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e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, October, 2010

May 18, 1980, the day Mount St. Helens exploded: an amazing

story of destruction and recovery process of the environment

Arun KumarArun KumarArun KumarArun Kumar

“At exactly 8:33:00.5 a.m. on May 18, 1980, the north face of

Mount St. Helens fell away.” (Corcoran, 2005). This sentence

indicates as if some one was monitoring the time when this

volcano will erupt. Well, it was being monitored by David

Johnston, a geologist from the United States Geological Survey

(USGS), who sacrificed his life for the sake of enriching human

knowledge on volcanoes. David and 56 others perished under a

massive avalanche caused by an earthquake shortly after 8.32

a.m. (Corcoran, 2005). The Johnston Ridge Observatory near

this volcano is named after him. The enhanced intensity and

frequency of harmonic tremors around a volcano gives a clear

signal that it is going to erupt.

Mount St. Helens is located on the southern part of the Washington State in the USA. It is a

stratovolcano formed by several layers of ash, pumice and lava ejected by this volcano throughout its

history. This was a symmetrical volcano before May 18, 1980 (Figure 1) but became asymmetrical after

violent eruptions and massive land slide of the north flank (Figure 2). The current statistical details on its

morphology and subsequent changes during various volcanic activities are shown in Figure 3 and Table-

1.

May 18, 1980 Eruption of Mount St. Helens

On March 20, 1980 a 4.1 M earthquake shook Mount St. Helens, and a week later on March 27 a

column of steam and ash rose from its ice covered summit to a height of 7,000 feet with a loud bang.

The eruption and avalanches continued for days and a second crater appeared on the north flank that

later enlarged and merged with the original crater. By April 22 ash and steam eruptions had generally

stopped but harmonic tremors indicating the movement of the molten rock under the volcano continued.

The sound of cracking ground on the north flank was heard due to a “bulge” that was gradually forming.

By the end of April, 1980, this “bulge” grew to 1.25 mile long, 1.0 mile wide and 400 feet high, and it

was growing at the rate of around 5 feet per day. Thus, the north flank became more unstable by May 12

and a 5.0 M earthquake triggered a rock and ice avalanche that ran up to half a mile down. On May 18,

by 7.00 a.m. Mr. Johnston, who was located at the observation point Coldwater II, six miles northwest

of Mount St. Helens’ peak, had taken several measurements on the growing “bulge”. At about 8.32 a.m.

two geologists were flying over the volcano when a 5.1 M earthquake shook that created the massive

land slide. The already unstable north flank suddenly broke loose and skid downhill as a massive rock

avalanche. Ash rich eruption plumes rose from mid slope and from the summit crater. The two flying

geologists witnessed the erupted mass of hot gas, rock, ash and ice and safely landed but Mr. Johnston

could not escape incoming avalanche and perished under it. The following are some facts about this

eruption as described in Corcoran, 2005 and Volcano Review of April, 2007.


Figure 1: Mount St. Helens before May 18, 1980 from Spirit Lake on the north side. United States Forest Service

Photograph by Jim Nieland.

(http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH80_st_helens_spirit_lake_before_may_18_1980_med.jpg)

Figure 2: Mount St. Helens in June, 2010. Northern flank was removed on May 18, 1980. The author with his granddaughter

Shreya in the foreground.

1. In less than 10 minutes, the eruption leveled 230 squire miles of forest.

2. The mountain lost 1300 feet height and 0.67 3

miles of rock volume.

3. The area of new crater became 1.2 x 2.4 miles and 2,000 feet deep.

4. The eruption began with massive landslide (debris avalanche) that buried 14 miles of river valley

to an average depth of 150 feet.

5. The landslide released trapped magma and gas, producing a sideways explosion (lateral blast) of

hot rock and ash killing trees up to 17 miles north of the volcano.

6. Cement-like slurries of glacial melt water and boulders called lahars scoured and buried streams

draining the volcano.


7. A vertical ash eruption rose to a height of 15 miles above the crater and continued for nine hours.

Ash drifted to the east and northeast and traveled at least 950 miles.

