICAL SURVEY CIRCULAR 877

7982
United States Department of the Interior

JAMES G. WATT, Secretary

Geological Survey

Dallas L. Peck, Director

First Printing 1982 

Second Printing 1983

Free on application to the Branch of Distribution, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Introduction ............................................ 1

Eruptive products and their effects ............................... 3

Ash falls ............................................ 3

Pyroclastic flows ....................................... 3

Pyroclastic surges ....................................... 5

Lava domes and flows .................................... 5

Floods and mudflows ..................................... 5

Volcanic gases ......................................... 5

Hazard zones ............................................ 7

Hazard zones for eruptions of moderate volume ..................... 8

Hazard zone for an eruption of very large volume .................... 8

Hazard-zone boundaries ................................... 9

References cited .......................................... 10

ILLUSTRATIONS

Page

FIGURE 1. Index map of the Long Valley-Mono Lake area, east-central California and southwest Nevada ...... 2

2. Map of potential volcanic hazards in the central part of the Long Valley-Mono Lake area, east-central

California and southwest Nevada ......................................... 4

3. Potential hazards from air-fall ash ......................................... 6

4. Diagram showing average percentage of time, annually, that winds at six altitudes blow toward wedge-shaped

sectors centered on 16 principal compass directions above Las Vegas, Nevada ............... 7

5. Map showing distribution of Bishop ash beds from eruption at Long Valley caldera ............ 9

in

POTENTIAL HAZARDS FROM VOLCANIC ERUPTIONS IN THE

LONG VALLEY-MONO LAKE AREA,

EAST-CENTRAL CALIFORNIA AND SOUTHWEST NEVADA 

A PRELIMINARY ASSESSMENT

By C. Dan Miller, Donal R. Mullineaux, Dwight R. Crandell, and Roy A. Bailey

INTRODUCTION

Recent earthquakes, ground deformation, and 

increased fumarolic activity in the vicinity of Mammoth Lakes in the southern part of the Long Valley-Mono Lake area of California (fig. 1) have increased the concern over the possibility of a volcanic eruption in the near future, although no one 

can yet reliably predict either that there will be an 

eruption, or the time, scale, or specific site if an 

eruption does occur. This report is a response to 

that increased concern.

The Long Valley-Mono Lake area has been the 

site of volcanic eruptions for millions of years. 

Long Valley itself (fig. 1) is part of a large volcanic 

depression called the Long Valley caldera, which 

formed as a result of colossal eruptions about 

700,000 years ago. Other volcanic activity within 

the last few thousand years included explosive 

eruptions of pumice and formation of lava domes 

from numerous vents along the Inyo and Mono 

chains of volcanoes. The most recent eruptions 

known, from the Inyo chain of vents a short distance north of the community of Mammoth Lakes, 

consisted of steam explosions that ejected 

preexisting rock material about 500 years ago and 

explosive eruptions of rhyolite less than 400 years 

ago.

Earthquake activity in the Long Valley region 

began to increase in 1978. In mid-May, 1980, intense earthquake swarms (Ryall and Ryall, 1980), 

occurred about 10 days before the Mammoth 

Lakes area was shaken by a historically unprecedented series of earthquakes that included four 

of Richter magnitude 6 within a 48-hour period 

(Cramer and Toppozada, 1980). Since that time 

earthquake swarms, accompanied by spasmodic 

tremor, have repeatedly occurred underneath a 

locality referred to as the epicentral site about 3 

km (2 mi) southeast of the community of Mammoth 

Lakes (Ryall and Ryall, 1981; Ryall and Ryall, 

1982). The depths at which earthquakes in these 

swarms originated seem to have become shallower 

since June 1980 (A. Ryall, oral commun., 1982). 

These seismic events are thought to have been 

generated by magma rising under the epicentral 

site (Ryall and Ryall, 1982; R. Cockerham, oral 

commun., 1982).

