U.S. GEOLOGICAL SURVEY—REDUCING THE RISK FROM VOLCANO HAZARDS The California Volcano Observatory—Monitoring the State’s Restless Volcanoes Medicine olcanic eruptions happen in Mount Shasta Lake Volcano Vthe State of California about as frequently as the largest earthquakes Lassen Volcanic Center on the San Andreas Fault Zone. At Redding least 10 eruptions have taken place in California in the past 1,000 years—most recently at Lassen Peak in Lassen Volcanic National Park (1914 to 1917) in the northern part of the State—and As a part of the U.S. Geological future volcanic eruptions are inevitable. Survey’s Volcano Hazards The U.S. Geological Survey California Clear Lake Sacramento Program, the California Volcano Volcanic Field Long Valley Observatory aims to advance Volcano Observatory monitors the Volcanic Region scientific understanding of State’s potentially hazardous volcanoes. San Francisco volcanic processes and lessen Ubehebe the harmful impacts of volcanic CALIFORNIA Craters activity in the volcanically active USGS areas of California. More than 50 volcanoes in the CALIFORNIA Fresno United States have erupted one or VOLCANO more times in the past 200 years. The OBSERVATION most volcanically active regions are in Coso Volcanic Field Hawaii, Alaska, Washington, Oregon, EXPLANATION and California. California’s volcanoes Volcano—By threat rank are dispersed throughout the State—from High to very high near its northern border with Oregon Moderate to its southern border with Mexico. Volcano that erupted within the The U.S. Geological Survey California last 3,000 years Los Angeles Volcano Observatory (USGS CalVO) in 0 25 50 MILES Salton Buttes Menlo Park watches over California’s 0 25 50 KILOMETERS potentially hazardous volcanoes to help Base from 2012 U.S. Geological Survey 100-meter digital data communities prepare for, and respond to, Volcanoes of very high to low threat are San Diego volcanic activity. scattered throughout California, from the Oregon border (north) to Mexico (south). Other older volcanoes in California are of less concern. California’s volcano watch list is subject to change as new data on past eruptive activity Some California Volcanoes are are collected, as volcanic unrest changes, and as populations in threatened areas grow or More Hazardous Than Others decline. The half red/half yellow triangle for the Long Valley Volcanic Region denotes that it The USGS has ranked the volcanic is composed of four volcanic centers ranging from moderate to very high threat. threat at all U.S. volcanoes using volcano California Volcanoes Erupt in age, types of potential hazards, and This type of low-level volcanic Various Styles and Produce estimates of the societal exposure to unrest can persist for decades or even Diverse Hazards those hazards. Sixteen volcanoes are hundreds of years without an eruption. on California’s watch list to monitor. Although steady, low-level unrest is Explosive eruptions blast lava Research suggests that partially molten normal for many young volcanoes, fragments (tephra) and gas into the air rock (magma) lies beneath seven of these rapidly accelerating unrest is cause for with tremendous force. The fi nest particles volcanoes—Medicine Lake Volcano, concern. At California’s most threatening (ash) billow upward, forming an eruption Mount Shasta, Lassen Volcanic Center, volcanoes, monitoring sensors are in column that can attain stratospheric Clear Lake Volcanic Field, the Long place to continuously track levels of heights in minutes. Simultaneously, Valley Volcanic Region, Coso Volcanic unrest. Such monitoring is necessary to searing volcanic gas laden with ash and Field, and Salton Buttes. At these determine the baseline, or background coarse chunks of lava may sweep down volcanoes, earthquakes (seismicity), hot level, of activity at a volcano to help the fl anks of the volcano as a pyroclastic springs, volcanic gas emissions, and (or) volcanologists know what is normal. fl o w . Ash in the eruption cloud, carried ground movement (deformation) attest to An uptick in unrest may be a sign of by the prevailing winds, is an aviation their restless nature. increased volcanic threat. hazard and may remain suspended for U.S. Department of the Interior Fact Sheet 2014–3120 U.S. Geological Survey ver. 1.1, June 2019 hundreds of miles before settling to the ground as ash fall. During less energetic effusive eruptions, hot, fl uid lava may issue from the volcano as lava fl ows that can cover many miles in a single day. Alternatively, a Prevailing wind sluggish plug of cooler, partially solidifi ed lava may push up at the vent during an effusive eruption, creating a lava dome. A growing Eruption cloud u p t i o lava dome may become so steep that it E r n collapses, violently releasing pyroclastic fl ows l u m potentially as hazardous as those produced Tephra c o n during explosive eruptions. During and after an explosive or effusive (ash) eruption, loose volcanic debris on the fl anks of the volcano can be mobilized by heavy rainfall fall or melting snow and ice, forming powerful Lava dome fl