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TITLE: Water In, Water Out

[Photo: Mount St. Helens Erupts]
The warnings began in March — small earthquakes, mild eruptions, and the ominous bulging of the volcano's north flank. The climax came on May 18: a huge avalanche followed by a 9-hour eruption that served as a sobering reminder of the power of plate tectonics.

8:32 a.m., May 18, 1980: A magnitude-5 earthquake triggered the collapse of Mount St. Helens's summit and north flank — leading to one of the largest debris avalanches in recorded history and a major explosive eruption.

Splintered tree

Only a scrap of bark remains at the base of this splintered tree trunk. The rest was stripped off by the volcano's lateral blast. It felled trees like matchsticks and devastated an area extending to 25-30 km (15-18 mi).

  [Photo: Splintered Tree]

Breadcrust block

This dacite block tumbled from the growing lava dome in Mount St. Helens's crater. After the crust hardened, gas continued to expand in the partly molten interior, swelling and cracking its surface like bread when it bakes.

  [Photo: Breadcrust Block]

Nearby Pumice, Far-flung Ash

During an explosive eruption, large particles fall near the volcano. Finer ash can drift great distances before it settles like snow.

  [Photo: Pumice and Ash]

Nearby Pumice

Immediately after the May 18, 1980, eruption, a hail storm of coarse pumice and rock fragments fell from the eruption cloud, blanketing the area near the volcano. This map shows how much pumice accumulated during the May 18, 1980, eruption of Mount St. Helens.

  [Graphic: Pumice Accumulation]

Far-flung Ash

[Photo: Ash]

Just three hours after the eruption began, fine ash started to fall on Spokane, Washington, 390 km (240 mi) northeast of the volcano. In this electron microscope photo, the fine ash that fell in Spokane, Washington, is magnified 650 times. A dusting of ash was noticed as far as 1,500 km (930 mi) to the east.

  [Graphic: Ash Cloud Movement]

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits