Cascades Volcano Observatory, Vancouver, Washington

• Can scientists really anticipate volcanic eruptions?
• Are specific predictions of an eruption's time, place, and character possible?
• Is there really a U.S. Geological Survey and does it provide eruption warnings?
• How does the USGS provide eruption warnings?
• How many active volcanoes are there in the United States?
• How many active volcanoes are there on Earth?
• What are the major volcanoes in the Cascade Range?
• Which Cascade volcano will erupt next?

• Is the eruption depicted in Dante's Peak realistic?
• Can eruptions really threaten helicopters, as in the movie, and other aircraft?
• Can the temperature of hot springs near a restless volcano change quickly enough to injure bathers?
• Do earthquakes large enough to collapse buildings and roads accompany volcanic eruptions?
• Can a town's water supply become contaminated when a volcano is restless?
• Do scientists drive across moving lava flows?
• Can carbon dioxide gas from volcanoes kill trees and wildlife?
• Can volcanoes suddenly become restless and erupt within one week of the first signs of activity?
• Are robots used by the USGS to monitor volcanoes?
• Can volcanoes produce large explosive eruptions and rivers of fluid lava at the same time?
• Can lakes near volcanoes become acidic enough to be dangerous to people?

Before a volcano erupts, magma must force its way upward through solid rock beneath a restless volcano. This process causes the ground above to heave and shake as rock is shoved aside or broken. At the same time, gases are released from the magma as it rises to shallower levels where the pressure is lower. These phenomena - ground movements, earthquakes, and changes in volcanic gases - provide the clues that scientists use to recognize a restless volcano and anticipate what might happen next.

• What kinds of unusual activity might be noticed before an eruption?
• What is volcanic tremor, and how does it differ from earthquakes?
• Do volcanoes produce different kinds of earthquakes?
• What kind of gases escape from volcanoes?
• Are there any restless volcanoes in the U.S. today?

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. Much as depicted in Dante's Peak, 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.

• Does the USGS have a team of volcanologists that can respond to volcanic unrest on short notice?
• Does the USGS have a team for rapid response to volcano emergencies abroad?
• How does the USGS monitor volcanoes in the United States?
• How are earthquakes monitored?
• How are ground movements measured?
• How are volcanic gases measured?
• Can mudflows be monitored?
• What else do scientists measure at volcanoes?

In Dante's Peak, a restless volcano endangers 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.

• What kinds of hazards were depicted in the movie, and what part have they played in real volcanic eruptions?
• Can volcanoes be dangerous even when they don't erupt?
• How can residents who live near volcanoes prepare for future eruptions?

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