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.
mid-1800s; 1870?; 1975 steam emission
debris avalanches and lahars have flowed down the Nooksack, Baker, and Skagit Rivers
lahars have extended more than 60 mi (100 km) down the Skagit River; pyroclastic flows produced several times
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
history of explosive eruptions and lahars
8,000 yr ago?
consists of seven minor shield volcanoes that have each erupted only once (?)
3,500 yr ago
Mount Hood, Oregon
1865; major eruption in the
lahars down the Sandy and Hood Rivers; modern glacial outburst floods; seismic swarms continue
Above text modified from: Pringle, P. T., 1994, Volcanic hazards in Washington—A growth management perspective: Washington Geology, v. 22, no. 2, p. 25-33.
Loss Estimation Pilot Project for Lahar Hazards from Mount Rainier, Washington, by Recep Cakir and Timothy J. Walsh. Washington Division of Geology and Earth Resources Information Circular 113, 2012, 17 p. [PDF, 2.74 MB]
Roadside Geology of Mount Rainier National Park and Vicinity, by Patrick T. Pringle (formerly of the Division of Geology and Earth Resources, now at Centralia Community College). Washington Division of Geology and Earth Resources Information Circular 107, 2008, 190 p. [PDF, 308 MB complete file or smaller sections for faster download]
Roadside Geology of Mount St. Helens National Volcanic Monument and Vicinity [PDF, 56.7 MB], by Patrick T. Pringle. Washington Division of Geology and Earth Resources Information Circular 88, rev. ed. 2002, 122 p. Also available in two parts for faster download: Part 1 [PDF, 28.0 MB] and Part 2 [PDF, 28.6 MB].
Cascades Volcanoes—Processes and Hazards: A Five Day Field Trip, Mount Baker to Mount St. Helens, by Patrick T. Pringle and Catherine J. Hickson (Geological Survey of Canada). International Association for Engineering Geology and the Environment, 8th Congress, Technical Tour Guide Book Trip 14, 1998, 22 p. [PDF, 10.3 MB]
Volcanic Hazards in Washington—A Growth Management Perspective, by Patrick T. Pringle. Washington Geology, 1994,
v. 22, no. 2, p. 25-33. [PDF, 14.4 MB]
Mount Rainier Volcano Evacuation Plans, by Pierce County Emergency Management. Washington Geology, 2001, v. 29, no. 1/2, p. 38. [PDF, 7.5 MB]
Holocene Glacier Peak Lahar in the Lower Skagit River Valley, Washington, by Joe D. Dragovich, Donald T. McKay, Jr., David P. Dethier, and James E. Beget. Washington Geology, 2000, v. 28, no. 1/2, p. 19. [PDF, 6.8 MB]
Geologic Map Delineates Volcanic Hazards, by Joe D. Dragovich and David K. Norman. In Thomas, William A., 2004, Meeting Challenges with Geologic Maps: American Geological Institute, p. 48-49.
Abstracts on the Geology of Mount Rainier, by various authors. Washington Geology, 2000, v. 28, no. 1/2, p. 24-29. [PDF, 6.8 MB]
Extent and Geometry of the Mid-Holocene Osceola Muflow in the Puget Lowland—Implications for Holocene Sedimentation and Paleogeography, by Joe D. Dragovich, Patrick T. Pringle, and Timothy J. Walsh. Washington Geology, 1994, v. 22, no. 3,
p. 3-26. [PDF, 12.5 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, by Patrick T. Pringle and Kevin M. Scott (U.S. Geological Survey, Cascades Volcano Observatory). In Puget Sound Research 2001, Proceedings: Washington State Puget Sound Water Quality Action Team, 2001, 23 p. [PDF, 591 KB]