What Happened When Mt. St. Helens Erupted?


Quick Answer

When Mt. St. Helens erupted on May 18, 1980, the blast devastated 229 square miles (596 meters) and destroyed millions of dollars worth of timber. During the eruption, the lateral blast removed the upper 1,306 feet (396 meters) of the “Bulge” on the north face of the volcano.

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Full Answer

After the side of the mountain had been removed, an explosion of volcanic gases produced a lateral blast that traveled at speeds of up to 670 miles per hour. It overtook the landslide, extending up to 19 miles, destroying trees, houses and wildlife in its path and leaving the area as barren as the landscape on the moon.

The blast toppled trees closest to the volcano and up to 8 miles away, leaving them lying in neat rows. Trees farther away remained standing, but hot gases singed them to brown skeletons. Fifty-seven people were killed, most by asphyxiation, including the volcanologist David Johnston, when the lateral blast scorched their lungs.

In March of 1980, Mt. St. Helens started reawakening after being inactive since the mid 19th century. In that same month, scientists actively began monitoring the volcano when a 4.2 magnitude earthquake caused it to start venting steam. The historic eruption is the largest recorded in history; superheated rock fragments and gases exploded in a lateral instead of a vertical direction, something that no one had witnessed before in modern times.

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