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Volcano Hazards Program
- Updated FAQs
- FAQs About Volcanic Eruptions
- example, within about 10 km)? Q: Can an eruption at one volcano trigger an eruption at another nearby volcano (for
- about the same time from volcanoes located hundreds to thousands of km apart? Q: Is there evidence for a cause and effect relationship between eruptions that occur at
- fault zones and nearby volcanic eruptions?......................................................................................... Q: Is there a relationship between large earthquakes (>M 6) that occur along major
- FAQ About Relationships Between Earthquakes and Volcanic Eruptions
- major fault zones and nearby volcanic eruptions? Is there a relationship between earthquakes larger than magnitude 6 that occur along
- Frequently Asked Questions About Volcano Monitoring
- Q: Why is it important to monitor volcanoes?
- Q: Why is monitoring volcanoes important to aviation?
- hazards? Q: Why is monitoring important for reducing risk from ground-based volcanic
- Q: How does the USGS monitor volcanoes in the United States?
- Q: How are volcanic thermal features measured?
- short notice? Q: Does the USGS have a team of volcanologists that can respond to volcanic unrest on
- Q: Does the USGS have a team for rapid response to volcano emergencies abroad?
- Q: How are earthquakes monitored?
- Q: How are ground movements measured?
- Q: How are volcanic gases measured?
- Q: What else do scientists measure at volcanoes?
- Frequently Asked Questions About Volcanic Hazards
- Q: What kinds of hazards are associated with volcanic eruptions?........................................
- Q: Can volcanoes be dangerous even when they don't erupt?..................................................
- Q: How can residents who live near volcanoes prepare for future eruptions?
- Q: How does the USGS provide eruption warnings?
- Q: How many active volcanoes are there in the United States?
- Q: How many active volcanoes are there on Earth?
- Frequently Asked Questions About Volcanoes in Movies.................................................
- Movies Fact or Fiction
- Q: Is the eruption depicted in Dante's Peak realistic?
- Q: Can eruptions really threaten helicopters, as in the movie, and other aircraft?
- eruptions? Q: Do earthquakes large enough to collapse buildings and roads accompany volcanic
- Q: Can a town's water supply become contaminated when a volcano is restless?
- Q: Do scientists drive across moving lava flows?
- Q: Can carbon dioxide gas from volcanoes kill trees and wildlife?
- signs of activity? Q: Can volcanoes suddenly become restless and erupt within one week of the first
- Q: Are robots used by the USGS to monitor volcanoes?
- time? Q: Can volcanoes produce large explosive eruptions and rivers of fluid lava at the same
- Q: Can lakes near volcanoes become acidic enough to be dangerous to people?
- FAQs About Studying and Working on Volcanoes
- Q: Are you "scared" when working on an active volcano?
- concluded the volcano is likely to erupt soon? Q: Are you scared when the volcano is showing signs of restless activity and you've
- Q: Is it dangerous to work on volcanoes and what precautions do scientists take?
- Q: What's it like to work on volcanoes?
- Q: What kind of school training do you need to become a volcanologist?...........................
- Q: What instruments, tools, and methods do you use to study volcanoes?
causes an eventual eruption at any one volcano, not the timing of significant eruptions hundreds to thousands of km apart. According to the theory of plate tectonics, the location and frequency of volcanism on Earth is due primarily to the way in which our planet's surface is divided into large sections or plates and how they move relative to each other, and the formation of deep "thermal plumes" that rise from the core-mantle boundary about 3,200 km below the surface. These mechanisms and the fact that even nearby volcanoes erupt magma with different and often unique chemical composition (evidence that each volcano has a separate unique shallow magma reservoir) strongly suggests there is unlikely to be any cause and effect relationship between volcanic eruptions separated hundreds to thousands of km apart.
Q: Is there a relationship between large earthquakes (>M 6) that occur along major
fault zones and nearby volcanic eruptions?
A: Sometimes, yes. A few historic large regional earthquakes (>M 6) are considered by scientists to be related to a subsequent eruption or to some type of unrest at a nearby volcano. The exact triggering mechanism for these historic examples is not well understood, but the volcanic activity probably occurs in response to a change in the local pressure surrounding the magma reservoir system as a consequence of (1) severe ground shaking caused by the earthquake; or (2) a change in the "strain" or pressure in the Earth's crust in the region surrounding where the earthquake occurred.
