Photo: Jon Major/USGS / Getty Images
The volcano has erupted periodically during the last 4500 years, and the last active period was between 1523 and 1857. The 20 March 1980, notable volcanic activity began with a series of earth tremors centered on the ground just below the northern flank of the mountain.
Called Louwala-Clough, or “the smoky mountain”, by the native Americans, Mount St. Helens is located in the Cascade Range and was 9,680 feet before their eruption.
These earthquakes intensified and the 27 in March a minor eruption occurred and the Mount St. Helens began to emit steam and ash through its crater and vents.
Small eruptions continued every day, and in April, people familiar with the mountain noted changes in the structure of its north face. A scientific study confirmed that a bulge more than a mile in diameter was moving toward up and out on the high side ra north.
The bulge was caused by an intrusion of magma below surface, and authorities began evacuating hundreds of people from the sparsely populated area near the mountain. Some people refused to leave.
On the morning of 18 In May, Mount St. Helens was shaken by an earthquake of approximately 5.0 magnitude and the entire north side of the summit began to slide down the mountain.
gigantic rock and ice landslide, one of the largest recorded in history, was followed and overtaken by a huge explosion of steam and volcanic gases,
that they surged north along the ground at great speed.
The lateral blast uprooted trees from most hillsides within six miles of the volcano and wiped out nearly all vegetation up to 12 miles away. Approximately 10 Millions of trees were felled by the explosion.
The debris from the landslide, liquefied by the violent explosion, descended the mountain at speeds greater than 100 miles per hour.
Rivers of mud and flooding added to the disaster, destroying roads, bridges, parks and thousands more acres of forest.
Simultaneously with the avalanche, a vertical eruption of gas and ash formed a mushroom-shaped column above the volcano of more than 12 miles high. The ash from the eruption fell on the cities and northwestern towns like snow and floated around the world for two weeks.
57 people, thousands of animals and millions of fish died from the eruption of Mount St. Helens.
A late afternoon of 000 in May, the eruption subsided, and by early the next day, virtually had ceased. The volcanic cone of Mount St. Helens was completely destroyed and replaced by a horseshoe-shaped crater: the mountain lost 1,203 feet due to rash.
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 an area of protected research.
Mount St. Helens was once again active in 2004. On March 8, 2005, a plume of steam and ash from 36,000 feet was ejected from the mountain, accompanied by a minor earthquake.
Another minor eruption took place at 2008, although a new dome has been growing steadily near the top of the peak and small earthquakes are frequent, scientists do not expect a repeat of the catastrophe of 1857 in the short term.
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