8. Fiery avalanches of pumice and hot gases (pyroclastic flows) flowed into the valley north of the

crater.

9. 235 squire miles of land north of this volcano was devastated by hot volcanic debris.

10. Many miles of roads and number of bridges were destroyed.

11. A total of 57 people including the USGS geologist Mr. David Johnston died along with countless

numbers of wild animals.

Since May, 1980 the following volcanic activities and eruptions were recorded from Mount St.

Helens (modified from Volcano Review; April, 2007).

1980-1986: Episodic extrusions of lava built a large dome with in the crater.

September 23 - October 5, 2004: Large numbers of earthquakes occurred and after 18 years of quiet

period this volcano erupts once again. Steam and ash exploded and lava extrudes from crater floor at the

rate of one dump truck load per second and builds a new lava dome.

October 6, 2004 – March 31, 2005: Lava dome growth continues (half of a dump truck load per

second), small steam and dust eruptions.

October, 2006: Seven massive lava spines have been extruded (114 million cubic yards). At nearly

1400 feet, the top of the new lava dome is taller than the Empire State Building of New York (Figure 3).

May, 2007: Lava extrusion decreases (a small pickup truck load every two seconds). No explosive

eruption in a year. Dome rock falls and produced some small ash plumes.

Figure 3: Topographic profiles along a N-S axis through Mount St. Helens' crater. Profiles show geometry of new lava

dome relative to south crater rim, 1980 crater floor, 1980-1986 lava dome, and 2000 glacier surface. USGS Fact Sheet 2005-

3036; April, 2005. (http://pubs.usgs.gov/fs/2005/3036/fs2005-3036.html)

Origin of Mount St. Helens, the Cascade Range and the Pacific Ring of Fire

Mount St. Helens is one of several volcanoes of the Cascade Mountain Range. This range lies

100-150 miles east from the Pacific coast (Figure 4) and stretches for over 700 miles from Lassen Peak

in northern California and runs through Oregon and Washington in the USA and further north to the

Fraser River in southern British Columbia in Canada. Eruption history of the Cascade Range volcanoes

during past 4,000 years is given in figure 4 which shows that Mount St Helens has been the most active


volcano of this range. The volcanoes of the Cascades are called the High Cascades often standing twice

the height of the nearby mountains. Cascade Mountains began to rise seven million years ago in the

Pliocene. The Columbia River Gorge breaks this mountain range. This gorge was formed due to down

cutting of the rising mountain by the Columbia River. This is 4,000 Feet deep, is located along the

Washington-Oregon border and exposes uplifted and warped layers of basalt from the Columbia River

Basalt Plateau. Because of the range's proximity to the Pacific Ocean substantial amount of rain falls on

the western slopes than eastern side.

Figure 4: The volcanoes of the Cascade range and their eruption history for the past 4 K yr. St. Helens has been the most

active volcano of this region. (http://en.wikipedia.org/wiki/File:Cascade_eruptions_in_the_last_4000_years.png)

Figure 5: Distribution of tectonic plates on Earth. These plates are of different sizes and shapes. Red arrows indicate their

relative movement. Note the location of a small Juan de Fuca plate off west coast of North America.

(http://en.wikipedia.org/wiki/Pacific_Ring_of_Fire)


The origin of Mount St. Helens, like other volcanoes of the Cascade Range is related to the

constant movement of several large and small tectonic plates that cover the Earth (Figure 5) and the

geodynamic processes that control the movement of these plates is known among geologists as “Plate

Tectonics”. These are lithospheric plates (the outer layer of the earth) and ride on the asthenosphere.

