24 April 2015 - Mount St. HELENS

Mount St. HELENS

G'day folks,

The eruption of Mt. St. Helens in 1980 was the worst volcanic disaster in U.S. history; however, it offered scientists an exceptional opportunity to examine and study a large volcanic eruption, which has enriched scientific knowledge of volcanoes.

 Overview of Mt. St. Helens:

Mt. St. Helens is a composite volcano within the Cascade Range in what is now southern Washington, approximately 50 miles northwest of Portland, Oregon. Though Mt. St. Helens is approximately 40,000-years old, it is considered a relatively young, active volcano. 

 Mt. St. Helens historically has had four extended periods of volcanic activity (each lasting hundreds of years), interspersed with dormant periods (often lasting thousands of years). The volcano is currently in one of its active periods.

Native Americans living in the area have long known that this was not an ordinary mountain, but one that had fiery potential. Even the name, "Louwala-Clough," a Native American name for the volcano, means "smoking mountain." 

The volcano was first discovered by Europeans when British Commander George Vancouver of the H.M.S.Discovery spotted Mt. St. Helens from the deck of his ship while he was exploring the northern Pacific Coast from 1792 to 1794. Commander Vancouver named the mountain after his fellow countryman, Alleyne Fitzherbert, the Baron St. Helens, who was serving as the British ambassador to Spain.

Piecing together eyewitness descriptions and geologic evidence, it is believed that Mt. St. Helens erupted somewhere between 1600 and 1700, again in 1800, and then quite frequently during the 26-year span of 1831 to 1857. After 1857, the volcano grew quiet. Most people who viewed the 9,677-foot tall mountain during the 20th century, saw a picturesque backdrop rather than a potentially deadly volcano. Thus, not fearing an eruption, many people built houses around the base of the volcano.

On March 20, 1980, a 4.1 magnitude earthquake struck underneath Mt. St. Helens. This was the first warning sign that the volcano had reawakened. Scientists flocked to the area. On March 27, a small explosion blew a 250-foot hole in the mountain and released a plume of ash. This caused fears of injuries from rockslides so the entire area was evacuated. Similar eruptions to the one on March 27 continued for the next month. Though some pressure was being released, large amounts were still building.

 In April, a large bulge was noticed on the north face of the volcano. The bulge grew quickly, pushing outward about five feet a day. Though the bulge had reached a mile in length by the end of April, the plentiful plumes of smoke and seismic activity had begun to dissipate. Thus, as April drew to a close, officials were finding it increasingly difficult to maintain the evacuation orders and road closures due to pressures from homeowners and the media as well as from stretched budget issues.

At 8:32 a.m. on May 18, 1980, a 5.1 magnitude earthquake struck under Mt. St. Helens. Within ten seconds, the bulge and surrounding area fell away in a gigantic, rock avalanche. The avalanche created a gap in the mountain, allowing the release of pent-up pressure that erupted laterally in a huge blast of pumice and ash. The noise from the blast was heard as far away as Montana and California; however, those close to Mt. St. Helens reported hearing nothing. 

The avalanche, huge to begin with, quickly grew in size as it crashed down the mountain, traveling around 70 to 150 miles per hour and destroying everything in its path. The blast of pumice and ash traveled northward at 300 miles per hour and was a raging hot 660° F (350° C). The blast killed everything in a 200-square mile area. Within ten minutes, the plume of ash had reached 10 miles high. The eruption lasted nine hours. 

 For the scientists and others who were caught in the area, there was no way to outrun either the avalanche or the blast. Fifty-seven people were killed. It is estimated that about 7,000 large animals such as deer, elk, and bears were killed and thousands, if not hundreds of thousands, of small animals died from the volcanic eruption. 

Mt. St. Helens had been surrounded by a lush forest of coniferous trees and numerous clear lakes before the blast. The eruption felled entire forests, leaving only burned tree trunks all flattened in the same direction. The amount of timber destroyed was enough to build about 300,000 two-bedroom homes. A river of mud traveled down the mountain, caused by melted snow and released groundwater, destroying approximately 200 houses, clogging up shipping channels in the Columbia River, and contaminating the beautiful lakes and creeks in the area. 

Mt. St. Helens is now only 8,363-feet tall, 1,314-feet shorter than it was before the explosion. Though this explosion was devastating, it will certainly not be the last eruption from this very active volcano.

Clancy's comment: Amazing, eh? And, humans still want to mess with nature, rather than learn to live with it in harmony.

I'm ...


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