U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2013–3014

 April 2013

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

Mount St. Helens, 1980 to Now—What’s Going On?

Civilization exists by geological consent, 

subject to change without notice. 

 –Will Durant

The spectacular 1980 eruption at 

Mount St. Helens opened a new episode 

in the volcano’s history that began more 

than 250,000 years ago. Fifty-seven 

people lost their lives as a result of the 

eruption, and dramatic changes to the 

landscape occurred and will continue 

long into the future. Lava domes grew 

in the 1980 crater during 1980–86 and 

2004–8. A new glacier— Crater Glacier 

—formed, and streams began eroding 

and transporting millions of tons of sediment downstream. Years later, hot dome 

rocks are still steaming, Crater Glacier 

is still advancing, rock falls send plumes 

of dust skyward, and streams continue to 

erode and transport sediment away from 

the volcano. Meanwhile, magma (molten rock) is accumulating again beneath 

the volcano. Scientists are keeping a 

close watch on Mount St. Helens and 

the other Cascade volcanoes to assess 

hazards and provide timely warnings 

of future activity. Arming yourself with 

knowledge and following a few simple 

recommendations will help you prepare 

for future eruptions. 

Throughout these pages, the camera 

symbol ( ) calls attention to video 

clips of volcanic processes that can be 

accessed from the online version of 

this Fact Sheet (http://pubs.usgs.gov/

fs/2013/3014). For more information 

about volcanoes in the United States and 

around the world, visit the U.S. Geological Survey (USGS) Volcano Hazards 

Program website: http://volcanoes.usgs.

gov/.

1980—Earth’s Inner Fury 

Uncorked 

On May 18, 1980, Mount St. 

Helens in southwest Washington State 

erupted violently, killing 57 people. The 

picturesque conical volcano had been 

rumbling for months, but on that morning its north side collapsed in one of the 

largest debris avalanches (landslides) 

in history, triggering a lateral blast that 

devastated 150 square miles and sent 

up an eruption column that reached 

More is going on than meets the eye in this south-facing photo of Mount St. Helens taken on June 8, 2005. 

An unrelenting flow of semi-solid magma rises from a vent on the crater floor at a rate of about 10 feet per 

day, pushing up skyscraper-size spines. The spines collapse to form a steaming mound of lava called a lava 

dome. Split in two by the growing dome, Crater Glacier has started to flow more quickly northward. When the 

eruption ended in early 2008, the two arms of the glacier had met again after encircling both the new dome 

and an earlier one that grew from 1980 to 1986. Stream channels near the bottom of the photo continued 

to erode, and massive amounts of sediment moved downstream, clogging rivers and increasing the threat 

of floods—processes that will continue far into the future. In the distance are two other Cascade Range 

volcanoes—Oregon’s Mount Hood (left) and Mount Jefferson (center). USGS photo by John Pallister.

Mount St. Helens seized the world’s attention in 

1980 when the largest historical 

landslide on Earth and a powerful 

explosive eruption reshaped the 

volcano, created its distinctive crater, and dramatically modified the 

surrounding landscape. An enormous lava dome grew episodically 

in the crater until 1986, when the 

volcano became relatively quiet. 

A new glacier grew in the crater, 

wrapping around and partly burying 

the lava dome. From 1987 to 2003, 

sporadic earthquake swarms and 

small steam explosions indicated 

that magma (molten rock) was being replenished deep underground. 

In 2004, steam-and-ash explosions 

heralded the start of another eruption. A quieter phase of continuous 

lava extrusion followed and lasted 

until 2008, building a new dome 

and doubling the volume of lava 

on the crater floor. Scientists with 

the U.S. Geological Survey and 

University of Washington’s Pacific 

Northwest Seismograph Network 

maintain constant watch for signs 

of renewed activity at Mount St. 