In October 1980, surveying along U.S. Highway 

395 across the Long Valley caldera revealed that a 

preexisting broad uplift, called a resurgent dome, 

in the western part of the caldera had bulged upward about 25 cm (10 in.) possibly within the previous 2 years (Savage and Clark, in press). Additional geophysical evidence indicates that partially 

molten magma underlies much of that uplift (Hill, 

1976; Steeples and lyer, 1976; Ryall and Ryall, 

1981; Ryall and Ryall, 1982).

In January 1982, increased fumarolic activity 

was first noticed near the Casa Diablo Hot Springs 

about 2 km (1 mi) northeast of the epicentral site 

of the recent earthquakes.

A preliminary interpretation of this evidence is 

that magma beneath the Long Valley caldera 

moved upward at about the time of the May 1980 

swarm of earthquakes. This caused bulging of the
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resurgent dome and opened fractures at depth in 

the southern part of the caldera (R. A. Bailey and 

R. Cockerham, written commun., 1982), which allowed a tongue of magma to move toward the surface beneath the epicentral site. It cannot be determined whether this magma will reach the surface and cause an eruption, or will cool and solidify 

beneath the surface.

This report, revised from U.S. Geological Survey Open-File Report 82-583 (Miller and others, 

1982), describes potential volcanic hazards and 

areas that could be affected by eruptions in the
Long Valley, Inyo Craters, and Mono Craters 

areas. An investigation to provide data for a more 

comprehensive volcanic hazards assessment for 

the Long Valley-Mono Lake area is underway, 

but only partially completed. Thus, this preliminary assessment is based mainly on the results of 

extensive research on the Long Valley volcanic 

system by Bailey and other U.S. Geological Survey scientists (see, for example, Bailey, Dalrymple, and Lanphere, 1976), about 5 weeks of 

fieldwork by Miller, and published reports and unpublished data of other Federal, State, and university scientists.

ERUPTIVE PRODUCTS AND 

THEIR EFFECTS

Future eruptions are most likely to consist of 

one or more of the types of activity that have occurred before in the Long Valley-Mono Lake region. Past eruptions in that region include explosive eruptions that produced chiefly silicic (dacitic 

to rhyolitic) ash falls, pyroclastic flows, and pyroclastic surges of small to large volume, and relatively nonexplosive eruption of silicic lava domes 

and basaltic lava flows. Any of these eruptive 

events could cause floods and mudflows, especially 

if the area adjoining an active vent is covered with 

snow. Volcanic gases are emitted during eruptions, and also during dormant intervals.

ASH FALLS

Volcanic ash and larger fragments are ejected 

upward above a vent by explosive eruptions, 

which may range from blasts that last only a few 

seconds to explosively rapid, continuous rushes of 

fragment-laden gas that continue for hours. Such 

rock fragments can be projected high into the air; 

as winds carry them away, large fragments fall 

close to the vent, whereas the smaller particles 

are carried farther, forming a lobe-shaped blanket 

leading away from the vent. Layers of ash may be 

thick near the volcano but become thinner with increasing distance. Thus, the expectable effects of 

ash are greatest where it is thickest near the volcano, and decrease with increasing distance.

Ash falls generally endanger property more 

than human lives. Ash endangers human health 

chiefly by its effect on respiratory systems. A lesser hazard exists from toxic gases which may accompany the ash. Impact of large rock fragments 

thrown from the vent by explosions can endanger

people and property near an erupting vent, and 

hot rock fragments can start fires. Danger from 

such rock fragments can extend as much as 10 km 

(6 mi) from the source vent. Thick ash accumulations can cause roofs to collapse and, especially if 

wet, can shut off telephone and electric-power service by breaking transmission lines. Lightning 

typically accompanies clouds of ash, and may interrupt telephone, radio, and electrical services 

and start fires. Ash fall can reduce visibility, producing darkness during daylight hours, and halt 

air, rail, and highway traffic; and deposits on the 

ground can block roads. Ash can disable motor vehicles and other machinery by clogging air filters 

and causing rapid wear of moving parts. It can 

also cause short circuits in electrical systems and 

electronic equipment, clog filters in water- and airsupply systems, and incapacitate these and sewer 

systems by plugging collection, treatment, and 

distribution systems with accumulations of ash.

