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Home / Science / Mount St Helens: How the volcano shook itself after the earthquake | Science | news

Mount St Helens: How the volcano shook itself after the earthquake | Science | news



On May 18, 1980, Mount St. Helens broke out in Washington state. The event, which measured in the Volcanic Explosively Index 5, has been described as the most catastrophic in modern US history. A huge column of volcanic material rose 80,000 feet into the atmosphere and dumped ashes in 11 states, killing at least 57 people and causing more than 770 million pounds of damage.

The volcano, an active stratovolcano, had not done so since becoming a threat in the forties and fifties.

However, Amazon Prime's "The Fire Below Us" documentary revealed how a series of small earthquakes indicated that Magma had moved down again.

The following was unveiled in the 1

995 series: "The siren song of Mount St Helens began on March 20.

"He shook himself off in a 4.1 magnitude earthquake.

" For the next 29 days, the mountain continued to tremble with hundreds of trembling.

"The frequency peaked on March 25 with 22 significant earthquakes over a period of eight hours.

"In response to the growing threat, the forestry service began evacuating personnel and set up the first restricted zones, warning residents of the dangers of earthquake-related avalanches."

The Documentary It then became known how the earthquakes became more frequent and a second crater was opened.

It added: "On March 27, a burst of steam and ash opened a new crater on the top of the mountain and Washington's backyard volcano made its new debut.

"A few days later, a second, larger crater formed next to the first one.

"Then the terrible discovery – the north side of St. Helens – had deformed and created a 200-foot-high bulge that was growing at an incredible speed of five feet a day. "

Only two months later, on May 18, a significant activity occurred.

At 8:32 am, a 5.1 magnitude earthquake was centered directly below the north slope trigger. The landslide, the largest in history, moved 110 to 155 miles an hour across the west arm of Spirit Lake.

The landslide exposed the magma of Dacit in St. Helens & # 39; s neck to much lower pressure, causing the gas filled, partially molten rock and high pressure steam above it to break out for a few seconds after the landslide began.

The resulting explosion led the pyroclastic flow of very hot volcanic gases, ash and pumice, formed from new lava laterally, while the powdered old rock enclosed the ground, crossed the moving avalanche and spread outward, leaving a total of about 240 square miles of forest were devastated.

The huge ash cloud sent to the sky from the northern foot of St. Helens was visible in the surrounding areas.

The lateral overburden explosion, laden with volcanic debris, caused devastation up to 30 km from the volcano.


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