Helens and other Cascade volcanoes. Now is an ideal time for both 

actual and virtual visitors to Mount 

St. Helens to learn more about dramatic changes taking place on and 

beneath this active volcano.
the stratosphere and blanketed areas hundreds of miles downwind with 

ash. The eruption also initiated lahars (volcanic mudflows) that choked 

nearby rivers. The landslide deposit—its surface strewn with huge blocks 

of shattered rock called hummocks—buried the North Fork of the Toutle 

River valley as much as 600 feet (180 meters) deep for a distance of 13 

miles (21 kilometers). Part of the landslide overtopped a ridge 1,150 

feet (350 meters) high 6 miles (10 kilometers) north of the volcano, 

leaving a deposit called The Run-Up or The Spillover. The eruption 

destroyed nearly all of the volcano’s glaciers, and lahars choked the 

Toutle, Cowlitz, and Columbia River channels with sediment. Pyroclastic flows—ground-hugging avalanches of hot volcanic ash, pumice, rock 

fragments, and gases that destroy everything in their path—rushed out of 

the crater left by the landslide and formed the Pumice Plain in the valley 

below. Five more explosive eruptions during summer 1980 sent columns 

of ash jetting into the stratosphere, disrupting life in the Pacific Northwest and threatening air travel.

From December 1980 to October 1986, a lava dome grew episodically on the crater floor, eventually reaching a height of nearly 1,000 feet 

(305 meters) and a volume of 120 million cubic yards (92 million cubic 

meters). Snowfall and avalanches from the steep crater walls collected 

on the crater floor, where they were shaded from sunlight during most 

of the year. As a result, Crater Glacier formed and began to flow—the 

newest and only expanding glacier in the Cascade Range. Newly formed 

streams began the monumental task of eroding and transporting millions 

of tons of sediment downstream. More than three decades later, only 

about 8 percent of the sediment dumped into the river system in 1980 has 

been eroded away. The downstream flood threat from rivers clogged with 

mobilized sediment will require attention for decades to come.

2004—The Volcano Erupts Again

In September 2004, almost 18 years after the 1980–86 lava dome 

stopped growing, a swarm of shallow earthquakes and a rapidly growing 

welt on the crater floor signaled that Mount St. Helens was about to erupt 

again. Scientists warned that a new eruption could start explosively, and 

on October 1 the first of several explosions shot a plume of volcanic ash 

and gases into the sky. Lava emerged from the top of the welt about 10 

days later. For the next 3+ years, scientists and spectators alike marveled 

as a series of hot, solid, smooth-sided lava “spines” rose from the vent, 

bulldozed their way across the crater floor, and piled up to form a new 

dome 1,500 feet (455 meters) high.

Crater Glacier was split in two by the growing dome and shoved 

against the surrounding crater walls. The glacier responded by flowing 

northward around the east and west sides of the 1980–86 dome at rates 

Mount St. Helens as seen from the north shore of Spirit Lake before the 

May 18, 1980, eruption. USFS photo by Jim Nieland, U.S. Forest Service, 

Mount St. Helens National Volcanic Monument.

Eruption column at Mount St. Helens on May 18, 1980, as seen from the 

west. Prevailing winds carried most of the ash to the east. The resulting 

deposit was more than an inch (2.5 cm) thick in the town of Ritzville, 

Washington, 200 miles downwind. Some of the finest ash reached the 

stratosphere and circumnavigated the globe. A pyroclastic flow can be 

seen descending the volcano’s north flank in the lower left part of the 

photo. USGS photo by Austin Post.

Thick, pasty lava flow emerges onto the surface of the 1980-86 dome 

on June 26, 1981. The 1980-86 dome grew episodically by accumulation 

of more than a dozen flows like this one, plus by internal growth from 

magma that pushed upward but did not reach the surface. USGS photo 

by Dan Dzurisin.

By the Numbers: The 1980 Eruption

1,314 feet (400 meters)—Elevation lost during May 18, 1980, landslide

and eruption—from 9,677 feet (2,950 meters) before to 8,363 feet 

(2,550 meters) after

2,084 feet (635 meters)—Depth of crater formed in 1980

0.60 cubic miles (2.5 cubic kilometers; 3.3 billion cubic yards; 165 million 

large dump trucks)—Volume of May 18, 1980, landslide deposit

80,000 feet (24,000 meters)—Height reached by May 18, 1980 eruption 

column in less than 15 minutes. The ash cloud spread across the 

United States in 3 days and circled Earth in 15 days.