During an ash fall, people generally should stay 

indoors and avoid ash inhalation by breathing 

through commercial dust filters or moistened 

cloths. Eyes should also be protected as much as 

possible. It may be possible, but generally is inadvisable, to attempt to evacuate an area during an 

ash fall. Mechanical equipment can be protected 

by being covered and allowed to remain idle; if 

such equipment is used, filtration of air, water, 

and fuel can reduce the effects of abrasive and corrosive ash.

PYROCLASTIC FLOWS

Pyroclastic flows are relatively high-density 

masses of hot, dry rock fragments mixed with hot 

gases; the flows move like fluids along the ground 

surface at high speed outward from a volcanic 

vent. Such pyroclastic flows commonly reach temperatures of hundreds of degrees Celsius and 

speeds of 50-150 km/hr (30-90 mph). They generally follow valleys or other depressions but can 

have enough momentum to overtop hills or ridges 

in their path. Clouds of hot ash that commonly 

precede or accompany pyroclastic flows may, depending on wind conditions, affect areas as much 

as several kilometers wide adjacent to the margins 

of the flows.

Pyroclastic flows are especially dangerous because of their speed, high temperature, and possible long travel distance. They generally destroy 

life and structures in areas they cross by impact, 

incineration, or burial. Pyroclastic flows moving
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over snow or into water can generate hot 

mudflows, secondary steam explosions, and waves 

in water bodies. The paths of some pyroclastic 

flows that originate on the sides of domes can be 

anticipated, but other pyroclastic flows can be 

caused by the fallback of material in vertical-eruption columns and can move radially outward in 

many or all directions. Because of the speed with 

which pyroclastic flows can be generated and with 

which they can move, the most effective mitigative measure is to evacuate people from zones that 

are likely to be affected.

PYROCLASTIC SURGES

Pyroclastic surges are relatively low-density, 

cloudlike mixtures of rock particles and gases that 

move at high speed outward from volcanic vents. 

Hazards presented by pyroclastic surges include 

severe abrasion, impact by rock fragments, and 

deposition of ash and coarser material. Structures 

can be damaged or destroyed by a surge moving 

along the ground surface at high speed. High temperatures of some surges create an added hazard. 

Pyroclastic surges move at speeds similar to those 

of pyroclastic flows, and can also be lethal to all 

forms of life. The speed of surges is so great that 

escape is not possible once they have been generated, and only windowless, airtight, and fireproof 

structures of substantial strength would protect 

people in the path of a surge. The most practical 

mitigative measure is to evacuate people from 

zones that are likely to be affected.

LAVA DOMES AND FLOWS

Lava domes and flows result from relatively 

quiet eruption of molten rock that piles up over a 

volcanic vent, or flows away as a molten stream. 

Lava domes and flows seldom threaten human life 

directly because their slow rate of movement usually allows people to move out of their path. Furthermore, lava flows typically move along predictable paths determined by local topography. Basalt 

lava flows may reach distances of more than 50 km 

(30 mi) from their sources, but because of their 

greater viscosity, silicic lava extrusions typically 

produce short, thick volcanic domes and flows that 

seldom move as far as 5 km (3 mi).

The principal hazard associated with formation 

of a dome results from pyroclastic flows, and from 

rock fragments thrown out by explosions. The 

flanks of growing domes typically are unstable,

and often collapse to form pyroclastic flows that 

may move outward beyond the dome. During 

periods of active dome growth, areas within a distance of at least 5 km could be endangered by such 

pyroclastic flows, and this distance would progressively increase as a dome grew higher.

FLOODS AND MUDFLOWS

Eruptions at vents in areas covered with snow 

may cause hot mudflows as hot rock debris mixes 

with snowmelt, or floods that may become 

mudflows as they incorporate rock debris. Floods 

and mudflows can threaten people and structures, 

and block evacuation routes along valley floors. 

