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This Day in History, 1980: Mount St. Helens Erupts

(Today's historical post is dedicated to scarlettina.)

Twenty-five years ago today, on May 18, 1980:

At 8:32 a.m. PDT, Mount St. Helens, a volcanic peak in southwestern Washington, suffered a massive eruption, killing 57 people and devastating some 210 square miles of wilderness.

Called Louwala-Clough, or "the Smoking Mountain," by Native Americans, Mount St. Helens is located in the Cascade Range and stood 9,680 feet before its eruption. The volcano has erupted periodically during the last 4,500 years, and the last active period was between 1831 and 1857. On March 20, 1980, noticeable volcanic activity began again with a series of earth tremors centered on the ground just beneath the north flank of the mountain. These earthquakes escalated, and on March 27 a minor eruption occurred, and Mount St. Helens began emitting steam and ash through its crater and vents.

Small eruptions continued daily, and in April people familiar with the mountain noticed changes to the structure of its north face. A scientific study confirmed that a bulge more than a mile in diameter was moving upward and outward over the high north slope by as much as six feet per day. The bulge was caused by an intrusion of magma below the surface, and authorities began evacuating hundreds of people from the sparsely settled area near the mountain. A few people refused to leave.

On the morning of May 18, Mount St. Helens was shaken by an earthquake of about 5.0 Richter magnitude, and the entire north side of the summit began to slide down the mountain. The giant landslide of rock and ice, one of the largest recorded in history, was followed and overtaken by an enormous explosion of steam and volcanic gases, which surged northward along the ground at high speed. The lateral blast stripped trees from most hill slopes within six miles of the volcano and leveled nearly all vegetation for as far as 12 miles away. Approximately 10 million trees were felled by the blast.

The landslide debris, liquefied by the violent explosion, surged down the mountain at speeds in excess of 100 miles per hour. The avalanche flooded Spirit Lake and roared down the valley of the Toutle River for a distance of 13 miles, burying the river to an average depth of 150 feet. Mudflows, pyroclastic flows, and floods added to the destruction, destroying roads, bridges, parks, and thousands more acres of forest. Simultaneous with the avalanche, a vertical eruption of gas and ash formed a mushrooming column over the volcano more than 12 miles high. Ash from the eruption fell on Northwest cities and towns like snow and drifted around the globe within two weeks. Fifty-seven people, thousands of animals, and millions of fish were killed by the eruption of Mount St. Helens.

By late in the afternoon of May 18, the eruption subsided, and by early the next day it had essentially ceased. Mount St. Helens' volcanic cone was completely blasted away and replaced by a horseshoe-shaped crater-the mountain lost 1,700 feet from the eruption. The volcano produced five smaller explosive eruptions during the summer and fall of 1980 and remains active today. In 1982, Congress made Mount St. Helens a protected research area.

Personal note: Even thought I was only ten years old at the time, and living in New York City, I remember this event vividly. The news media covered the mini-eruptions with great enthusiasm, and every day we waited anxiously to find out if the volcano had finally erupted.

As often, today's post was taken from http://www.historychannel.com/tdih/tdih.jsp?month=10272957&day=10272983&cat=10272946

Also see http://en.wikipedia.org/wiki/1980_Mount_St._Helens_eruption for even more detail.


From what I recall reading, if the wind had been going a different direction, Portland (50 miles away) would've been a major disaster area with large loss of life from secondary effects of the ash and its accompanying logistics problems. From a bit on what did happen;

The ash fall, however, did pose some temporary major problems for transportation operations and for sewage-disposal and water-treatment systems. Because visibility was greatly decreased during the ash fall, many highways and roads were closed to traffic, some only for a few hours, but others for weeks. Interstate 90 from Seattle to Spokane, Washington, was closed for a week. Air transportation was disrupted for a few days to 2 weeks as several airports in eastern Washington shut down due to ash accumulation and attendant poor visibility. Over a thousand commercial flights were cancelled following airport closures.

The fine-grained, gritty ash caused substantial problems for internal-combustion engines and other mechanical and electrical equipment. The ash contaminated oil systems, clogged air filters, and scratched moving surfaces. Fine ash caused short circuits in electrical transformers, which in turn caused power blackouts. The sewage-disposal systems of several municipalities that received about half an inch or more of ash, such as Moses Lake and Yakima, Washington, were plagued by ash clogging and damage to pumps, filters, and other equipment. Fortunately, as these same cities used deep wells and closed storage, their water-supply systems were only minimally affected.

The removal and disposal of ash from highways, roads, buildings, and airport runways were monumental tasks for some eastern Washington communities. State and Federal agencies estimated that over 2.4 million cubic yards of ash-equivalent to about 900,000 tons in weight-were removed from highways and airports in Washington State. Ash removal cost $2.2 million and took 10 weeks in Yakima.

Now, imagine that sort of thing happening in a large city. Water supply? Getting food in when engines are damaged just by travelling in the area? Etc.

December 2016

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