Historic Examples
Kilauea Volcano, Hawaii
1975 :
A large earthquake (7.2 on the Richter Scale) struck the Big Island of Hawaii at
4:48 a.m. on November 29, 1975. It was centered about 28 kilometers southeast
of Kilauea Volcano's summit caldera at a depth of 5 kilometers; the earthquake
occurred within the volcano's south flank. The earthquake was preceded by
numerous foreshocks, the largest of which was a 5.7 magnitude jolt at 3:36 the
same morning, and was accompanied, or closely followed, by a tsunamis
(seismic sea wave), massive ground movements, hundreds of aftershocks, and a
short-lived eruption in Kilauea's summit caldera.
The eruption began at 5:32 a.m. from a 500-meter long fissure on the caldera floor and ended by 10:00 p.m. According to scientists at the USGS Hawaiian Volcano Observatory, the eruptive activity "was apparently triggered by the 7.2 magnitude earthquake. The small volume and brief duration of the eruption suggest that the shallow magma might not have reached the surface under its own buoyant energy without a triggering mechanism apparently provided by the violent ground shaking." Source:
Tilling, Robert I., Koyanagi, Robert Y., Lipman, Peter W., Lockwood, John P., Moore, James G., and Swanson, Donald A., 1976, Earthquake and related catastrophic events, Island of Hawaii, November 29, 1975: A preliminary report: U.S. Geological Survey Circular 740, 33 p. 1868 :
The largest historic earthquake (estimated between 7.5 and 8.1) on the Big
Island occurred beneath the south flank of Mauna Loa Volcano on April 2, 1868.
The earthquake was followed by a small eruption from Kilauea's southwest rift
zone and from a fissure on the caldera wall that flooded the adjacent Kilauea Iki
crater with lava. Also, within Kilauea's caldera, part of the floor subsided about 90
meters. This activity occurred nearly simultaneously with an eruption from the
southwest rift zone of Mauna Loa volcano.
Source: Macdonald, Gordon A., Abbott, Agatin T., and Peterson, Frank L., 1983 (2nd edition), Volcanoes in the Sea -- The geology of Hawaii: Honolulu, University of Hawaii Press, 517 p.
Mount Pinatubo, Philippines
Mount Pinatubo's huge explosive eruption on June 15, 1991, occurred within 11 months of a magnitude 7.8 earthquake that occurred about 100 kilometers northeast of the volcano. Many scientists have since asked, "Was the eruption triggered by, or otherwise related to the earthquake that had occurred on July 16, 1990?" A recent study by scientists of the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey Study suggests that there was indeed a relationship between the two events. The study suggests that the "failure stress along faults of the Pinatubo area" after the big earthquake "were probably not a cause of Pinatubo's awakening. However, compressive stress on the magma reservoir and its roots was about 1 bar, possibly enough to squeeze a small volume of basalt into the overlying dacitic reservoir. Alternately, strong ground shaking associated with the Luzon earthquake might have done the same or triggered movement along previously stressed faults that in turn allowed magma ascent." Source: Bautista, B.C., Bautista, L.P., Stein, R.S., Barcelona, E.S., Punongbayan, R.S., Laguerta, E.P., Rasdas, A.R., Ambubuyog, G., and Amin, E.Q., Relationship of Regional and Local Structures to Mount Pinatubo Activity in: Newhall, C.G., Punongbayan, R.S. (eds.) Fire and mud: Eruptions and lahars of Mt. Pinatubo, Philippines, Philippine Institute of Volcanology and Seismology, Quezon City and University of Washington Press, Seattle p. 351- 370.
Restless Calderas
A recent study of the historic activity at calderas from around the world showed that "caldera unrest occurred at least 79 times in close temporal association with regional
FAQ About Relationships Between Earthquakes and
Volcanic Eruptions
Is there a relationship between earthquakes larger than magnitude 6 that occur along
major fault zones and nearby volcanic eruptions?
Dawn, November 29, 1975 - Spatter from a part of the fissure on Kīlauea caldera floor east of Halema‘uma‘u. After large earthquakes the question of whether such strong events can trigger nearby volcanic eruptions often comes up. The short answer to this question is: “not very often.” There are a few examples in the historical record that suggest a connection between large earthquakes and volcanic eruptions, but even these, on close inspection, do not show a simple causative relationship. The most unambiguous case of triggering is probably the November 29, 1975 magnitude (M) 7.2 Kalapana, Hawai‘i earthquake, which was immediately followed by a small, and short-lived eruption at Kīlauea volcano, Hawai‘i. However, in this case, the fault plane of the earthquake (i.e., the extent of the rupture) was directly beneath Kīlauea Volcano. Also, at the time of the earthquake, Kilauea was showing signs of pressurization and was likely poised to erupt soon anyway. Kīlauea is one of the most active volcanoes in the world, and erupted frequently in the decades before and after the 1975 earthquake.
