Mount St. Helens National Volcanic Monument

1980 - 2005 Eruption 25th Anniversary

	Mount St. Helens at 25 Reflection and Renewal

Mount St. Helens four months after the May 18, 1980 eruption, as viewed from Johnston Ridge. (Photo by Harry Glicken)

Gas rich magma and super-heated groundwater trapped inside the volcano were suddenly released in a powerful lateral blast. In less than three minutes, 230 square miles of forest lay flattened. The hot gas and magma melted the snow and ice that covered the volcano. The resulting floodwater mixed with the rock and debris to create concrete-like mudflows that scoured river valleys surrounding the mountain.

A plume of volcanic ash and pumice billowed out of the volcano reaching a height of 15 miles and transformed day into night across Eastern Washington. Avalanches of super-heated gas and pumice, called pyroclastic flows, swept down the flanks of the volcano. While the landslide and lateral blast were over within minutes, the eruption column, mudflows and pyroclastic flows continued throughout the day and following night.

By the following morning major eruptive activity had ceased and the landscape appeared to be a gray wasteland.