0.26 cubic miles (1.0 cubic kilometers)—Volume of volcanic ash (before compaction by rainfall) erupted on May 18, 1980. Noticeable 

amounts of ash fell in 11 states.

1980–1986
Mount St. Helens is a dynamic landscape that is constantly changing. What kinds of eruption products give the volcano its shape? Which features in this image changed dramatically 

on May 18, 1980, or since? Almost all of the terrain in the foreground and middle ground of this image (the devastated area) was affected by the 1980 blast. Can you name some geologic 

processes that are active now? For help with the answers, check the surrounding photographs and text (answers appear on the last page). This shaded relief image was produced from 

lidar data. Lidar is an acronym for Light Detection and Ranging, a modern remote sensing technique used to map topography more accurately than was possible with older techniques. 

The crater is 1.2 miles (1.9 km) wide east-west. Elsewhere the scale varies owing to the oblique viewing angle.

Steam and ash plume from Mount St. Helens on March 8, 

2005, as seen from the USGS Cascades Volcano Observatory 

in Vancouver, Washington, about 40 miles south-southwest 

of the volcano. USGS photo by Matt Logan.

The U.S. Army Corps of Engineers dredged sediment from 

the Toutle (shown here), Cowlitz, and Columbia Rivers. By 

1987, the volume of material removed was equivalent to a 

highway 12 lanes wide, 1 foot thick, stretching from New 

York to San Francisco. USGS photo by Lyn Topinka, February 

5, 1981.

Steep-walled channel eroded into hummocky 1980 landslide 

deposit along North Fork of Toutle River. Sediment produced 

by rapid cutting down is deposited downstream, increasing 

threat of floods and reducing salmon runs. USGS photo by 

Jon Major.

PRODUCTS AND LEGACY OF MOUNT ST. HELENS’ ERUPTIONS
of several feet per day. In early 2008, the two arms of the glacier met on 

the north side of the dome. By the time the eruption ended in early 2008, 

the new dome had grown to a volume of 124 million cubic yards (95 million cubic meters)—very nearly the same as the 1980–86 dome. Today 

(2013), no new lava is being added to the crater and the rate of advance 

of Crater Glacier has slowed to the pre-2004 value of about 1 foot per 

day (0.3 meters per day).

Dramatic Changes Occur Before Your Eyes and Beneath Your 

Feet

Years after the construction of the lava domes of 1980–86 and 

2004–8, hot dome rocks are still steaming. Crater Glacier is still advancing and surrounds both domes. Rock falls send plumes of dust skyward. 

Sediment is the lasting legacy of past eruptions—erosion of 1980 deposits is creating steep-sided channels in the North Fork of the Toutle River 

valley, and millions of tons of sediment are being carried downstream, 

increasing flood hazards. This material originated from the upper part of 

Mount St. Helens, which slid away on May 18, 1980, and it is now on its 

way to the Columbia River and beyond. 

Beneath the volcano, magma is accumulating again and building for 

another eruption—quite possibly within our lifetimes. Scientists are carefully tracking these and other changes in this most dynamic landscape in 

the Pacific Northwest.

Silent Forces Beneath Us Create Volcanoes of the Cascade 

Range

Slow collisions of Earth’s tectonic plates sustain Cascade volcanoes. Mount St. Helens is the most active volcano in the Cascade volcanic arc, a chain of volcanoes stretching 700 miles (1,100 kilometers) 

from Lassen Peak in northern California to Mount Garibaldi and beyond 

in southern British Columbia, Canada—part of the famous Pacific “Ring 

of Fire.” The Cascadia section of the Ring of Fire exists because, off 

the Pacific Northwest coast, the Juan de Fuca Plate is colliding with 

and sinking beneath the North American Plate at a rate of 1–2 inches 

(3–5 centimeters) per year. Scientists call this type of boundary between 

colliding plates a subduction zone, with one plate subducting (sliding 

beneath) the other. As the plates move, strain builds up in the rocks along 

subduction zones. This strain is sometimes released in great earthquakes, 

such as the 1700 Cascadia earthquake off the Pacific Northwest coast and 

the 2011 Tōhoku earthquake in Japan.

