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 (1980 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.

On snow-covered volcanoes, a pyroclastic flow churns and melts snow and glacier ice which forms a slurry of boulders, mud, and water called a lahar. Lahars can sweep down valleys to great distances from the volcano. In 1985, lahars formed during the eruption of Nevado del Ruiz in Colombia killed 23,000 people within four hours of the beginning of the eruption. The use of real-time lahar-detection systems in valleys where large populations are at risk, such as near Mount Rainier, can provide warning of the occurrence of a lahar, and valuable extra minutes for evacuation. For more information, please see the Volcano Hazards page.

Q: How does the USGS monitor volcanoes in the United States?

A: In cooperation with universities and state agencies, the USGS monitors seismic activity, ground deformation, volcanic gases, thermal emissions, and changes in water levels and chemistry. When unusual activity is detected, a response team may do more ground surveys and install more instruments, if possible, to better determine if an eruption is likely.

Q: How are volcanic thermal features measured?

A: USGS scientists use instruments in the field and mounted on aircraft and satellites to measure surface temperatures and geothermal heat flux and look for thermal anomalies that may be precursor to an eruption or indicative of significant changes during an on-going eruption. Satellite-based thermal measurements can be made on a regular basis for near-real time thermal monitoring of any volcano in the world. Higher-resolution field-based and aircraft-based thermal measurements can be made episodically to understand the spatial details of thermal features.

Q: Does the USGS have a team of volcanologists that can respond to volcanic unrest on short notice?

A: Yes. The USGS Volcano Hazards Team includes experts in all aspects of volcano hazard assessment, monitoring, information dissemination, and volcano-emergency response.

Q: Does the USGS have a team for rapid response to volcano emergencies abroad?

A: Yes. Such a team is operated by the U.S. Geological Survey as part of the Volcano Disaster Assistance Program (VDAP). The team was formed in cooperation with the Office of U.S. Foreign Disaster Assistance (OFDA) of the U.S. Agency of International Development (USAID) following the 1985 eruption of Nevado del Ruiz Volcano, Colombia, in which over 23,000 people lost their lives. At the request of host countries and working through OFDA, VDAP scientists quickly determine the nature of volcanic unrest and assess its possible consequences. VDAP has responded to volcano emergencies in more than a dozen countries during the past decade.

In addition to helping people in other countries to get out of harm's way, VDAP's international work directly benefits volcano-hazard mitigation in the United States. Through VDAP, we gain experience at active volcanoes that will help during future crises in the western United States, and we collect important scientific data on eruption precursors that are used to better understand how U.S. volcanoes work.

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 in our Activity Section.

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 in our Activity Section.

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 in our Activity Section.

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 in our Activity Section.