May 24, 1960 - Ash-laden eruption plumes rise above fissure vent at Puyehue-Cordón Caulle, Chile. Photo by Oscar Gonzá-Ferrán (University of Chile). Archived with the Global Volcanism Program. Another example of possible triggering occurred after the M9.5 Chile earthquake on May 22,
- About 38 hours after the mainshock, Puyehue-Cordón Caulle in Central Chile erupted violently after being inactive for more than 25 years. In this instance, as at Kīlauea above, it is likely that the fault rupture extended beneath the volcano. Establishing a statistical correlation between large earthquakes and subsequent volcanic eruptions requires a long and accurate record of both seismic and volcanic activity. The global record of such activity is sparse, especially for events that occurred before 1900. While there are hints of connections in some cases, and a few convincing anecdotes, statistical analyses to date have shown only a weak correlation. And, even if a statistical correlation is shown, working to establish and explain a causal connection is another matter entirely. There are speculations in the literature, some backed by detailed experiments, about what mechanisms might be behind volcanic triggering by large earthquakes. Mechanisms under consideration include:
- Stress changes caused by large earthquakes may either compress or expand nearby magma reservoirs. In the former case, the compression could increase the reservoir pressure, while in the latter case, the
Donne DD, Harris AJL, Ripepe M, and Wright R, 2010. Earthquake-induced thermal anomalies at active volcanoes, Geology, v.38 n.9, p.771-774. Eggert S and Walter TR, 2009. Volcanic activity before and after large tectonic earthquakes: Observations and statistical significance, Tectnophysics, v.471 p.14-26. Hill DP, Pollitz F, and Newhall C, 2002. Earthquake-volcano interactions: Physics Today, v.55, n.11, p.41-47. Husen S, Wiemer S, and Smith RB, 2004. Remotely triggered seismicity in the Yellowstone National Park region by the 2003 Mw7.9 Denali fault earthquake, Alaska, Bulletin of the Seismological Society of America, v.94, n.6B, p.S317-S331. Johnston MJS, Prejean SG, and Hill DP, 2004. Triggered deformation and seismic activity under Mammoth Mountain in Long Valley caldera by the 3 November 2002 Mw7.9 Denali fault earthquake, Bulletin of the Seismological Society of America, v.94, n.6B, p.S360-S369. Lara LE, Naranjo JA, and Moreno H, 2004. Rhyodacitic fissure eruption in Southern Andes (Cordon Caulle; 40.5° S) after the 1960 (Mw:9.5) Chilean earthquake: a structural interpretation, Journal of Volcanology and Geothermal Research, v.138, p.127-138. Macdonald GA, Abbott AT, and Peterson FL, 1983. Volcanoes in the Sea -- The geology of Hawaii (2nd edition), Honolulu, University of Hawaii Press, 517 p. Walter TR, Wang R, Zimmer M, Grosser H, Luhr B, and Ratdomopurbo A, 2007. Volcanic activity influenced by tectonic earthquakes: Static and dynamic stress triggering at Mt. Merapi, Geophysical Research Letters, v.34 L05304. Manga M and Brodsky E, 2006. Seismic Triggering of Erutpions in the Far Field: Volcanoes and Geysers, Annual Review of Earth and Planetary Sciences, v.34, p.263-291. Newhall CG and Dzurisin D, 1988. Historic Unrest at Large Calderas of the World, U.S. Geological Survey Bulletin 1855, v.1, p.19-20. Pozgay SH, White RA, Weins DA, Shore PJ, Sauter AW, and Kaipat JL, 2005. Seismicity and tilt associated with the 2003 Anatahan eruption sequence, Journal of Volcanology and Geothermal Research, v.143, i.1-3, p.60-76. Tilling RI, Koyanagi RY, Lipman PW, Lockwood JP, Moore JG, and Swanson, DA, 1976. Earthquake and related catastrophic events, Island of Hawaii, November 29, 1975: A preliminary report: U.S. Geological Survey Circular 740, 33p.