Subduction plays a key role in generating the magmas that 

form and feed Cascade volcanoes. The surprise ingredient in the 

Explosive onset of the 2004-08 dome-building eruption on October 1, 

2004. Light parts of the eruption plume are primarily steam; dark parts 

are laden with ash and ballistic blocks. The southwest rim of the 1980 

crater is on the left. Crater Glacier is between the base of the crater 

wall and the vent. USGS photo by John Pallister.

Helicopter flying past lava spine emerging from vent on crater floor. A 

series of hot, solid lava spines like this one piled up to form the 2004-08 

dome. During an eruption, when semisolid magma scrapes against 

vent walls, it forms a smooth, soft “fault gouge” surface—a texture 

also seen on rocks lining California’s San Andreas fault. USGS photo 

by Dan Dzurisin, April 28, 2006.

Scientist (circled) examining the toe of Crater Glacier, which advanced 

northward across the crater floor as a result of the 2004-08 eruption. 

Rock debris covering the surface of the glacier and incorporated 

within the glacial ice originated mostly from rockfalls off the steep 

crater walls or off one of the two lava domes on the crater floor. USGS 

photo by Dave Ramsey, August 17, 2009.

By the Numbers: Mount St. Helens since 1980

120 million cubic yards (92 million cubic meters; 6.1 million large dump 

trucks)—Volume of 1980–1986 lava dome

124 million cubic yards (95 million cubic meters; 6.3 million large dump 

trucks)—Volume of 2004–2008 lava dome

0.88 cubic yards (0.67 cubic meters) per second—Average lava extrusion 

rate October–December 2006 (Equivalent to filling 25 Olympic 

swimming pools every day)

6 percent—Portion of volume removed on May 18, 1980, that has been 

replaced by growth of two lava domes

5 feet (1.5 meters) per day—Average advance rate of Crater Glacier during 2004–2008 dome building eruption. Before, its advancement was 

about 1 foot (0.3 meters) per day.

8 percent—Portion of 1980 eruptive material eroded and transported 

downstream as valley-filling sediment of 2012

2004–PRESENT
Oceanic Crust Continental Crust

Mantle Mantle

Juan 

de Fuca

Ridge

Cascadia Trench

Sea Level

Sea Level

Mount Rainier

Mount Adams Mount St. Helens

Mount Hood

Glacier Peak

Mount Baker

Mount Garibaldi

Mount Meager

Magma 

accumulation

at base of crust

Region of

magma

formation

Magma conduit

Upper

Mantle

Continental

Crust

Magma–from source to surface

1200o

C 1100o

C 1000o

C

Shallow magma

storage

Zone of water release

1300o

C

Subducting slab

magma-generating process is—water. 

Deep within the Earth, extreme heat 

breaks down water-bearing minerals in 

the sinking Juan de Fuca Plate, releasing 

hot water into the overlying rocks of the 

Earth’s mantle. The added water lowers 

the melting temperature of mantle rock, 

causing some of it to melt. The resulting 

magma is less dense than surrounding 

rock, so it rises into the Earth’s crust, 

where its heat triggers more melting and 

the formation of magma reservoirs. As 

magma approaches Earth’s surface, water 

vapor and other gases in the magma 

expand and provide additional energy for 

a volcanic eruption.

Monitoring Can Provide Advance 

Warning of Future Eruptions

Volcanoes generally don’t produce 

large earthquakes like those that occur 

along plate boundaries, but sometimes 

swarms of hundreds to thousands of 

small quakes occur beneath a volcano 

and provide clues to processes occurring 

deep underground. Ground deformation (swelling, stretching) occurs when 

the pressure beneath a volcano changes, 

which can mean that magma is accumulating or moving toward the surface. A 

change in the amount or composition of 

gases released from magma as it rises 

toward the surface also can foretell an 

impending eruption. By monitoring and 

analyzing earthquakes, ground deformation, and volcanic gas emissions, 

scientists are better able to understand a 

volcano’s behavior, to assess hazards and 

potential impacts, and to provide timely 

warnings of future events.

