Steam Explosions, Earthquakes, and Volcanic Eruptions—

What’s in Yellowstone’s Future?

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2005-3024

2005

U.S. GEOLOGICAL SURVEY and the NATIONAL PARK SERVICE—OUR VOLCANIC PUBLIC LANDS

Yellowstone, one of the world’s 

largest active volcanic systems, 

Midway Geyser Basin in Yellowstone National Park appears otherworldly 

beneath stormy skies. In the background, steam vigorously rises from the hot 

Each year, millions of visitors come 

to admire the hot springs and geysers of 

Yellowstone, the Nation’s fi rst national 

park. Few are aware that these wonders 

are fueled by heat from a large reservoir 

of partially molten rock (magma), just 

a few miles beneath their feet. As this 

magma—which drives one of the world’s 

largest volcanic systems—rises, it pushes 

up the Earth’s crust beneath the Yellowstone Plateau.

Stresses in the crust produce movements 

on faults, causing earthquakes to occur. 

Thousands of small quakes are recorded 

each year by the seismographic network 

of the Yellowstone Volcano Observatory 

(YVO), a partnership of the U.S. Geological Survey (USGS), the University of Utah, 

and Yellowstone National Park. Faults and 

fractures also allow surface water to penetrate to depth and become heated, rising 

again to produce hydrothermal (hot water) 

features, such as geysers. Steam and hot 

water carry huge quantities of thermal energy to the surface from the magma chamber below. Continuing up-and-down ground 

motions on the Yellowstone Plateau refl ect 

the migration of both hydrothermal fl uids 

and magma below the surface.

Ground motions, earthquakes, and hydrothermal activity are all current manifestations of volcanic activity at Yellowstone. 

In the not-so-distant geologic past, Yellowstone has produced many major volcanic 

eruptions, which have repeatedly reshaped 

its natural wonders.

Caldera-Forming Eruptions

The Yellowstone region has produced 

three exceedingly large volcanic eruptions 

in the past 2.1 million years. In each of 

these cataclysmic events, enormous volumes of magma erupted at the surface and 

into the atmosphere as mixtures of red-hot 

pumice, volcanic ash (small, jagged fragments of volcanic glass and rock), and gas 

that spread as pyroclastic (“fi re-broken”) 

fl ows in all directions. Rapid withdrawal 

of such large volumes of magma from the 

subsurface then caused the ground to collapse, swallowing overlying mountains and 

creating broad cauldron-shaped volcanic 

depressions called “calderas.”

The fi rst of these caldera-forming 

eruptions 2.1 million years ago created 

a widespread volcanic deposit known as 

the Huckleberry Ridge Tuff, an outcrop of 

which can be viewed at Golden Gate, south 

of Mammoth Hot Springs. This titanic 

event, one of the fi ve largest individual 

volcanic eruptions known anywhere on the 

Earth, formed a caldera more than 60 miles 

(100 km) across.

waters of Grand Prismatic Spring, known for its rainbow colors produced by thermophilic (“heat loving”) organisms. Grand Prismatic is the largest hot spring in Yellowstone and the third largest in the world. This and 

other hydrothermal (hot water) features are among the main attractions for visitors to the park (inset photo). 

These features are fueled by heat from a large reservoir of partially molten rock (magma), just a few miles 

beneath Yellowstone, that drives one of the world’s largest volcanic systems. (Photograph courtesy of Robert 

Fournier; inset courtesy of Susan Mayfi eld.)

has produced several giant volcanic 

eruptions in the past few million 

years, as well as many smaller eruptions and steam explosions. Although 

no eruptions of lava or volcanic ash 

have occurred for many thousands of 

years, future eruptions are likely. In 

the next few hundred years, hazards 

will most probably be limited to ongoing geyser and hot-spring activity, 

occasional steam explosions, and 

moderate to large earthquakes. To 

better understand Yellowstone’s 

volcano and earthquake hazards and 

to help protect the public, the U.S. 

Geological Survey, the University of 

Utah, and Yellowstone National Park 

formed the Yellowstone Volcano Observatory, which continuously monitors activity in the region.
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Yellowstone is home to one 

of the world’s largest active 

volcanic systems. Cataclysmic 

eruptions in the past few million 

years created huge volcanic 

depressions called “calderas.” 