White RA and Harlow DH, 1993. Destructive upper-crustal earthquakes of Central America since 1900, Bulletin of the Seismological Society of America, v.83, n.4, p.1115- 114 2. White RA and Power JA, 2001. Distal volcano-tectonic earthquakes (DVT's): Diagnosis and use in eruption forecasting, Eos Transactions AGU, 82(47), Fall Meeting Supplement, Abstract #U32A-00012.
Frequently Asked Questions About Volcano Monitoring
To anticipate the awakening or reawakening of a volcano, volcanologists watch for changes caused by moving or pressurizing magma and associated changes in the hydrothermal system surrounding the magma. Magma moving toward the surface can cause swarms of earthquakes; swelling, subsidence, or cracking of the volcano's flanks; and changes in the amount or types of gases that are emitted from a volcano. The USGS continuously monitors many volcanoes in the states of Washington, Oregon, California, Hawaii, Alaska, and Wyoming (Yellowstone) to detect unusual activity.
Q: Why is it important to monitor volcanoes?
A: The United States and its territories contain 169 geologically active volcanoes, of which 54 volcanoes are a very high or high threat to public safety [National Volcano Early Warning System (NVEWS)]. Many of these volcanoes have erupted in the recent past and will erupt again in the foreseeable future. As populations increase, areas near volcanoes are being developed and aviation routes are increasing. As a result, more people and property are at risk from volcanic activity. Future eruptions could affect hundreds of thousands of people. To help prevent loss of life and property, the U.S. Geological Survey and its partners monitor these volcanoes, and issue warnings of impending eruptions. Real-time monitoring of volcanoes, with the use of volcano seismology, gas, thermal, and surface deformation measurements, permits scientists to anticipate with varying degrees of certainty, the style and timing of an eruption. While our present state of knowledge does not allow us to predict the exact time and place of eruptions, we can detect changes from usual behavior that precede impending eruptions. We communicate these changes in our volcano updates. The information in the volcano updates allows scientists, public officials, and people in communities at risk to make preparations that can reduce losses during an eruption. Because volcanoes can erupt with little warning, continuous monitoring is important even if a volcano is not showing signs of activity.
Q: Why is monitoring volcanoes important to aviation?
A: Most of the U.S. volcanoes can pose a serious hazard to domestic and/or international aviation. Below is a summary of KLM Flight 867, a Boeing 747 with more than 240 passengers aboard, that encountered ash from the 1989 eruption of Mt. Redoubt near Anchorage, Alaska. The ash encounter provides an example of how volcano monitoring is important to domestic and international aviation. The following account is summarized by Captain Terry McVenes, Executive Air Safety Chairman Air Line Pilots Association, International before the Committee on Commerce, Science, and Transportation Subcommittee on Disaster Prevention and Prediction. U.S. SENATE March 16, 2006. To classify this encounter as one presenting grave danger for those 240 passengers and that crew is an understatement! All four engines of this aircraft failed within 59 seconds! A false cargo compartment fire warning indication required special attention by the crew. All normal airspeed indications failed! The
avionics compartments containing all of the radio, radar, electronic systems monitoring, and communications systems, all overheated and individual systems failed. The sophisticated electronic cockpit displays became an electronic nightmare [and the cockpit filled with smoke]. While ash was contaminating the engines and causing them to flame out, it was also contaminating electrical compartments and shorting electronic circuit boards. This four engine jumbo jet was essentially a glider for several minutes until the crew was able to individually re-start engines. Three of the engines eventually re-started but delivered reduced performance. The fourth engine eventually came on line when the aircraft was on final approach to Anchorage. Although the crew landed safely, the encounter caused $80 million dollars damage to the airplane. Under only slightly different circumstances, 240 plus fatalities and a total hull loss could have been the result. KLM 867 was only one of several commercial aircraft exposed to varying amounts of damage during several days of volcanic activity from Mt. Redoubt. Anchorage is one of the world's busiest airports for both passengers and cargo. The eventual economic impact of aircraft damages, cargo delays, passenger flight delays and cancellations, and general disruption to the Alaskan economy was staggering. Every commercial aviation operation in or through that territory suffered economic consequences. The USGS works with the Federal Aviation Association to provide information about volcanic unrest and potential eruptions. The information is used to reroute flights and reduce the risk of future ash encounters. For more information, please see the Volcanic Ash Site.
Q: Why is monitoring important for reducing risk from ground-based volcanic hazards?