 Mount St. Helens is a world-class 

natural laboratory where USGS and other 

scientists are learning about processes of 

rapid landscape change, the magma system that feeds the volcano, and the volcanic and tectonic forces that shape the 

Pacific Northwest, as well as the warning 

signs and hazards associated with eruptions. Mount St. Helens is the volcano in 

the Cascades most likely to erupt again 

in our lifetimes. The exact timing and 

magnitude of the next eruption cannot be 

forecast long in advance, but our growing 

knowledge base and continued monitoring will enable the USGS to provide 

short-term forecasts and warnings—as 

was done in 1980 and 2004.

Those who cannot remember the past are 

condemned to repeat it.

 –George Santayana

Be Prepared for Future Eruptions 

Experience has shown that Mount 

St. Helens tends to be relatively quiet 

Block diagram showing subduction of the Juan de Fuca Plate beneath the North American Plate 

along the Cascadia Trench, which is the western edge of the Cascadia subduction zone. Oceanic 

crust forms by eruptions along the Juan de Fuca Ridge. As the Juan de Fuca Plate drifts eastward, 

it cools, becomes more dense, and eventually dives under the less dense North American Plate 

at the Cascadia Trench. Water released from the subducting slab causes the overlying mantle to 

partially melt, 

forming magma 

that sustains the 

Cascade Range 

of volcanoes 

(black triangles). 

USGS graphic by 

Lisa Faust.

Diagrammatic cross section of a subduction 

zone, showing locations of magma formation, 

accumulation, and storage beneath a 

volcano such as Mount St. Helens. Magma 

forms above the subducting slab of oceanic 

crust and accumulates at the base of 

Earth’s rigid crust, then collects in a storage 

zone 5-8 miles beneath the volcano before 

eruption. USGS graphic by Lisa Faust.

U.S. Geological Survey (USGS) scientists are monitoring Mount St. Helens in various ways in order to be able to warn of future eruptions. Left: Examining 

earthquake signals from Mount St. Helens at the Cascades Volcano Observatory in Vancouver, Washington. USGS photo by Carolyn Driedger, March 29, 2012. 

Middle: Setting up Global Positioning System (GPS) equipment to measure ground deformation on the east flank of the volcano. USGS photo by Mike Poland, 

September 29, 2004. Right: Installing volcanic-gas monitoring equipment in a helicopter before a flight over the volcano. Gases are released from magma as it 

moves upward or cools underground. USGS photo by Steve Schilling, September 27, 2004.
Revised March 2013

Kelso

Woodland St. Helens

Ridgefield

Yacolt

Battle Ground

Vader

Toledo

Castle Rock

Toutle

Longview

Silver Lake

Spirit

Lake

Lake 

Merwin

Mount 

St. Helens

Columbia

River

Coweeman River

Lewis River Kalama River

Cowlitz

River

Fork

North

Mount

Adams

Hazard 

Zones Johnston Ridge

Observatory

Regional 

Lava Flow 

Hazard Zone

Cougar Lewis

River Road

Forest Service Road 25

South Fork Toutle River

Kalama Swift 

Reservoir Yale 

Lake

Toutle River

502

503

503

4

504

505

503

5

30

30

5

0 5 10 Kilometers

50 10 Miles

Volcano Hazard Zones

Near–volcano: lava and pyroclastic flows, 

thick tephra, lahars, ballistic ejecta, rock fall

Lahars (volcanic mudflows): potentially 

far-travelled in valleys draining volcano

Regional lava flows: lava flows from small, 

isolated volcanic vents possible

Volcanic ash (not shown): fine fragments 

of volcanic rock carried downwind

VOLCANO HAZARDS IN THE 

MOUNT ST. HELENS REGION

This simplified hazard map shows areas that are 

prone to ground-based hazards from eruptions 

at Mount St. Helens. Mauve color indicates 

areas at risk from lava flows and avalanches 

of hot rock and gases called pyroclastic flows. 