The youngest, the Yellowstone 

Caldera, was formed 640,000 

years ago. Since then, about 80 

A similar, smaller but still huge eruption occurred 1.3 million years ago. This 

eruption formed the Henrys Fork Caldera, 

located in the area of Island Park, west of 

Yellowstone National Park, and produced 

another widespread volcanic deposit called 

the Mesa Falls Tuff.

The region’s most recent caldera-forming eruption 640,000 years ago created the 

35-mile-wide, 50-mile-long (55 by 80 km) 

Yellowstone Caldera. Pyroclastic fl ows from 

this eruption left thick volcanic deposits 

known as the Lava Creek Tuff, which can 

be seen in the south-facing cliffs east of 

Madison, where they form the north wall 

of the caldera. Huge volumes of volcanic 

ash were blasted high into the atmosphere, 

and deposits of this ash can still be found in 

places as distant from Yellowstone as Iowa, 

Louisiana, and California.

Each of Yellowstone’s explosive calderaforming eruptions occurred when large 

volumes of “rhyolitic” magma accumulated 

at shallow levels in the Earth’s crust, as little 

as 3 miles (5 km) below the surface. This 

highly viscous (thick and sticky) magma, 

charged with dissolved gas, then moved 

upward, stressing the crust and generating 

earthquakes. As the magma neared the surface and pressure decreased, the expanding 

gas caused violent explosions. Eruptions of 

rhyolite have been responsible for forming 

many of the world’s calderas, such as those 

at Katmai National Park, Alaska, which 

formed in an eruption in 1912, and at Long 

Valley, California.

If another large caldera-forming eruption 

were to occur at Yellowstone, its effects 

would be worldwide. Thick ash deposits 

would bury vast areas of the United States, 

and injection of huge volumes of volcanic 

gases into the atmosphere could drastically 

affect global climate. Fortunately, the Yellowstone volcanic system shows no signs 

that it is headed toward such an eruption. 

The probability of a large caldera-forming 

eruption within the next few thousand years 

is exceedingly low.

Lava Flows

More likely in Yellowstone than a large 

explosive caldera-forming eruption is erup-

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tion of a lava fl ow, which would be far less 

devastating. Since Yellowstone’s last calderaforming eruption 640,000 years ago, about 

30 eruptions of rhyolitic lava fl ows have 

nearly fi lled the Yellowstone Caldera. Other 

fl ows of rhyolite and basalt (a more fl uid variety of lava) also have been extruded outside 

the caldera. Each day, visitors to the park 

drive and hike across the lavas that fi ll the 

caldera, most of which were erupted since 

160,000 years ago, some as recently as about 

70,000 years ago. These extensive rhyolite 

lavas are very large and thick, and some cover as much as 130 square miles (340 km2

), 

twice the area of Washington, D.C. During 

eruption, these fl ows oozed slowly over the 

surface, moving at most a few hundred feet 

per day for several months to several years, 

destroying everything in their paths.

Today, most of the landforms within the 

Yellowstone Caldera refl ect the shapes of 

these young lava fl ows. Cliffs surrounding 

the Upper Geyser Basin near Old Faithful 

Geyser are the cooled steep fl ow fronts of 

eruptions of rhyolite (thick, sticky 

lava) and basalt 

(more-fl uid lava) 

have occurred. The 

caldera’s interior 

is largely covered 

by rhyolites, most 

erupted in the 

past 160,000 years. 

Large hydrothermal (steam)-explosion craters formed 

in the past 14,000 

years are located 

near Yellowstone 

Lake and in major 

geyser basins. Recent earthquakes 

(1973 to 2002) were 

concentrated 

between Hebgen 

Lake and the Norris 

Geyser Basin and 

along faults. 

VOLCANIC HISTORY AND RECENT SEISMIC ACTIVITY IN THE YELLOWSTONE REGION
3

This house fell into Hebgen Lake during the 1959 earthquake and 

fl oated along the shore until it came to rest here. The owner of the 

house, then-70-year-old Mrs. Grace Miller, escaped only after kicking out her front door and leaping a 5-foot-wide ground crack as her 

house dropped into the lake. (USGS photograph by J.B. Hadley.)

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Earthquakes

From 1,000 to 3,000 earthquakes typically occur each year within Yellowstone 

National Park and its immediate surroundings. Although most are too small to be felt, 

these quakes refl ect the active nature of the 

Yellowstone region, one of the most seismically active areas in the United States. Each 

year, several quakes of magnitude 3 to 4 are 

felt by people in the park. 

