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On May 18, 1980, Mount St. Helens erupted in the US state of Washington. The event, which measured 5 on the explosive volcanic index, was declared the most disastrous in modern American history. A huge column of volcanic material has risen in the atmosphere and has left ashes in 11 states, killing at least 57 people and causing more than 770 million pounds of damage.
The volcano, which is an active stratovolcano, was no longer a threat since its last period of activity in the forties and fifties.
However, it was revealed in Amazon Prime's "The Fire Below Us" documentary that a series of small earthquakes indicated that the magma had begun to move back below.
The 1995 series revealed: "The siren song on Mount St Helens began on March 20th.
"He woke up with a magnitude 4.1 earthquake.
"For the next 29 days, the mountain continued to tremble with hundreds of tremors.
"The frequency peaked on March 25 with 22 major earthquakes over an eight-hour period.
"In response to the growing threat, the Forest Service has begun evacuating personnel, establishing the first closed areas and warning people of the dangers of avalanches caused by the earthquake."
The documentary then revealed how earthquakes were becoming more frequent and had opened a second crater.
On March 27, an eruption of steam and ash opened a new crater on top of a mountain and the Washington volcano made its entry into the news.
"A few days later, a second larger crater was formed next to the first one.
"Then, the terrible discovery: the north side of St Helens was deformed, creating a bulge more than 100 meters high that grew at an incredible speed of five feet per day."
It was only two months later, on May 18th, that a significant activity occurred.
At 0832, a magnitude 5.1 earthquake, centered directly under the northern slope, caused this portion of the volcano to slide about seven seconds after the impact.
The landslide, the largest in history, reached speeds of 110 to 155 mph and crossed the western arm of Spirit Lake.
The landslide exposed the dacite the magma in the neck of St. Helens at a much lower pressure, causing the bursting of the partially molten rock loaded with gas and high pressure steam over it a few seconds after the start of the slip ground.
The resultant explosion laterally directed the pyroclastic flow of very hot volcanic gases, ash and pumice formed from new lava, while the old sprayed rock wedged the ground, initially moving at 220 mph but accelerating quickly to 670 mph.
The pyroclastic materials passed through the moving avalanche and spread outward, devastating about 240 square miles of forest.
The huge cloud of ash that followed, sent from the sky to the north foot of St. Helens, was visible in all the surrounding areas.
The almost supersonic lateral explosion, laden with volcanic debris, devastated up to 19 miles from the volcano.
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