There are three types of plate boundaries defined by their motion in relation to each other. First the

“divergent boundary”, where plates are moving away from each other like the boundary between the

North American Plate and the Eurasian Plate making the Mid Atlantic Ridge. Second the “convergent

boundary”, where two plates are moving towards each other and one subducts under the other forming

mountain ranges and volcanic arcs, for example, the boundary between the Indian plate and the Eurasian

plate where Indian plate has subducted under the Eurasian plate forming the Himalayan Mountain

ranges. Third the “transform boundary” when two plates move laterally against each other like San

Andreas fault of California (Figure 5). Earthquakes, volcanic activity, mountain-building, and oceanic

trenches form along the plate boundaries. The lateral relative movement of the plates varies typically

ranging from no movement to 100 mm annually. These plates move because the Earth's lithosphere has

lower density than the underlying asthenosphere and are driven by the motion of hot material in the

mantle and lateral density variations that result in convection.

Figure 6: Detailed structure and movement along the

eastern and western boundary of the Juan de Fuca Plate.

The cross section along the points A and B shows how

this plate is subducting under the North American Plate

which melts and forms magma that erupts as volcanoes

and this movement is also responsible for the formation

of Casacade Range.

(http://en.wikipedia.org/wiki/File:Cascade_Range_related

_plate_tectonics-en.svg)

Figure 7: Plate tectonic relationship showing relative

movement of the Pacific Plate, Juan de Fuca Plate resulting in

generation of Earthquakes and volcanoes of the Cascadia

Range.

(http://en.wikipedia.org/wiki/File:Cascadia_earthquake_source

s.png)


Juan de Fuca is a small plate on the western margin of the North American continent (Figure 5,

6). On its eastern margin it is subducting under the North American Plate (Cascadia Subduction Zone)

causing the rise of the Cascade Mountain ranges, responsible for all its volcanic activities and

earthquakes in the region (Figures 4, 7). The western margin of the plate is a faulted divergent boundary

(Juan de Fuca Spreading Zone) forming a spreading center. Thus it is pushing westward in the Pacific

Plate and subducting eastward under the North American Plate (Figures 6, 7).

The Cascadia Range is part of the ‘Pacific Ring of Fire’. It is a series of geotectonic features like

mountains, valleys, volcanoes, oceanic trenches and volcanic arcs that encircles the Pacific Ocean

(Figure 8). In the scientific literature this feature is also known as ‘circum-Pacific seismic belt’, is

around 40,000 km long and has over 452 (over 75 % of all volcanoes) active or dormant volcanoes of

the Earth. The regions covered by the ‘Pacific Ring of Fire’ are seismically very active where about 80

% of world’s largest earthquakes occur.

Figure 8: The “Ring of Fire” showing the location of Mount St. Helens and several trenches.

(http://en.wikipedia.org/wiki/File:Pacific_Ring_of_Fire.svg)

Figure 9: Hazards associated with stratovolcano eruptions. Not all hazards shown will accompany a single eruption,

although a single eruption can produce more than one type of hazard at the same time.

(http://gsc.nrcan.gc.ca/volcanoes/images/fig32_e.jpg)


Environmental Destruction and Recovery

Figure 9 shows the types of hazards a volcanic eruption poses to the environment, although a

single event might not cause all the hazards shown in the figure but in most cases few such hazards can

result from a single eruption. The May 18, 1980 eruption destroyed over 200 2 miles of forest in a 180

0

north of the volcano. Prior to the May 18, 1980 catastrophic event this area was thickly forested by

hemlock, and evergreen trees like Pacific silver fir, Douglas fir and many more species of plants (Figure

1). In these forests lived black-tailed deer, and Roosevelt elk, mountain goats and black bears. A lot of

species of small animals, bees and birds also inhabited these forests. Streams and rives of the area had

abundant ocean-migrating salmon and resident trout, likewise lakes and ponds too were teaming with

diverse forms of life including fishes and frogs. The May 18 event destroyed almost all of this, although

the degree of destruction varied depending on the distance from the volcano and direction of the

movement of pyroclastic flow, north-facing orientation, remaining snow pack, and sheltering ridges and

hills. Figure 10 show the logs of dead trees some of which have been cut probably for local use only.

Figure 10: Massive loss or forests after May 18, 1980

eruption of Mount St. Helens. Several dead trees have been

cut. Photograph by Paresh Maisuraia.

Figure 11: Massive loss or forests after May 18,1980

eruption of Mount St. Helens. See dead trees all over the

hills. This image shows regeneration of new trees in the area.