Although some quakes are caused by 

rising magma and hot-ground-water movement, many emanate from regional faults 

related to crustal stretching and mountain 

building. For example, major faults along 

the Teton, Madison, and Gallatin Ranges 

pass through the park and likely existed 

long before the beginning of volcanism 

there. Movements along many of these 

faults are capable of producing signifi cant 

earthquakes.

The most notable earthquake in Yellowstone’s recent history occurred in 1959. 

Centered near Hebgen Lake, just west 

of the park, it had a magnitude of 7.5. 

This quake caused $11 million in damage 

(equivalent to $70 million in 2005 dollars) 

and killed 28 people, most of them in a 

landslide that was triggered by the quake.

Geologists conclude that large earthquakes like the Hebgen Lake event are unlikely within the Yellowstone Caldera itself, 

because subsurface temperatures there are 

high, weakening the bedrock and making it 

less able to rupture. However, quakes within 

the caldera can be as large as magnitude 

6.5. A quake of about this size that occurred 

in 1975 near Norris Geyser Basin was felt 

throughout the region. 

Even distant earthquakes can affect 

Yellowstone. In November 2002, the magnitude 7.9 Denali Fault earthquake struck 

central Alaska, 1,900 miles (3,100 km) 

northwest of Yellowstone. Because this 

quake’s energy was focused toward the active Yellowstone volcanic and hydrothermal system, it triggered hundreds of small 

earthquakes there. The region’s hydrothermal system is highly sensitive to quakes 

and undergoes signifi cant changes in their 

wake. Earthquakes may have the potential 

to cause Yellowstone’s hot-water system 

to destabilize and produce explosive hydrothermal eruptions.

Hydrothermal Explosions

The large magma reservoir beneath Yellowstone may have temperatures higher 

than 1,475°F (800°C), and the surrounding 

rocks are heated by it. Because of this, the 

average heat fl ow from the Earth’s interior 

at Yellowstone is about 30 times greater 

once-slow-moving rhyolite lavas. Some 

narrow ridges and valleys on the CanyonNorris road are corrugations on the surface 

of a 110,000-year-old rhyolite fl ow. These 

roughly concentric ridges formed as the 

thick, pasty lava slowly oozed northeastward, wrinkling its surface. Within the caldera, rivers and streams commonly occupy 

the gaps between individual lava fl ows, and 

springs emerge at the edges of fl ows.

Any renewed volcanic activity at Yellowstone would most likely take the form of such 

mainly nonexplosive lava eruptions. An eruption of lava could cause widespread havoc in 

the park, including fi res and the loss of roads 

and facilities, but more distant areas would 

probably remain largely unaffected.

Since its last cataclysmic volcanic eruption 640,000 

years ago, the Yellowstone region has had about 40 

eruptions of slow-moving lava fl ows of rhyolite (a 

variety of molten rock that is thick and sticky). Some 

of these fl ows cover more than 100 square miles, and 

many are very thick, like this approximately 180,000-

year-old rhyolite fl ow exposed at Obsidian Cliff. 

Although no lava has been erupted at Yellowstone 

for 70,000 years, future such eruptions are likely to 

occur. (USGS photograph by Robert Christiansen.) 

Seismogram of the 1959 magnitude 7.5 

Hebgen Lake earthquake recorded at 

Butte, Montana, about 100 miles from 

the epicenter.

The Yellowstone National Park region produces about 

2,000 earthquakes each year. Most of these quakes are 

too small to be felt, but they refl ect the active nature of 

the region, one of the most seismically active areas in 

the United States.

The most powerful earthquake in Yellowstone’s recent 

history occurred in 1959. This quake was centered near 

Hebgen Lake, just west of the park, and had a magnitude 

(M) of 7.5. The Hebgen Lake earthquake killed 28 people—26 in a huge landslide triggered by the quake—and 

caused $11 million in damage (about $70 million in 2005 dollars). Numerous structures 

and roads in the region were severely damaged when hillsides collapsed, gaping 

cracks opened in the ground, and large blocks of rock were displaced. 

The Hebgen Lake quake caused widespread changes in Yellowstone—roads 

were closed throughout the area, some geysers stopped erupting, and others were 

newly formed or came back to life after years of dormancy. Also, the Old Faithful 

Inn was strongly shaken—pipes broke, a chimney collapsed, and the inn had to 

be evacuated. 

Although quakes of this magnitude are rare in the Yellowstone region, they are 

certain to occur in the future. To better understand this hazard and help protect the 

public, scientists of the Yellowstone Volcano Observatory (YVO) continually monitor 

the region’s seismic activity.

