Mount St. Helens

Volcanic Hazards at Mount St. Helens

Mount St. Helen’s high frequency of eruptions during the recent geologic past and its two eruptive episodes of the past three decades indicate a high probability of renewed eruptive activity.

Mount St. Helens simplified hazards map showing potential impact area for ground-based hazards during a volcanic eve

Mount St. Helens, Washington simplified hazards map showing potential impact area for ground-based hazards during a volcanic event. Mauve indicates areas at risk from lava flows and avalanches of hot rock and gases call pyroclastic flows. Bright red areas that fads to orange and yellow indicate potential routes for lahars (volcanic mudflows)? Not shown are areas subject to hazards from volcanic ash.  Volcanic ashfall is often a nuisance but can be a more serious hazard during large explosive eruptions.

(Public domain.)

In addition, the volcano has produced four large explosive eruptions during the past five centuries that affected the Pacific Northwest region and sent large amounts of volcanic ash downwind. Owing to these factors, USGS maintains a robust monitoring program at the volcano to detect signs of renewed unrest and works with Federal, State, and local agencies to develop crisis plans and risk-mitigation strategies. Businesses and citizens should be aware of potential future hazards and consult with local emergency-management agencies for advice on how to prepare for volcano and other types of natural hazards.

Among the possibilities for renewed activity at Mount St. Helens are resumption of lava-dome growth, eruption of basaltic or andesitic tephra and lava flows, explosive eruptions of dacitic tephra and pyroclastic flows, and large lahars that sweep down valleys heading on the volcano.