Because of their high density, mudflows can carry 

large and heavy objects such as vehicles and 

bridges. Reservoirs downvalley from an active 

vent can trap floods and mudflows, but water displaced from them can become a hazard if the reservoirs are already full. For this reason, lowering 

the level of a reservoir such as Lake Crowley to 

accommodate floods and mudflows is advisable if 

an eruption appears to be imminent, and if products of that eruption could melt large volumes of 

snow in the drainage basin above the reservoir. 

General paths of floods and mudflows can be predicted because they follow valleys and other depressions, and people can escape by moving upslope. Those that occur at night or at other times 

of poor visibility are especially dangerous because 

their approach may not be observed. Floods generally move at speeds of less than 25 km/hr (15 mi/ 

hr), but mudflows can move at least as fast as 50 

km/hr (30 mi/hr).

VOLCANIC GASES

Volcanic gases are emitted without rock material from small vents called fumaroles, and they 

generally accompany molten or solid rock fragments expelled during eruptions. Volcanic gases 

usually consist predominantly of steam, accompanied by carbon dioxide and compounds of sulfur 

and chlorine. Minor amounts of carbon monoxide, 

fluorine and boron compounds, ammonia, and 

other compounds are found in some volcanic gases. 

Distribution of volcanic gases is mostly controlled 

by the wind; gases concentrated near a vent rapidly become diluted as they are carried downwind.

Volcanic gases can affect eyes and respiratory 

systems of people and animals and thus endanger 

life and health. Accumulation of heavier-than-air
120°00' 114°

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DISTANCE, IN KILOMETERS

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FIGURE 3. Potential hazards from airfall ash. A, Hazard zones for air-fall ash from recognized potential vent areas in the 

Long Valley-Mono Lake area. Diagonal line and stipple patterns show flowage-hazard zones out to a distance of 20 km (12 

mi) from recognized potential vents, as shown in figure 2. Lines surrounding those areas represent potential ash thicknesses of 20 cm at 35 km (dashed line), 5 cm at 85 km (dotted line), and 1 cm at 300 km (solid line) (8 in. at 22 mi, 2 in. at 53 

mi, and '/2 in. at 185 mi). Hazard from air-fall ash is greatest near source, and decreases as thickness of deposit decreases. 

B, Possible thickness and distance relation for ash of a volume of approximately 1 km3 (Vi mi3) erupted from a vent at the 

north end of the Mono Craters chain, and carried eastward along the double line shown in figure 3A.
gases such as carbon dioxide in depressions can 

suffocate people or animals. Gases can also corrode 

metals and destroy crops and other vegetation. 

Even where dilute, volcanic gases can have a 

noticeable odor and can harm plants many tens of 

kilometers downwind from a vent.

Wilcox (1959) noted that although it is not possible to prescribe complete protective measures, a 

properly fitted industrial gas mask with acid-type 

filter is best for protection from volcanic gases, 

and that where such special equipment is lacking, 

a dampened cloth has been found to be a practical 

expedient. Airtight goggles can lessen effects on 

eyes. Wilcox also recommended renewing the effectiveness of a wet cloth by rinsing, because the 

action of the wet cloth is to trap the acidic gas in 

the moisture of the cloth (Wilcox, 1959, p. 443).

HAZARD ZONES

The location of epicenters of recent earthquakes 

suggests that if an eruption occurs in the near future, the vent is likely to be in the southern part 

of the Long Valley-Mono Lake area. Nevertheless, an eruption might occur instead in some 

other nearby area that has been volcanically active 

in the recent geologic past, especially along the 

Mono Crater and Inyo Crater vent systems. Thus, 

hazard zones (fig. 2) have been drawn around both 

the epicentral site and the Mono-Inyo vent sites.

Although future eruptions of lava domes and 

flows are expectable, explosive eruptions are the 

chief concern. Explosive eruptions that are considered possible in the Long Valley-Mono Lake area 

include steam-blast eruptions that produce no 

magma, eruptions that produce widely variable 

volumes of silicic magma as pumice, and even a 

catastrophic eruption of an immense volume of material such as occurred about 700,000 years ago 

(Bailey and others, 1976; Wood, 1977).

