Volcanoes of the Cascadia Subduction Zone


August 17 (WEDNESDAY!!), 6 p.m., Teton Co. Library Auditorium – Open to Public. Presentation: ” MOUNT ST. HELENS AND OTHER VOLCANOES OF THE CASCADIA SUBDUCTION ZONE”. Presented by Bob Tilling, Volcanologist Emeritus, Volcano Science Center, U.S. Geological Survey.

Before 1980, few people outside of Washington State were aware of the existence of Mount St. Helens, let alone its potential for wreaking death and destruction.  That suddenly changed early morning of 18 May 1980, when this volcano—dormant since 1857—exploded violently following two months of intense earthquake activity and intermittent, weak activity.  This cataclysmic eruption produced the worst volcanic disaster in the recorded history of the United States, causing well over $1 billion in economic losses, disrupting the lives of thousands for weeks to years, and leaving behind 57 fatalities.  Predictably, the 1980 eruption abruptly and dramatically increased governmental and public awareness that volcanic eruptions can also happen in the conterminous (“Lower 48”) part of the United States—not only in Hawaii and Alaska.  Equally important, it was realized that Mount St. Helens is but one of many potentially active volcanoes in the Cascade Range of the Pacific Northwest, any one of which could possibly reactivate in the future.  This realization spurred the establishment in 1980 of a permanent USGS facility—the Cascades Volcano Observatory—to systematically monitor the then-continuing activity at Mount St. Helens and also to initiate monitoring of other Cascade volcanoes.

In his presentation, Bob Tilling will first review the 1980 Mount St. Helens eruption, its impacts, and subsequent eruptive activity.  He will then focus on the plate-tectonics setting and processes of the ”Cascadia Subduction Zone” that created the entire ”Cascades Volcanic Arc” (CVA), which stretches for ~1,250 km from southern British Columbia to northern California.  Together, the CVA and the Aleutian Volcanic Arc comprise the North American segment of the notorious circum-Pacific ”Ring of Fire,” which hosts more than 75% of the world’s active and potentially active volcanoes.  Like the major Cascade volcanoes, most volcanoes of this ”Ring” are stratovolcanoes (or composite volcanoes) that are driven by subduction processes and typically erupt explosively.  While even the largest eruptions of stratovolcanoes are smaller than some from the so-called ”supervolcanoes” (e.g., Yellowstone), they occur much, much more frequently.  Not surprisingly, explosive eruptions from Earth’s subduction-zone volcanoes have been the most destructive and deadly since the dawn of civilization, killing more than 300,000 people since 1600 A.D.  Being ready for the next catastrophic eruption—whenever and whereever it might strike—poses a formidable challenge for scientists and emergency-management officials, despite advances in volcano monitoring and forecasting capability.