Washington is home to five major composite volcanoes or stratovolcanoes (from north to south): Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams. These volcanoes and Mount Hood to the south in Oregon are part of the Cascade Range, a volcanic arc that stretches from southwestern British Columbia to northern California.
Although there are thousands of small basaltic or basaltic-andesitic volcanoes in the Cascade Range, the 13 major composite volcanic centers in the U.S., all part of the range, have been the focus of most hazards concerns. During the past 12,000 years, these volcanoes have produced more than 200 eruptions that have generated tephra (ejected material), lava flows, and lahars (volcanic debris flows) and debris avalanches. It is important to note that other enormous debris avalanches and lahars may have been caused by intrusions of magma (not eruptions) or steam explosions at the volcanoes or by local or regional earthquakes because these flowage events do not correlate with known tephra layers.
All Washington volcanoes except Mount Adams have erupted within the last 250 years (see table below). However, the volcanoes do not erupt at regular intervals, thus making it difficult to forecast when a given volcano might come to life again. Although worldwide the risks from volcanoes are significantly lower than risks from earthquakes and landslides, the relatively long recurrence interval for volcanic hazards (decades to several centuries) combined with their great potential for destruction make them particularly insidious.
Mount Baker | ash, lava | 1? | mid-1800s; 1870?; 1975 steam emission | debris avalanches and lahars have flowed down the Nooksack, Baker, and Skagit Rivers |
Glacier Peak | ash | 1+? | before 1800 | lahars have extended more than 60 mi (100 km) down the Skagit River; pyroclastic flows produced several times |
Mount Rainier | ash, lava | 1? | X tephra between 1820-1854 | enormous debris avalanches and lahars flowed down the White, Puyallup, and Nisqually Rivers; smaller lahars in the Cowlitz basin; continued seismic activity |
Mount St. Helens | ash, lava, dome | 2 major eruptive periods | 1980-present | history of explosive eruptions and lahars |
Indian Heaven volcanic field | lava, scoria | none | 8,000 yr ago? | consists of seven minor shield volcanoes that have each erupted only once (?) |
Mount Adams | lava, ash | none | 3,500 yr ago | lahars |
Mount Hood, Oregon | ash, dome | 2+? | 1865; major eruption in the late 1700s | lahars down the Sandy and Hood Rivers; modern glacial outburst floods; seismic swarms continue |
Above text modified from: Pringle, Patrick T., 1994, Volcanic hazards in Washington—A growth management perspective: Washington Geology, v. 22, no. 2, p. 25-33.
Online Field Trip Guide:
Cascades Volcanoes--Processes and Hazards: A Five Day Field Trip, Mount Baker to Mount St. Helens [PDF; 10.3 MB]
- by Patrick T. Pringle (formerly of the Washington Division of Geology and Earth Resources, now at Centralia Community College) and Catherine J. Hickson (Geological Survey of Canada). This guide was written for a field trip held September 25-30, 1998, in conjunction with the 8th Congress of the International Association of Engineering Geology and the Environment, Vancouver, B.C., September 21-25, 1998
Online Publications
Report of Investigations 24: Mount St. Helens Ash—Properties and Possible Uses, by W. S. Moen and G. B. McLucas. 1981. 60 p. [PDF; 14 MB]
Postglacial Influence of Volcanism on the Landscape and Environmental History of the Puget Lowland, Washington: A Review of Geologic Literature and Recent Discoveries, with Emphasis on the Landscape Disturbances Associated with Lahars, Lahar Runouts, and Associated Flooding [external PDF; 591 KB]
- from Puget Sound Research 2001, the fifth Puget Sound Research Conference, February 12-14, 2001
- by Patrick Pringle (formerly of the Washington Division of Geology and Earth Resources, now at Centralia Community College) and Kevin Scott (U.S. Geological Survey, Cascades Volcano Observatory)