Steam-blast (phreatic) eruptions like those of 

the Long Valley-Mono Lake area are produced 

when rising magma heats subsurface water. They 

may occur without other volcanic activity or may 

be followed by eruptions of magma. Rock fragments thrown out by such explosions could fall as 

far as 10 km (6 mi) from the vent, and windborne 

ash could fall on areas at distances of many tens of 

kilometers. Such steam explosions could also produce pyroclastic surges, which may move outward 

at great speed as far as 10 km (6 mi) from their

source vents. A steam-blast eruption up through a 

lake could also cause large waves, and subsequent 

floods and mudflows. Effects of steam-blast eruptions are expected to be less extensive than those 

from explosive eruptions of magma; thus hazard 

zones for steam-blast eruptions are not differentiated in figure 2.

Figures 2, 3, and 5 depict hazard zones for explosive eruptions comparable to two such eruptions that have occurred at Long Valley in the 

past: (1) explosive eruptions of moderate volume 

(on the order of 1 km3, or x/4 mi3) from the vicinity 

of recently active vents and from the vicinity of 

the epicentral site east of Mammoth Lakes; and (2) 

an eruption of the volume of the catastrophic eruption that occurred about 700,000 years ago, 

originating from the southern part of Long Valley. 

The discussion of hazard-zone maps is followed by 

an explanation of hazard-zone boundaries.

E15

FIGURE 4. Average percentage of time, annually, that winds 

at six altitudes from about 3000 to 16,000 m (10,000 to 53,000 

ft) blow toward wedge-shaped sectors centered on 16 principal compass directions above Las Vegas, Nev. Percentages 

for the same altitudes above Oakland, Calif., west of the 

Sierra Nevada range, are similar. Percentages are rounded 

to nearest whole number. Data from Winds Aloft Summary 

of the Air Weather Service, U.S. Air Force, available from 

the National Climatic Center, Asheville, N.C.
HAZARD ZONES FOR ERUPTIONS OF 

MODERATE VOLUME

HAZARD ZONE FOR AN ERUPTION OF 

VERY LARGE VOLUME

Explosive eruptions of moderate magma volume 

(as much as about 1 km3 , or 1A mi3) at the Mono 

Craters have produced extensive pyroclastic flows 

and ash falls. Pyroclastic flows produced during 

such eruptions of the last 10,000 years, for example, have traveled at least 15 km (9 mi) from their 

source vents. This distance, plus an additional 

margin of safety of 5 km (3 mi), is the basis for the 

20-km-radius flowage-hazard zone shown in figures 2 and 3. This zone has been drawn around 

vents that have been explosively active in the last 

10,000 years and includes areas that might be affected by pyroclastic flows during future eruptions 

of moderate volume. A similar flowage-hazard 

zone extends outward to a distance of 20 km (12 

mi) from a linear area of possible future vents near 

the south margin of the Long Valley caldera. That 

area, defined by frequent earthquakes since May 

1980, begins at the epicentral site of recent earthquake swarms within the caldera and extends 

eastward about 12 km (7 mi) along the south margin of the caldera.

Downwind deposits of ash produced by an explosive eruption of moderate volume from the Mono 

Craters probably could reach thicknesses of at 

least 20 cm (8 in.) at a distance of 35 km (22 mi), 

and 5 cm (2 in.) at 85 km (53 mi) (fig. 3). These estimates of potential ash thicknesses are based on 

deposits of ash from past eruptions at other volcanoes that involved volumes of as much as about 

1 km3 (V* mi3). The anticipated outer limit of ash 

20 cm (12 in.) or more thick is shown in figure 2 at 

a distance of 35 km (22 mi) from all likely sites of 

future vents. Only part of an ash-fall hazard zone 

would probably be affected by any single ash fall; 

the part affected would be determined by the wind 

direction or directions during an eruption. It is not 

possible now to predict wind directions that will 

exist at the time of a future explosive eruption. 