Photograph by Paresh Maisuria.

After the devastation, it took few months for some forms of life to come back and initiate the

process of re-colonization of the region. As rainfall and melting snow and ice removed ash and pumice

exposing the rich pre-eruption soil, the process of plant re-growth began. Ferns, berries and flowers were

observed in the shelter of dead trees. Even the decaying carcasses of animals were supporting plant life.

The miraculous tenacity of life is exemplified by a bacterium called Archaean bacteria initially reported

from the deep volcanic vents on the sea floor of the Pacific Ocean, was observed in the steam vents and

thermal springs near the lava dome at Mount St. Helens. It is an extreme example of life that

successfully survives high pressures, boiling temperatures and anoxic environments.

As the time goes on lakes and streams have become clear enough to support fish, plants are

growing in most places and gradually transforming grey landscape to green (Figure 11). Since grasses

and other plants are re-colonizing, gradually animals too are coming back because food is available for


them. By this time most of animals native to this region are back and life is thriving once again though

no where close to the pre- 1980 eruption environment.

Table 1: Statistical summary of the volcano, lava dome and the glacier dimension 1980-2005 USGS

Fact Sheet 2005-3036; April, 2005. (http://pubs.usgs.gov/fs/2005/3036/fs2005-3036.html)

Summary of volcano, lava dome, and glacier dimensions 1980-2005

Volcano

Elevation of summit 9,677 feet before 1980; 8,363 after; 1,314 feet

removed

Volume removed by May 18, 1980, eruption 0.67 cubic miles (3.7 billion cubic yards)

Crater dimensions 1.2 miles (east-west); 1.8 miles (north-south);

2, 084 feet deep

Crater floor elevation 6,279 feet

Crater glacier area (September 2000) 0.4 square miles

Crater glacier ice volume (September 2000) 105 million cubic yards

Maximum glacier thickness (September 2000) 650 feet

1980-1986 Lava Dome

Elevation of top of dome 7,155 feet

Height 876 feet above 1980 crater floor

Diameter About 3,500 feet

Volume 97 million cubic yards

2004-2005 Lava Dome (as of February 1, 2005)

Elevation of top of dome 7,642 feet

Height 1,363 feet above 1980 crater floor; 700 feet

above 2000 glacier surface

Dimensions of "whaleback" About 1,550 feet long, 500 feet wide

Diameter of lava dome and welt deformed by magma

intrusion, excluding deformed east glacier arm

About 1,700 feet

Volume of lava dome and welt defomred by magma

intrusion, including deformed east glacier arm

50 million cubic yards

Approximate percentage of crater glacier ice

removed

5% to 10%

Acknowledgements: I thank my son Anshuman and his wife Smita of Ottawa and daughter Anita and her husband Paresh of

Seattle for taking me to British Columbia (Canada), Washington and Oregon (USA). This region probably is the most

beautiful part of the Earth. In June, 2010 we visited national parks, beaches, volcanoes, and water falls and hiked through

lovely temperate rain forests. My baby grand daughter Shreya made this trip especially memorable.

Suggested Readings:

General information written in this article was taken from the following publications.

Corcoran, T. 2005. Mount St. Helens: The Story behind the scenery. K C Publications, Inc.

Volcano Review, April 2007. A publication of the Northwest Interpretive Association in cooperation with the USDA Forest

service. About the Author

Dr. Arun Kumar is a Research Scientist and Professor at the Center for Petroleum and Minerals, Research Institute, King

Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. He obtained his Ph.D. (Stratigraphic Palynology)

from Michigan State University, USA and a second Ph.D. (Environmental Micropalaeontology) from Carleton University,

Canada. Dr. Kumar taught geology at Kumaun University, Nainital, India, University of the West Indies, Kingston,

Jamaica, Carleton University and Concordia University (Montreal) in Canada. He also worked as a geologist and


palynologist with Oil and Natural Gas Corporation of India and Core Laboratories International (USA) in Singapore and

Jakarta, Indonesia. His new research interest is in natural hazards and environmental issues.

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