A: U.S. communities on or near volcanoes are at risk from ground-based volcanic hazards that can quickly destroy towns, disrupt communication, and shut off transportation routes. By monitoring volcanoes, the people who live, work, and play, near the volcano slopes can be notified when the volcano awakens and take proper precautions that will minimize the volcano's disruption to their lives. Volcanic eruptions commonly begin with the explosion of gases that force billions of pieces of rock (ash) high into the sky. Ash in the atmosphere is a hazard to aviation (see Why is monitoring volcanoes important to aviation?). Once it falls to the ground, ash can interfere with systems for telecommunications, transportation, water, sewer and power, and can have a detrimental effect on agriculture and human health, even at great distances from the volcano (see the Volcanic Ash Site). Ground-based ash hazards can persist for months or years when resuspended by wind or human activity. More than one billion dollars ( dollars) in losses resulted from the 1980 eruption of Mount St. Helens, and much of the loss was from volcanic ash. Volcanic eruptions often continue with the eruption of lava. As the lava flows down the steep slopes it often breaks apart into a billowing avalanche of hot rock and gas, called a pyroclastic flow. Pyroclastic flows destroy anything in their path. In 1902 a pyroclastic flow from Mount Pelee in the West Indies killed 30,000 people in the nearby town of St. Pierre in a matter of minutes.
Q: How are earthquakes monitored?
A: By installing seismometers that send information continuously via radio to a central recording site (observatory), scientists can determine the sizes and locations of earthquakes near a volcano. They look for specific types of earthquakes that are often associated with volcanic activity, including long- period volcanic earthquakes and volcanic tremor. For more information, please see Monitoring Volcano Seismicity.
Q: How are ground movements measured?
A: Ground deformation (swelling, subsidence, or cracking) is measured with a variety of techniques, including Electronic Distance Meters (EDM), the Global Positioning System (GPS), precise leveling surveys, strainmeters, and tiltmeters. EDMs use lasers to accurately measure changes in distance between benchmarks (fixed points) with repeated measurements. GPS makes use of satellites orbiting the Earth to determine and track the locations of points. Strainmeters and tiltmeters are used to monitor subtle changes in shape of the ground surface. For more information, please see Monitoring Volcano Ground Deformation.
Q: How are volcanic gases measured?
A: Instruments to measure sulfur dioxide and carbon dioxide can be mounted in aircraft to determine the quantity of gas being emitted on a daily basis. Such instruments can also be used in a ground-based mode. An instrument that detects carbon dioxide can be installed on a volcano and configured to send data continuously via radio to an observatory. Sulfur dioxide in volcanic clouds can also be measured from space with instruments aboard satellites. For more information, please see Monitoring Volcanic Gases.
Q: What else do scientists measure at volcanoes?
A: Field observations by experienced volcanologists go hand in hand with more sophisticated equipment and techniques to form a complete system for monitoring volcanoes. Field observations may include water temperature and pH (acidity) measurements, or observations of ground cracking and new areas of avalanching rocks. An experienced observer can integrate many different types of data on the spot and design simple measurements to further assess the significance of volcanic unrest. There is no substitute for well-trained, experienced observers when trying to figure out how a volcano will behave. For additional information, please see Hydrologic Monitoring of Volcanoes.
Frequently Asked Questions About Volcanic Hazards
A restless volcano endangers any nearby residents with clouds of ash, falling blocks of rock, pyroclastic flows or ash hurricanes, lava flows, and floods of debris or lahars. These hazards are typical of snow- and ice-covered stratovolcanoes like those in the Pacific Northwest and Alaska. Since 1980, volcanic activity has killed more than 29,000 people worldwide. Most of the deaths were caused by lahars and pyroclastic flows; a few hundred people were killed by ash falls, which collapsed the roofs of buildings.
Q: What kinds of hazards are associated with volcanic eruptions?