EARTHQUAKES IN THE YELLOWSTONE REGION
4

than that typical for areas elsewhere in the 

northern Rocky Mountains. As snowmelt 

and rainfall seep deep into the ground, they 

can absorb enough of this heat to raise the 

temperature of the ground water close to 

the boiling point. Geyser basins and other 

thermal areas in Yellowstone National Park 

are places where hot ground water has 

risen close to the surface. Research drilling at Yellowstone in the 1960s confi rmed 

that the ground water beneath many of the 

park’s thermal areas is very hot. At Norris 

Geyser Basin, water temperatures as high 

as 460°F (238°C) were recorded at depths 

of only 1,090 feet (332 m).

Because the boiling point of water increases with increasing pressure and pressure increases with depth, deep water can 

be hotter than boiling water near the surface. If the pressure that confi nes this deep 

water is reduced quickly, pockets of water 

may suddenly boil, causing an explosion 

as the water is converted to steam. Such 

activity drives the eruptions of geysers, like 

Old Faithful, which are repetitive releases 

of plumes of steam and water. Rarely, 

steam explosions are more violent and can 

hurl water and rock thousands of feet. In 

Yellowstone’s geologic past, such violent 

events, called “hydrothermal explosions,” 

have occurred countless times, creating new 

landscapes of hills and craters.

A recent and notable hydrothermal explosion occurred in 1989 at Porkchop Geyser 

in Norris Geyser Basin. The remains of this 

explosion are still clearly visible today as 

an apron of rock debris 15 feet (5 m) across 

surrounding Porkchop’s central spring. 

In the 1880s and early 1890s, a series of 

powerful hydrothermal explosions and 

geyser eruptions occurred at Excelsior 

Geyser in the Midway Geyser Basin. Some 

of the explosions hurled large rocks as far 

as 50 feet (15 m). 

Much larger hydrothermal explosions 

have occurred at Yellowstone in the recent 

geologic past. More than a dozen large 

hydrothermal-explosion craters formed 

between about 14,000 and 3,000 years ago, 

triggered by sudden changes in pressure of 

the hydrothermal system. Most of these craters are within the Yellowstone Caldera or 

along a north-south-trending zone between 

Norris and Mammoth Hot Springs.

The largest hydrothermal-explosion 

crater documented in the world is along 

the north edge of Yellowstone Lake in an 

embayment known as Mary Bay. This 1.5-

mile (2.6 km)-diameter crater formed about 

13,800 years ago and may have had several 

separate explosions in a short time interval. What specifi cally triggered these very 

large events is not fi rmly established, but 

earthquakes or a pressure release caused by 

melting glaciers or rapid changes in lake 

level may have been a signifi cant factor.

Yellowstone National Park research geologist Rick 

Hutchinson examines rock debris thrown out in a 1989 

hydrothermal explosion at Porkchop Geyser. [In March 

1997, Hutchinson was killed in a snow avalanche while on 

duty inspecting thermal features in the park.] (Photograph 

courtesy of Robert Smith, University of Utah.)

Geysers and hot springs are common expressions of a hydrothermal 

(hot water) system, but sometimes 

changes in “plumbing” result in large 

volumes of water suddenly fl ashing 

into steam, causing violent hydrothermal explosions. A large hydrothermal 

explosion can hurl water and rock 

thousands of feet and create new 

landscapes of hills and craters. In 

Yellowstone’s geologic past, hydrothermal explosions have occurred 

countless times.

In 1881, Colonel Philetus W. Norris, 

Yellowstone National Park’s second 

superintendent, witnessed a spectacular hydrothermal explosion at 

Excelsior Geyser in the Midway Geyser 

Basin. He described the aftermath as 

follows: “The pool was considerably 

enlarged, its immediate borders swept 

entirely clear of all movable rock, 

enough of which had been hurled or 

forced back to form a ridge from knee 

to breast high at a distance of from 20 

to 50 feet [ 6 to 15 m] from the ragged 

edge of the yawning chasm.” After a 

series of such explosions that ended 

in the early 1890s, Excelsior, once the 

world’s largest active geyser, became 

a quietly boiling hot spring. Except for 

several geyser eruptions in 1985, it has 

remained so ever since.

A more recent hydrothermal explosion occurred in 1989 at Porkchop 

Geyser in Norris Geyser Basin. The remains of this explosion are still clearly 

visible today as a 15-foot (5 m)-diameter apron of rock debris surrounding 

Porkchop’s central spring.

