1980 eruption of Mount St. Helens
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On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive eruption took place on May 18, 1980, at 8:32 am. The eruption, which had a volcanic explosivity index of 5, was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California. It has often been declared the most disastrous volcanic eruption in U.S. history.
Photograph of the eruption column, May 18, 1980, taken by Austin Post
Mount St. Helens from Monitor Ridge, this image shows the cone of devastation, the huge crater open to the north, the posteruption lava dome inside, and Crater Glacier surrounding the lava dome. The small photo on the left was taken from Spirit Lake before the eruption and the small photo on the right was taken after the eruption from roughly the same place. Spirit Lake can also be seen in the larger image, as well as Mount Rainier and Mount Adams.
USGS photo showing a pre-avalanche eruption on April 10
Photo showing the bulge growing due to a cryptodome on April 27
Pyroclastic flow
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A pyroclastic flow is a fast-moving current of hot gas and volcanic matter that flows along the ground away from a volcano at average speeds of 100 km/h but is capable of reaching speeds up to 700 km/h. The gases and tephra can reach temperatures of about 1,000 °C (1,800 °F).
Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984
Pyroclastic rocks from the Bishop tuff; uncompressed with pumice (on left), compressed with fiamme (on right)
Building remnant in Francisco Leon destroyed by pyroclastic surges and flows during eruption of El Chichon volcano in Mexico in 1982. Reinforcement rods in the concrete were bent in the direction of the flow.
A scientist examines pumice blocks at the edge of a pyroclastic flow deposit from Mount St. Helens