A: Debris flows, or lahars, are slurries of muddy debris and water caused by mixing of solid debris with water, melted snow, or ice. Lahars destroyed houses, bridges, and logging trucks during the May 1980 eruption of Mount St. Helens, and have inundated other valleys around Cascade volcanoes during prehistoric eruptions. Lahars at Nevado del Ruiz volcano, Colombia, in 1985, killed more than 23,000 people. At Mount Rainier, lahars have also been produced by major landslides that apparently were neither triggered nor accompanied by eruptive activity. Lahars can travel many tens of miles in a period of hours, destroying everything in their paths. Tephra (ash and coarser debris) is composed of fragments of magma or rock blown apart by gas expansion. Tephra can cause roofs to collapse, endanger people with respiratory problems, and damage machinery. Tephra can clog machinery, severely damage aircraft, cause respiratory problems, and short out power lines up to hundreds of miles downwind of eruptions. Explosions may also throw large rocks up to a few miles. Falling blocks killed people at Galeras Volcano in Colombia in 1992, and at Mount Etna, Italy, in 1979. Pyroclastic surges and flows are hot, turbulent clouds of tephra (known as surges), or dense, turbulent mixtures of tephra and gas (known as flows). Pyroclastic flows and surges can travel more than a hundred miles per hour and incinerate or crush most objects in their path. Though most extend only a few miles, a pyroclastic surge at Mount St. Helens in 1980 extended 18 miles (28 km) and killed 57 people. Pyroclastic surges at El Chichón volcano in Mexico in 1982 killed 2000 people, and pyroclastic flows at Mount Unzen, Japan, in June, 1991, killed 43 people. Speeding vehicles cannot outrun a pyroclastic flow or surge. Lava flows erupted at explosive stratovolcanoes like those in the Pacific Northwest and Alaska are typically slow-moving, thick, viscous flows. Kilauea volcano on the Island of Hawaii has produced thin, fluid lava flows throughout its history, and almost continuously since 1983. Lava flows destroyed a visitor center at Kilauea in 1989 and overran the village of Kalapana on the volcano's southeast flank in 1991.
volcano in Hawaii is one of the most active volcanoes on Earth. It has been erupting almost continuously since 1983!
Q: How many active volcanoes are there on Earth?
A: There are about 1500 potentially active volcanoes worldwide, aside from the continuous belt of volcanoes on the ocean floor. About 500 of these have erupted in historical time. Many of these are located along the Pacific Rim in what is known as the "Ring of Fire." In the U.S., volcanoes in the Cascade Range and Alaska (Aleutian volcanic chain) are part of the Ring, while Hawaiian volcanoes form over a "hot spot" near the center of the Ring.
Frequently Asked Questions About Volcanoes in
Movies
Movies Fact or Fiction
Dante's Peak, a volcano-disaster thriller from Universal Studios, dramatizes some real- world concerns faced by communities located near active volcanoes in the United States. Set in the northern Cascade Range of Washington State, the movie portrays the roles of U.S. Geological Survey (USGS) scientists and local public officials during the reawakening and eruption of a fictional volcano - one that resembles dozens of real volcanoes in Alaska, British Columbia, Washington, Oregon, and northern California. To separate fact from fiction, here are answers to some frequently asked questions about the movie and the USGS mission to reduce the risk from dangerous volcanoes.
Q: Is the eruption depicted in Dante's Peak realistic?
A: In many but not all respects, the movie's depiction of eruptive hazards hits close to the mark, especially as regards the enormous power unleashed during an eruption. Stratovolcanoes in the Cascade Range and Alaska erupt explosively and produce pyroclastic flows, clouds of volcanic ash, and debris flows (lahars) that behave much as shown in the movie. Lava flows at these volcanoes, though, are usually thick and slow moving, unlike the fluid flows in the movie. Fast-flowing flows of basalt lava are common in Hawaii, though. Real eruptions may be considerably larger or smaller, and affect larger or smaller areas, than those shown in the film.
Q: Can eruptions really threaten helicopters, as in the movie, and other aircraft?
A: Yes. Encounters between aircraft and clouds of volcanic ash are a serious concern. Jet engines and other aircraft components are vulnerable to damage by fine, abrasive volcanic ash, which can drift in dangerous concentrations hundreds of miles downwind from an erupting volcano. In the past, many aircraft have accidentally encountered volcanic ash clouds, and in some cases jet engines have temporarily lost power. An international consortium of government agencies, including the U.S. Geological Survey, Federal Aviation Administration, and National Weather Service, now monitors ash-producing volcanoes and tracking volcanic ash clouds to reduce the likelihood of future encounters.
Q: Do earthquakes large enough to collapse buildings and roads accompany volcanic
eruptions?
A: Not usually. Earthquakes associated with eruptions rarely exceed magnitude 5, and these moderate earthquakes are not big enough to destroy the kinds of buildings, houses, and roads that were demolished in the movie. The largest earthquakes at Mount St. Helens in 1980 were magnitude 5, large enough to sway trees and damage buildings, but not destroy them.
