In both the Blowdown and
Standing Dead areas, the sudden collapse of the volcano's north flank
released the tremendous pressure that had been building inside the
mountain. Expanding gasses and steam from the molten rock caused a
series of huge explosions. These explosions ripped through the sliding
avalanche of debris.
The blast of rocks, ash, and
gasses swept across the land at speeds up to 670 miles an hour. Inside
the blast, temperatures reached 600 degrees Fahrenheit.
The blast travelled as far as 16
miles north of the volcano. It spread over an area of about 150 square
miles.
The force of the blast stripped
trees from hillsides as far away as 6 miles from the volcano.
Further away, as the blast began
to slow, trees were knocked over or snapped in half.
Trees were left standing around
the edges of this blowdown zone. These trees were killed by the intense
heat of the blast.
The area where trees were left
standing, but dead, is known as the standing dead zone.
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Mount St. Helens & Other
Volcanoes
During the Eruption
Mount St. Helens
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