Much larger hydrothermal exploExcelsior Geyser 

erupted in a series 

of violent hydrothermal explosions 

in the 1880s and 

early 1890s; one 

of these eruptions 

is shown in this 

colorized postcard 

made from a photograph. These were 

the largest such 

events to occur in 

the Yellowstone 

region in historical 

times. (Original 

photograph by 

F. Jay Haynes, 

1888; date on postcard is incorrect.)

Colonel Philetus W. Norris 

was Yellowstone National 

Park’s second superintendent (1877 to 1882). A 

decorated Civil War Union 

veteran, Norris enjoyed 

challenges, and his efforts 

were essential in putting 

the park’s management 

on a sound footing. (Photograph courtesy of the 

National Park Service.)

sions have occurred at Yellowstone in the recent geologic past. The 

greatest concentration of hydrothermal-explosion craters lies around 

the north end of Yellowstone Lake. These craters owe their origins 

to spectacular explosions thousands of years ago.

HYDROTHERMAL (STEAM) EXPLOSIONS AT YELLOWSTONE
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Eruptions of the Yellowstone volcanic 

system have included the two largest 

volcanic eruptions in North America 

in the past few million years; the third 

largest was at Long Valley in California 

and produced the Bishop ash bed. The 

biggest of the Yellowstone eruptions occurred 2.1 million years ago, depositing 

the Huckleberry Ridge ash bed. These 

eruptions left behind huge volcanic 

depressions called “calderas” and 

spread volcanic ash over large parts 

of North America (see map). If another 

large caldera-forming eruption were to 

occur at Yellowstone, its effects would 

be worldwide. Thick ash deposits would 

bury vast areas of the United States, and 

injection of huge volumes of volcanic 

gases into the atmosphere could drastically affect global climate. Fortunately, 

the Yellowstone volcanic system shows 

no signs that it is headed toward such an 

eruption in the near future. In fact, the 

probability of any such event occurring 

at Yellowstone within the next few thousand years is exceedingly low.

Volcanic ash, like this ash from the 

1980 eruption of Mount St. Helens, is 

made up of tiny jagged particles of 

rock and glass (see inset, magnifi ed 

about 200 times). Even a light dusting 

of volcanic ash can pose a health 

hazard to people and animals and damage crops, electronics, 

and machinery. Heavy ash fall, such as that from a large calderaforming eruption, would devastate the surrounding area and 

affected areas downwind. (USGS photographs.)

Explosive eruptions are best compared by recalculating the volume of erupted volcanic ash and 

pumice (see photos) in terms of the original volume of molten rock (magma) released (shown 

in this diagram by orange spheres). On this basis, the 585 cubic miles (mi 3

) of magma that was 

erupted from Yellowstone 2.1 million years ago (Ma) was nearly 6,000 times greater than the 

volume released in the 1980 eruption of Mount St. Helens, Washington, which killed 57 people 

and caused damage exceeding $1 billion. Even the 1815 Tambora, Indonesia, eruption—the 

largest on Earth in the past two centuries—was more than fi ve times smaller than the smallest 

of Yellowstone’s three great prehistoric eruptions at 1.3 Ma.

Volcanic Ash Fall from Yellowstone Eruptions

PREHISTORIC CALDERA-FORMING ERUPTIONS OF YELLOWSTONE

How Big Were the Yellowstone Eruptions?
Printed on recycled paper 6

Jacob B. Lowenstern, Robert L. Christiansen, 

Robert B. Smith, Lisa A. Morgan, and Henry Heasler

For more information contact:

Yellowstone National Park

http://www.nps.gov/yell/home.htm

or

U.S. Geological Survey

(650) 329-5227

http://volcanoes.usgs.gov/yvo/

See also Tracking Changes in Yellowstone’s Restless 

Volcanic System (USGS Fact Sheet 100-03)

and other USGS volcano Fact Sheets

http://volcanoes.usgs.gov/Products/sproducts.html

This Fact Sheet and any updates to it are available online 

at http://pubs.usgs.gov/fs/2005/3024/

THE YELLOWSTONE VOLCANO 

OBSERVATORY

Increased scientifi c surveillance of 

Yellowstone in the past 30 years has 

detected unmistakable changes in its 

vast underground volcanic system, 

similar to historical changes observed 

at many other large calderas (volcanic depressions) in the world. To 

strengthen the capabilities of scientists 

to track and respond to changes in 

Yellowstone’s activity, a fi fth U.S. 

volcano observatory was created in 

2001, complementing existing ones 

for Hawaii, Alaska, the Cascades, and 

Long Valley, California. The Yellowstone Volcano Observatory (YVO) is 

supported jointly by the U.S. Geological Survey, the University of Utah, and 

Yellowstone National Park.

