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U.S. GEOLOGICAL SURVEY—REDUCING THE RISK FROM HAZARDS Living with Volcanic Risk in the

he of the Pacific TNorthwest 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, (1980–86 and 2004–8), and , Cali- fornia (1914–17). To help protect the ’s rapidly expand- ing population, USGS scientists at the Cascades Volcano Observatory in , Washington, monitor and assess the hazards posed by the region’s volcanoes.

On May 18, 1980, after 2 months of and minor eruptions, Mount St. The more than 1 million residents of the -Tacoma, Washing- Helens, Washington, exploded in one of the ton, area live in the shadow of 14,411-foot-high , the most devastating volcanic eruptions of the tallest volcano in the outside of Alaska. Several communities near the volcano, built on the 20th century. Although less than 0.1 cubic deposits of giant of and that are less than 1,200 years old, are at risk from similar future lahars. Inset photograph shows a U.S. Geological Survey (USGS) scientist monitoring the volcano for mile of molten () was erupted, 57 signs of subtle ground movement that might lead to an eruption or . Photos by Lyn Topinka, USGS. people died, and damage exceeded $1 billion. Fortunately, most people in the area were able (pyroclastic flows), flows, and eruptions deposited volcanic ash at least as far to evacuate safely before the eruption because can devastate areas 10 or more miles away; away as . public officials had been alerted to the danger and huge of volcanic ash and debris, Mount Rainier has produced at least ten by U.S. Geological Survey (USGS) and called lahars, can inundate valleys more than 50 eruptions and numerous lahars in the past 4,000 other scientists. As early as 1975, USGS miles downstream. Falling ash from explosive years. It is capped by more glacier ice than researchers had warned that Mount St. Helens eruptions can disrupt activities hundreds the rest of the Cascade volcanoes combined, might soon erupt. Coming more than 60 of miles downwind, and drifting clouds of fine and parts of Rainier’s steep slopes have years after the last eruption in the Cascades ash can cause severe damage to jet aircraft even been weakened by hot, acidic volcanic gases (Lassen Peak), the explosion of St. Helens thousands of miles away. and water. These factors make this volcano was a spectacular reminder that the millions Because the population of the Pacific especially prone to landslides and lahars. of residents of the Pacific Northwest share the Northwest is rapidly expanding, the volcanoes Mount St. Helens is the most frequently region with live volcanoes. of the Cascade Range in Washington, , active volcano in the Cascades. During the past and northern are some of the most 4,000 years, it has produced many lahars and a Volcanoes of the Cascades dangerous in the United States. wide variety of eruptive activity, from relatively The volcanoes of the Cascade Range, quiet outflows of lava to explosive eruptions which stretches from into Washington much larger than that of May 18, 1980. , have produced more than erupted in the mid-1800s has produced few eruptions 100 eruptions, most of them explosive, in for the first time in several thousand years. during the past several thousand years. This just the past few thousand years. However, Activity at steam vents () in Sherman volcano’s most recent activity was a series of individual Cascade volcanoes can lie dormant Crater, near the volcano’s summit, increased small eruptions about 1,000 years ago. for many centuries between eruptions, and in 1975 and is still vigorous, but there is no the great risk posed by volcanic activity in the evidence that an eruption is imminent. Oregon region is therefore not always apparent. has erupted at least six last erupted about 200 years When Cascade volcanoes do erupt, times in the past 4,000 years. About 13,000 ago, producing pyroclastic flows, lahars, and high-speed avalanches of hot ash and rock years ago, an especially powerful series of a prominent (Crater Rock) near the

U.S. Department of the Interior USGS Fact Sheet 165–97 U.S. Geological Survey Revised March 2008 ERUPTIONS OF THE PAST 4,000 YEARS Of the 13 po- volcano’s summit. Most recently, a series of Mount Baker steam blasts occurred between 1856 and 1865. tentially active volcanoes in the Glacier Peak last erupted more than Cascade Range Mount Rainier

20,000 years ago. However, eruptions nearby of the Pacific WASH n Mount St. Helens Northwest, 11 have produced several lava flows and small a have erupted in e Mount Adams volcanic cones in the past 10,000 years. the past 4,000 c O Mount Hood

