Living with Volcanic Risk in the Cascades
Fact Sheets (.pdf)
- Cascades Volcanic Risk Fact Sheet
- Volcano Fact Sheet
- Mt. Rainier
- Mt. Baker
- Mt. Hood
- Cascade erruptions during the last 4000 years
Related Links
- The Pacific Northwest Seismic Network
- Lahar Exercise Orting
- Mt. Rainier Lahar Flow
- Pierce County Evacuation Route
- USGS Cascade Range Current Update
- The Pacific Northwest Seismic Network
- WA Emergency Management Division (EMD)
- EMD Preparedness Information
- Cascade Range Volcano Webcams
U.S. Geological Survey—Reducing The Risk From Volcano Hazards
(extracted from Living with Volcanic Risk in the Cascades)
Living with Volcanic Risk in the Cascades
The Cascade Range of the Pacific Northwest has more than a dozen potentially active volcanoes. Cascade
volcanoes tend to erupt explosively, and on average two eruptions occur per century—the most recent were at
Mount St. Helens, Washington (1980–86), and Lassen Peak, California (1914–17). To help protect the Pacific
Northwest’s rapidly expanding population, USGS scientists at the Cascades Volcano Observatory in Vancouver,
Washington, monitor and assess the hazards posed by the region’s volcanoes.
On May 18, 1980, after 2 months of earthquakes and minor eruptions, Mount St. Helens, Washington, exploded
in one of the most devastating volcanic eruptions of the 20th century. Although less than 0.1 cubic mile of molten
rock (magma) was erupted, 57 people died, and damage exceeded $1 billion. Fortunately, most people in the area
were able to evacuate safely before the eruption because public officials had been alerted to the danger by U.S.
Geological Survey (USGS) and other scientists. As early as 1975, USGS researchers had warned that Mount St.
Helens might soon erupt. Coming more than 60 years after the last eruption in the Cascades (Lassen Peak), the
explosion of St. Helens was a spectacular reminder that the millions of residents of the Pacific Northwest share
the region with live volcanoes.
Volcanoes of the Cascades
The volcanoes of the Cascade Range, which stretches from northern California into British Columbia, have produced
more than 100 eruptions, most of them explosive, in just the past few thousand years. However, individual Cascade
volcanoes can lie dormant for many centuries between 
eruptions, and the great risk posed by volcanic activity in
the region is therefore not always apparent.
When Cascade volcanoes do erupt, high-speed avalanches of hot ash and rock (pyroplastic flows), lava flows, and landslides can devastate areas 10 or more miles away; and huge mudflows of volcanic ash and debris, called lahars, can inundate valleys more than 50 miles downstream. Falling ash from explosive eruptions can disrupt human activities hundreds of miles downwind, and drifting clouds of fine ash can cause severe damage to jet aircraft even thousands of miles away.
Because the population of the Pacific Northwest is rapidly expanding, the volcanoes of the Cascade Range in
Washington, Oregon, and northern California are some of the most dangerous in the United States.
Of the 13 potentially active volcanoes in the Cascade Range of the Pacific Northwest, 11 have erupted in the past 4,000 years, and 7 in just the past 200 years. More than 100 eruptions, most of which were explosive, have occurred in the past 4,000 years, making the volcanoes of the Cascade Range some of the most hazardous in the United States. Each eruption symbol in the diagram represents from one to several dozen eruptions closely spaced in time. Eruptions have also occurred from other vents (not shown) scattered throughout the Cascade Range, especially in central Oregon and southwestern Washington.
Dan Dzurisin, Peter H. Stauffer, and James W. Hendley II
Tel: (360) 993–8900, Fax: (360) 993–8980
http://vulcan.wr.usgs.gov/
or
USGS Volcano Hazards Program
http://volcanoes.usgs.gov
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