Bright red areas that fade to orange and yellow 

indicate potential routes for lahars (volcanic 

mudflows). Not shown are areas subject to 

hazards from volcanic ash. Volcanic ashfall 

is often a nuisance but can be a more serious 

hazard during large explosive eruptions. Even 

in small concentrations, airborne ash can be a 

serious threat to aircraft (http://pubs.usgs.gov/

fs/2010/3116/). The distribution of ash depends 

upon the speed and direction of winds at the 

time of the eruption. Sand color shows areas at 

risk from possible lava flows from other volcanic 

vents in the area.

between eruptions, with occasional 

earthquake swarms and minor amounts of 

ground movement (deformation) and volcanic gas emission. Scientists continue to 

monitor the volcano closely for any sign 

of a change from the normal background 

level of activity, but until that happens 

the timing of the next eruption cannot be 

known. On the other hand, we know from 

the geologic record at Mount St. Helens 

that additional explosive eruptions are 

possible and that dome building can go 

on episodically for decades to centuries. 

So the dome-growth episodes in 1980–86 

and 2004–08 are probably not the last 

in this series. If past trends are repeated, 

renewed dome growth will be preceded 

by a few days to weeks of heightened 

earthquake activity, ground deformation, 

and gas emission. 

People who are knowledgeable and 

prepared can better survive a volcanic 

eruption. Following the recommendations 

below will help you prepare for, and 

recover from, the next eruption.

The hazard zonation map for Mount 

St. Helens shown above reflects current 

understanding and will be updated as 

conditions warrant. Becoming familiar 

with the hazard map is a good start to 

ensuring your safety in the event of an 

eruption. Stay informed about the status 

of Mount St. Helens and other Cascade 

volcanoes through the news media and 

via the USGS Volcano Hazards Program 

website: http://volcanoes.usgs.gov/.

Daniel Dzurisin, Carolyn L. Driedger, and Lisa M. Faust

Edited by Peter H. Stauffer

Graphic design by Vivian T. Nguyen

Illustrations by Lisa M. Faust

Banner design by Bobbie Myers

COOPERATING ORGANIZATIONS

U.S. Forest Service

For more information contact:

U.S. Geological Survey

David A. Johnston Cascades Volcano Observatory

1300 SE Cardinal Court, Bldg. 10, Suite 100

Vancouver, WA 98683–9589

Tel: (360) 993–8900, Fax: (360) 993–8980

e-mail: cvo@usgs.gov

http://volcanoes.usgs.gov

See also Pre-1980 eruptive history of Mount St. Helens, 

Washington (USGS Fact Sheet 2005–3045) 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

ANSWERS (to questions posed in caption of lidar image)

Eruption products that give the volcano its shape: Lava flows, lava domes, pyroclastic 

flows, lahars, ashfall deposits.

Features that changed dramatically on or since May 18, 1980: Summit area slid away and 

the crater formed (May 18); landslide deposit was emplaced (May 18); pyroclastic flows 

formed the Pumice Plain (May 18); lava domes grew during 1980–86 and 2004–08; streams 

cut deep channels and waterfalls formed; Crater Glacier grew and advanced.

Processes active now: Erosion by water, wind, and ice; rockfalls, mainly from crater 

walls; movement of Crater Glacier; magma accumulation in a reservoir a few miles 

beneath the volcano.

http://pubs.usgs.gov/fs/2013/3014

Learn: Knowledge brings power. Live 

safely and with less disruption by seeking out information 

about how your community is 

at risk. The USGS Cascades 

Volcano Observatory website 

(http://volcanoes.usgs.gov/

observatories/cvo/) is a good 

source for such information.

Inquire: Ask Federal, State, and local 

government agencies about 

community emergency plans and 

preparedness measures that can 

help protect your family.

Prepare: Stockpile supplies and 

develop an emergency communication plan to help your family 

live with greater safety and peace 

of mind.