However, records suggest that on an annual basis 

the winds in the Long Valley-Mono Lake area at 

altitudes where most ash is transported, between 

3000 m and 16,000 m (about 10,000 and 52,000 ft), 

blow toward a sector between N. 45° E. and S. 45° 

E. more than 50 percent of the time, and more 

than 80 percent of the winds blow toward some 

easterly direction between due north and due 

south (fig. 4). Areas in these directions from a 

vent thus have a greater chance of being affected 

than do other areas.

The explosive eruption of very large volume 

that occurred at Long Valley about 700,000 years 

ago resulted in immense pyroclastic flows and 

clouds of airborne ash. Pyroclastic flows of hot 

pumice buried an irregular area of at least 1500 

km2 (580 mi2) in and adjacent to the Long ValleyMono Lake area to depths of tens to hundreds of 

meters. One lobe of these pyroclastic flows extended southward down the Owens Valley to a distance of at least 65 km (40 mi) from its source 

area, while others traveled down the San Joaquin 

River and other drainages west of the Sierra 

Nevada crest and may have reached the Central 

Valley of California. The pyroclastic flows probably moved at speeds of several hundreds of 

kilometers per hour, which permitted them to 

cross topographic barriers many hundreds of meters high. The eruption also produced voluminous 

airborne ash that was carried eastward by winds 

across the United States, resulting in ash deposits 

as much as 100 cm (40 in.) thick at a distance of 

120 km (75 mi), 40 cm (16 in.) at 200 km (125 mi), 

and 15 cm (6 in.) at 500 km (300 mi). Lesser but 

appreciable thicknesses probably were deposited 

all across the United States.

The hazard zone shown in figure 5 is based on 

the possibility that as much as 1 m (3.3 ft) of airborne ash could be deposited anywhere within the 

zone and that pyroclastic flows could extend to 

that distance. Devastation from such an eruption 

could be severe to total within any part of the circle shown on the map at distances of as much as 

120 km (75 mi) from the center of the Long Valley-Mono Lake area. As with smaller eruptions, 

the directions of thickest ash fall would be determined by wind directions at the time of the eruption. Even upwind, however, pyroclastic flows of 

hot pumice could completely devastate much of the 

area within 120 km of the vent, especially along 

valleys.

The likelihood of a future eruption as large as 

this cannot be calculated with data now available; 

such an eruption would be much more damaging 

but far less likely than a smaller eruption. An 

eruption of that volume is tentatively regarded as 

much less probable than an eruption involving a 

volume of a few cubic kilometers or less.

A catastrophic eruption of a volume like that of 

700,000 years ago has occurred nowhere in the 

world during historic time, so the kinds and timing

8
of precursory events and the full range of possible 

consequences cannot be anticipated.

HAZARD-ZONE BOUNDARIES

Flowage-hazard zones on the accompanying figures enclose areas that may be affected by future

explosive eruptions of the volume of the two 

events used as models. The outer boundaries of 

the zones are generalized and enclose minimum 

areas that would be endangered by eruptions like 

those of the two models used. Within these zones, 

relative hazard generally decreases with increas125°00' 120°00' 115°00' 110°00' 100°00' 95°00'

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FIGURE 5. Distribution of Bishop ash beds from eruption at Long Valley caldera (LV), as shown by Izett, Obradovich, and 

Mehnert (1982). Pattern encloses sites of identified Bishop ash beds; ash must also have been deposited beyond the extent 

shown (Izett and others, 1982, p. 5). Thickness of ash beds judged to be unreworked at distances of 550 km (340 mi) and 820 

km (510 mi) from the source vent suggests that the Bishop ash at the easternmost boundary shown was less than 1 cm (¥2 in.) 

thick. Circle at 120 km (75 mi) from the center of the Long Valley caldera encloses area subject to accumulation of 1 m or 

more of airfall ash downwind during a future eruption similar to that which produced the Bishop ash. Hot pyroclastic flows 

could occur anywhere within this area and could extend even farther down valleys that head in this area.
ing distance from a vent and with increasing 

height above valley floors or basins. The positions 

of the hazard-zone boundaries do not reflect topographic relief, because (1) pyroclastic flows and 

surges can overtop topographic barriers in their 

paths, (2) associated clouds of ash can affect areas, 

including high ground, many kilometers wide adjacent to pyroclastic flows, and (3) pyroclastic flows 

travel farthest down valleys and along other depressions, but the maximum distances to which 

they might extend are not known.

