Mt. St. Helens is part of the Cascades mountain range in the United States. Cascades mountain range settles on a destructive margin. Juan De Fuca plate (oceanic crust) moved towards the North American Plate (Continental Crust) and formed Cascades mountain range.
Over 120years, Juan De Fuca plate had moved towards the North American Plate bit by bit and had pressured it. The pressure had been released in the year of 1980 and marked magnitude 5 on the Richter scale. By the earthquake, the magma rises to the surface of the earth and causes an eruption.
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