Three Sisters Volcanic Center in central years. More than c i Mount Jefferson 100 eruptions, f Oregon includes five large volcanoes—North i most of which c Sister, Middle Sister, South Sister, , a OREG were explosive, P and . About 2,000 years ago, have occurred eruptions occurred on South Sister, as well as during that pe- riod, making the from several small volcanoes north of North volcanoes of the Sister. Since 1997, a broad area centered 3 Cascade Range some of the most Lassen Peak miles west of South Sister has domed upward CALIF hazardous in the 4,000 2,000 0 200 by more than 8 inches. Scientists think that United States. YEARS AGO this doming reflects the ongoing accumulation Each eruption of magma at a depth of 3 to 4 miles. The symbol in the diagram represents from one to several eruptions closely spaced in time at or near the named volcano. Eruptions have also occurred from other vents (not shown) scattered throughout the Cascade Range, outcome of this activity is uncertain, but there especially in central Oregon and southwestern Washington. is no evidence that an eruption is imminent. The USGS and its partners have increased , lahars, and ash that fell as far scientists also have conducted many new monitoring efforts in the area to detect any away as Elko, Nevada, 300 miles to the east. studies of the past geologic behavior of Cascade changes that might warrant more concern. volcanoes. These studies allow assessments Newberry Volcano, a broad shield Reducing the Risk of long-term hazards (including lahars and covering more than 500 square miles, is After the 1980 eruption of Mount St. landslides, which can occur even when a capped by Newberry Crater, a large volcanic Helens, Congress provided increased funding volcano is not erupting) and provide the data for depression () 5 miles across. Its most that enabled the USGS to establish a volcano hazard-zone maps that enable communities to recent eruption was about 1,300 years ago. observatory for the Cascade Range. Located in make wise land-use-planning decisions and to Crater Lake occupies a 6-mile-wide Vancouver, Washington, the David A. Johnston prepare emergency-response plans. caldera formed 7,700 years ago when the Cascades Volcano Observatory (CVO) was The work of CVO scientists is helping summit of an ancient volcano (referred to named for a USGS scientist killed at a forward residents of the Pacific Northwest live with as ) collapsed during a huge observation post by the May 18, 1980, eruption. volcanic risk and plan for volcano emergencies. . More than 10 cubic miles Scientists at CVO quickly recognized that it This work is only part of the USGS Volcano of magma was erupted, 10 times as much as was not economically feasible to fully monitor Hazards Program’s ongoing efforts to protect in any other eruption in the Cascades during all potentially active Cascade volcanoes. To people’s lives and property in all of the the past 10,000 years. Smaller eruptions address this and similar problems elsewhere volcanic regions of the United States, including ending about 5,000 years ago formed Wizard in the United States and abroad, the USGS the Pacific Northwest, eastern California, Island and several submerged cones and lava developed a suite of portable volcano- Wyoming, Alaska, and Hawaii. domes on the lake floor. monitoring instruments—essentially, a portable Dan Dzurisin, Peter H. Stauffer, and volcano observatory. In the Pacific Northwest, James W. Hendley II Northern California when regional networks of sensors, Graphic design by Sara Boore, Bobbie Myers, and Susan Mayfield Medicine Lake Volcano, a broad shield operated in cooperation with the University COOPERATING ORGANIZATIONS capped by a 4- by 7-mile-wide caldera, has of Washington’s Pacific Northwest Seismic Federal Aviation Administration erupted at least seven times in the past 4,000 Network, detect unusual seismic activity at a National Oceanic and Atmospheric Administration National Park Service years, most recently about 950 years ago. With volcano, CVO staff will rapidly deploy this State geological surveys and emergency-management agencies of a volume of more than 130 cubic miles, it is the portable equipment to evaluate the hazard and, Washington, Oregon, and California University of Washington largest volcano in the Cascades. if needed, provide timely warnings to local U.S. Forest Service Mount Shasta has been the most active officials and the public. For more information contact: volcano in California during the past 4,000 CVO also uses remote sensing as an U.S. Geological Survey years. During that time, Shasta has erupted on early-detection tool. A technique called David A. Johnston Cascades Volcano Observatory 1300 SE Cardinal Court, Building 10, Suite 100, average about once every 300 years, producing interferometric synthetic-aperture radar Vancouver, WA 98683 many pyroclastic flows and lahars. It probably (InSAR) allows scientists to measure subtle Tel: (360) 993-8900, Fax: (360) 993-8980 e-mail: [email protected] last erupted in 1786. movements of the ground surface, using radar URL: http://vulcan.wr.usgs.gov/ or Lassen Volcanic Field, including Lassen images obtained by Earth-orbiting satellites. USGS Volcano Hazards Program http://volcanoes.usgs.gov/ Peak, is the southernmost volcanic center The current ground doming at Three Sisters This Fact Sheet and any updates to it are available online at: in the Cascades. The most recent volcanic was first detected using this technique. http://pubs.usgs.gov/fs/1997/fs165-97/ eruptions in California occurred at Lassen CVO was able to issue accurate warnings of See also What Are Volcano Hazards? (USGS Fact Sheet 002–97), Peak from 1914 to 1917. An explosive the small eruptions that occurred in 1980–86 Mobile Response Team Saves Lives in Volcano Crises (USGS eruption on May 22, 1915, produced a large and in 2004 at Mount St. Helens. Observatory Fact Sheet 064–97)

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