Thus, the outer boundaries of flowage-hazard 

zones shown in figures 2 and 3 are smooth curved 

lines that disregard topography and should be interpreted only as a "generalized" outer limit of one 

level of hazard. It should be understood that flowage phenomena may extend beyond the zone 

boundary, and possibly even reach onto adjacent 

topographically high areas.

Ash-hazard zones are not assigned zone boundaries comparable to those for flowage hazards. 

Hazardous flowage events have geographic limits, 

even though they may be difficult to predict. No 

comparable limits exist for the extents of ash-fall 

deposits, which simply diminish with increasing 

distance downwind. Moreover, people a d different kinds of structures, machines, and vegetation 

have different tolerances for ash. An ash fall that 

might not endanger a healthy person could seriously affect a person with breathing problems. 

Thus, the graph (fig. 3B) shows potential ash 

thicknesses at various distances from possible 

vents (compare fig. 3A), and can be used to anticipate possible effects on people or various kinds of 

property and vegetation. Descriptions of some of 

the effects that resulted from the 1980 eruptions of 

Mount St. Helens have been published. (See, for 

example, Warrick and others, 1981; Schuster, 

1981.)

REFERENCES CITED

Bailey, R. A., Dalrymple, G. B., and Lanphere, M. A., 1976, 

Volcanism, structure, and geochronology of Long Valley 

Caldera, Mono County, California: Journal of Geophysical 

Research, v. 81, no. 5, p. 725-744.

Cramer, C. H., and Toppozada, T. R., 1980, A seismological 

study of the May 1980 and earlier earthquake activity near 

Mammoth Lakes, California, in Sherburne, R. W., ed., 

Mammoth Lakes, California earthquakes of May 1980: 

California Division of Mines and Geology Special Report 

150, p. 91-130.

Hill, D. P., 1976, Structure of Long Valley Caldera, California, 

from a seismic refraction experiment: Journal of Geophysical Research, v. 81, no. 5, p. 745-753.

Izett, G. A., Obradovich, J. D., and Mehnert, H. H.,1982, The 

Bishop ash bed and some older closely related ash beds in 

California, Nevada, and Utah: U.S. Geological Survey 

Open-File Report 82-584, 60 p.

Miller, C. D., Crandell, D. R., Mullineaux, D. R., Hoblitt, R. 

P., and Bailey, R. A., 1982, Preliminary assessment of potential volcanic hazards in the Long Valley-Mono Lake 

area, east-central California and southwest Nevada: U.S. 

Geological Survey Open-File Report 82-583.

Ryall, A., and Ryall, F., 1980, Spatial-temporal variations in 

the seismicity preceding the May 1980, Mammoth Lakes, 

California earthquakes, in Sherburne, R. W., ed., Mammoth Lakes, California earthquakes of May 1980: California Division of Mines and Geology Special Report 150, p. 

27-40.

Ryall, A., and Ryall, F.,1981, Attenuation of P and S waves in 

a magma chamber in the Long Valley caldera, California: 

Geophysical Research Letters, v. 8, no. 6 p. 557-560.

Ryall, F., and Ryall, A., 1982, Propagation effects and seismicity associated with magma in Long Valley caldera, eastern 

California: Earthquake Notes, v. 53, no. 1, p. 46-47.

Savage, J. C., and Clark, M. M., 1982, Magmatic resurgence in 

Long Valley Caldera, California-Possible cause of the 1980 

Mammoth Lakes earthquakes: Science [in press].

Schuster, R. L.,1981, Effects of the eruptions on civil works 

and operations in the Pacific Northwest, in Lipman, P. W., 

and Mullineaux, D. R., eds., The 1980 eruptions of Mount 

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U.S. GOVERNMENT PRINTING OFFICE: 676-041/16 1983

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