oods of mud and rock (lahars) resembling Lava dome collapse Vent P y rivers of wet concrete. These can rush down r o c l valleys and stream channels as one of the most a s t i c destructive types of volcano hazards. w f l flo L o w tic a When a dormant volcano reawakens, las n Pyroc d sl a series of events commonly unfolds—the ide energy of eruptive activity increases, peaks, Lava flow and then gradually subsides as the volcano returns to a state of rest. The 1914 to 1917 Lahar (mud or debris flow) eruptions of Lassen Peak produced a yearlong Magma conduit series of minor steam blasts before a major explosion sent an eruption column 30,000 feet high and unleashed devastating pyroclastic fl ows and lahars. Windborne ash drifted 275 Volcanoes produce a variety of natural hazards that can damage infrastructure miles eastward and fell as far away as Elko, and negatively affect regional economies. This diagram shows the kinds of Nevada. The climactic phase of the eruption hazards that pose risks at volcanoes in California and elsewhere. Some hazards, was over in a matter of days, but recurring such as lahars and landslides, can occur even when a volcano is not erupting. steam blasts and lahars created hazardous Modified from “Geologic Hazards at Volcanoes” (USGS General Information conditions for several years afterwards. Product 64). Unlike other natural disasters, volcanic eruptions and their associated hazards can persist for months, years, or even decades before an “all clear” can be sounded. High to very high threat volcanoes. Several of California’s young volcanoes are less than 100 miles from major population centers. The inherent beauty of the State’s volcanic regions draws thousands of visitors each year, while their potential for geothermal energy has attracted industrial developers. Medicine Lake Volcano Mount Shasta Lassen Volcanic Center High threat Very high threat Very high threat Lava Beds National Monument, about 30 miles south This 14,162-foot-high volcano holds the Lassen Volcanic National Park, located about of Klamath Falls, Oregon, is located on the lower headwaters of the upper Sacramento 50 miles east of Redding, showcases the northern flank of the shield-shaped Medicine Lake River and is adjacent to several towns and dynamic history of this area and draws more Volcano and contains the highest concentration of major highway, rail, and air transportation than 350,000 visitors each year. Lassen Peak lava-tube caves in North America. corridors. erupted violently in the early twentieth century. The California Volcano Observatory uses several modern instrumental methods to monitor volcanoes. Three key techniques measure earthquakes (seismicity), movement of the ground surface (deformation), and the types and amounts of gases released from a volcano (gas geochemistry). Left: Sophisticated sensors like this Global Positioning System (GPS) receiver and seismometer in the Long Valley Volcanic Region can detect ground deformation and seismicity that occur as magma or volcanic gas rises toward the Earth’s surface in the weeks to months prior to an eruption. Data are telemetered from sensors in the field to USGS offices in Menlo Park, California, for processing and interpretation. Early detection of eruption precursors via a reliable volcano monitoring network is essential to hazard mitigation. Mammoth Mountain, a volcano made up of overlapping lava domes and flows, is visible behind the monitoring equipment. Right: Volcanic-gas “sniffer” at Mammoth Mountain continuously measures temperature plus carbon dioxide and other gas concentrations at a steaming vent. Volcano Hazard Zones Identify Statewide, California’s volcano CalVO Provides Timely Forecasting Threatened Areas. hazard zones encompass more than 24,000 of Volcano Hazards square miles, of which about half is Maps of volcano hazard zones convey privately owned and about half is public The mission of the California Volcano the types of hazards that may occur during a land that is managed by the U.S. Forest Observatory is to enhance public safety and future eruption and the areas of likely impact. Service, National Park Service, or Bureau minimize societal disruption in the event of The specifi c hazards to people and property of Land Management. Within these zones volcanic unrest through delivery of effective depend on the eruption style (effusive or are natural resources and infrastructure forecasts of volcanic activity derived from explosive), the volume of lava erupted, the essential to California’s water, power, monitoring and rigorous scientifi c research. location of the vent, the eruption duration, and transportation systems. Although less Whereas USGS maps of volcano hazard and local water-fl ow and precipitation than 1 percent of California’s population zones provide long-term perspectives on conditions. Low-energy effusive eruptions lives within a designated hazard zone, future volcanic activity, short-term forecasts are destructive, but generally not life more than 20 million recreational visitors give warning of likely outcomes under threatening.