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May 18, 1980: The eruption of Mount St. Helens

The views expressed are those of the author and are not necessarily those of Scientific American.


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October 1792 the crew of the “H.M.S. Discovery“, surveying the western coasts of the American continent, spotted a mountain and named it after the British diplomat Alleyne FitzHerbert, 1st Baron St. Helens (1753-1839).
The true origin of Mount St. Helens was revealed to the naturalists only in 1835, when a minor eruption revealed its volcanic nature. In November 1842 the missionary Josiah Parrish experienced an ash rain and earthquakes of unknown origin, but generated probably by the active St. Helens. This phase of volcanic activity continued until 1857.

To the local tribe of the Klickitat people the mountain was already known as “Loo-Wit Lat-kla” – “Keeper of the Fire” or “Louwala-Clough” – “One from Whom Smoke Comes” and also  as “Tah-one-lat-clah” – “the Fire- or Smoking-Mountain”. According to their legends, the mountain was once the beautiful princess Loo-Wit, disputed by two warriors in a battle of fire and smoke. To end the battle all three were transformed in mountains: the beautiful and shy princess became the symmetrical, ice covered St. Helens; the two angry warriors became Mount Hood in the south and Mount Adams in the west. This myth was possibly inspired by the observation of a prehistoric eruption of one of the mentioned volcanoes, but there are also direct eyewitnesses’ reports: in 1800 the Sanpoil and Spokan Indians told to the first missionaries and traders visiting the area of an eruption occurring on St. Helens.

The people called it snow… The ashes fell several inches deep all along the Columbia and far on both sides. Everybody was so badly scared that the whole summer was spent in praying. The people even danced – something they never did except in winter.
They didn’t gather any food but what they had to have to live on. That winter many people starved to death.
(Oral traditions originally recorded by anthropologist Verne F. Ray in the late 1920s from the Sanpoil and Nespelem Indians of northeast Washington).

Minor eruptions with small explosions and lava flows occurred again in 1898, 1903 and 1921.
In 1969 geologists Dwigth Crandell warned during a congress in San Francisco that the volcanoes of the U.S. were still poorly studied and monitored and much more active than previously assumed. Based on dated deposits of past eruptions, Crandell published with colleague Donal Mullineaux a paper in which he warned that “the scheme of activity of St. Helens led to the assumption that it is possible to postulate an eruption in the next 100 years and maybe even before the end of this century“.
In March 1980 finally a monitoring system was installed on St. Helens, in response to increased interest of the behaviour of volcanoes located along a subduction zone, as is the Cascade Range, after a surprising and destructive eruption of the Arenal in Central America.
The system registered from the very beginning an increased seismic activity at the mountain. In March 1980 earthquakes with a magnitude of 4 happened periodically and March 27, an explosion occurred – it was now clear that St. Helens had entered a new eruption phase. The volcano became intensively monitored and in April the northern slope started to swell, a phenomena caused by intruding magma inside the mountain. An eruption seemed inevitable and the area around the volcano was closed to the public.

Sunday morning – May 18, at 8:32 – an earthquake of magnitude 5.1 triggered one of the largest landslide-avalanche ever to be recorded (with an estimated volume of 2.8 cubic kilometres) on the northern slope of the mountain, followed by a gigantic explosion. In just 60 seconds the mountain shrinked from 2.950m (9.678 feet)  to 2.549m (8.362 feet), 600 square kilometres of forest were devastated by a 600°C hot pyroclastic flow and the burst of the explosion. The melting glaciers and the overspill of Spirit Lake caused lahars that devastated the valley of the Toutle River.

Fig.1. Mount St. Helens, image in public domain, by the U.S. Geological Survey Photographic Library.

Despite the evacuation, 57 people were killed, many of them scientists studying the active volcano – nobody expected that the eruption would occur so fast and be so furious. David Johnston, U.S.G.S. geologist, was well aware of the possible risk of staying with his observation station close to the mountain, but he remained there right up to the moment of the eruption – his last recorded words and the first mention of the eruption were:

Vancouver, Vancouver, this is it!

It is thanks to his and many others work that the eruption of St. Helens is one of the best documented in history. Two geologists, Dorothy and Keith Stoffel, were overflying St. Helens when it erupted:

The whole north side of the summit crater began to move as one gigantic mass,…[] The entire mass began to ripple and churn without moving laterally. Then the whole north side of the summit began sliding to the north along a deep-seated slide plane.

Also many reporters, hikers and volcano-enthusiast, located outside the danger zone, documented the eruption with photographs or descriptions.

This video, created with photographs taken by Gary Rosenquist, stationed at 18km northeast of St. Helens in the morning of May 18, shows the dynamics of the slope collapse and the pyroclastic explosion. The first photo was taken at 8:27, in the next 6 minutes Rosenquist take a dozen photos before he escaped from the approaching pyroclastic flow. The landslide previous the eruption is well visible as the block moves downward, followed by the pyroclastic flow projecting first upward, then sideward and then surpassing the landslide.

Despite the impacts of the eruption on economy, society and the landscape, the eruption at St. Helens was only a single event in the long history of the Fire-Mountains of the Cascade Range. Like in the fossil forests of Yellowstone, many times the landscape around St. Helens was destroyed, reborn and modified by volcanic eruptions. Today St. Helens is monitored and the area protected to understand the colonization by animals and plants of a devastated volcanic landscape – a new chapter to be written in the geologic record.

Bibliography:

DAVIS, L. (2008): Natural Disasters. Facts on File Science Library. Infobase Publishing: 464
CRANDELL, D. R. & MULLINEAUX D, R., (1978): Potential hazards from future eruptions of Mount St. Helens, Washington: U.S. Geological Survey Bulletin 1383-C: 26
GUNN, A.M. (2008): Encyclopedia of Disasters – Environmental Catastrophes and Human Tragedies. Vol.1. Greenwood Press, London: 733
LEWIS, T.A.(ed) (1985): Volcano (Planet Earth). Time-Life Books: 176

David Bressan About the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts through time. Follow on Twitter @David_Bressan.

The views expressed are those of the author and are not necessarily those of Scientific American.





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