The principal goals of YVO include:

• Strengthening the monitoring system 

for tracking earthquake activity, uplift 

and subsidence, and changes in the 

hydrothermal (hot water) system;

• Assessing the long-term potential hazards of volcanism, earthquakes, and 

explosive hydrothermal activity in the 

Yellowstone region;

• Enhancing scientifi c understanding 

of active geologic and hydrologic 

processes occurring beneath Yellowstone and in the surrounding region 

of the Earth’s crust; and

• Communicating new scientifi c results, 

the current status of Yellowstone’s 

activity, and forecasts of potential 

hazardous hydrothermal explosions 

or volcanic eruptions to Yellowstone 

National Park staff, the public, and 

local, State, and Federal offi cials. 

Current real-time-monitoring data are 

online at http://volcanoes.usgs.gov/

yvo/monitoring.html .

These very large and violent hydrothermal explosions are independent of associated volcanism. None of the large hydrothermal events of the past 16,000 years has 

been followed by an eruption of magma. 

The deeper magma system appears to be 

unaffected even by spectacular steam explosions and crater excavations within the 

overlying hydrothermal system. 

Although large hydrothermal explosions 

are a feature of Yellowstone’s recent geologic history, most explosions in historical 

times have been relatively small and have 

left craters at most a few yards across. For 

example, in early 2003, a long linear fi ssure 

appeared on a hillside above Nymph Lake, 

north of Norris Geyser Basin, venting 

steam and throwing bits of rock onto the 

surrounding hillside. Although most hydrothermal explosions in the park are small, 

their remains can be noticed by observant 

visitors and attest to the nearly continuous 

geologic activity at Yellowstone. 

How Dangerous Is Yellowstone?

None of the events described above—

cataclysmic caldera-forming eruptions, 

lava fl ows, large earthquakes, or major 

hydrothermal explosions—are common 

in Yellowstone. Although visitors to Yellowstone National Park may never experience them, some hazardous events are 

certain to occur in the future. Fortunately, 

systematic monitoring of Yellowstone’s 

active volcanic and hydrothermal systems, 

including monitoring of earthquakes and 

ground deformation, is now carried out 

routinely by YVO scientists. This monitoring will allow YVO to alert the public 

well in advance of any future volcanic 

eruptions. Currently the ability to reli-

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Scientists evaluate natural-hazard levels by combining their knowledge of the 

frequency and the severity of hazardous events. In the Yellowstone region, 

damaging hydrothermal explosions 

and earthquakes can occur several 

times a century. Lava fl ows and small 

volcanic eruptions occur only 

rarely—none in the past 70,000 years. 

Massive caldera-forming eruptions, 

though the most potentially devastating 

of Yellowstone’s hazards, are extremely 

rare—only three have occurred in the 

past several million years. U.S. Geological Survey, University of Utah, and 

National Park Service scientists with 

the Yellowstone Volcano Observatory 

(YVO) see no evidence that another 

such cataclysmic eruption will occur at 

Yellowstone in the foreseeable future. 

Recurrence intervals of these events 

are neither regular nor predictable.

ably predict large quakes or hydrothermal 

explosions, events more likely than a volcanic eruption, remains a challenge. However, changes in the patterns of ongoing 

seismicity or other indicators of possible 

geologic unrest are quickly reported to offi cials responsible for public safety in the 

National Park Service and other agencies.

Through continuous monitoring and 

research, YVO is greatly improving understanding of Yellowstone’s volcanic, 

earthquake, and hydrothermal hazards. 

The work of USGS scientists with YVO 

is only part of the USGS Volcano Hazards Program’s ongoing efforts to protect 

people’s lives and property in all of the 

volcanic regions of the United States, including California, Hawaii, Alaska, and 

the Pacifi c Northwest.

Edited by Peter H. Stauffer and James W. Hendley II

Graphic design by Susan Mayfi eld and Sara Boore

Banner design by Bobbie Myers

COOPERATING ORGANIZATIONS

 Yellowstone National Park 

University of Utah

Smaller events are more likely

HAZARDOUS EVENTS AT YELLOWSTONE

Catastrophic events are rare