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7.7: Predicting Volcanic Eruptions

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    What is one of the deadliest science jobs?

    No one can predict exactly when a volcanic eruption will take place. There are clues, but no one knows exactly when. Sometimes a volcano will erupt when scientists are studying it. Volcanologists have a high fatality rate among scientists because forecasting eruptions is so difficult.

    Predicting Volcanic Eruptions

    Volcanic eruptions can be devastating, particularly to the people who live close to volcanoes. Volcanologists study volcanoes to be able to predict when a volcano will erupt. Many changes happen when a volcano is about to erupt. Even so, eruptions are very difficult to predict.

    History of Volcanic Activities

    Scientists study a volcano’s history to try to predict when it will next erupt. They want to know how long it has been since it last erupted. They also want to know the time span between its previous eruptions. Scientists watch both active and dormant volcanoes closely for signs that show they might erupt.

    Picture of Mount Rainier in Washington

    Mount Rainier in Washington State is currently dormant. The volcano could, and probably will erupt again.


    Earthquakes may take place every day near a volcano. Before an eruption, the number and size of earthquakes increases. This is the result of magma pushing upward into the magma chamber. This motion causes stresses on neighboring rock to build up. Eventually the ground shakes. A continuous string of earthquakes may indicate that a volcano is about to erupt. Scientists use seismographs to record the length and strength of each earthquake.

    Slope Tilt

    All that magma and gas pushing upward can make the volcano’s slope begin to swell. Ground swelling may change the shape of a volcano or cause rock falls and landslides. Most of the time, the ground tilting is not visible. Scientists detect it by using tiltmeters, which are instruments that measure the angle of the slope of a volcano.


    Scientists measure the gases that escape from a volcano to predict eruptions. Gases like sulfur dioxide (SO2), carbon dioxide (CO2), hydrochloric acid (HCl), and water vapor can be measured at the site. Gases may also be measured from satellites. The amounts of gases and the ratios of gases are calculated to help predict eruptions.

    Remote Monitoring

    Satellites can be used to monitor more than just gases (Figure below). Satellites can look for high temperature spots or areas where the volcano surface is changing. This allows scientists to detect changes accurately and safely.

    Picture of Mount Cleveland in Alaska

    Mount Cleveland, in Alaska, is monitored by satellite.

    Costs and Benefits of Predictions

    No scientist or government agency wants to announce an eruption and then be wrong. There is a very real cost and disruption to society during a large-scale evacuation. If the scientists are wrong, people would be less likely to evacuate the next time scientists predicted an eruption. But if scientists predict an eruption that does take place, it could save many lives.


    • Volcanologists use several lines of evidence to try to forecast volcanic eruptions.
    • Magma moving beneath a volcano will cause earthquakes and slope deformation. Gases may be released from the magma out of the volcano vent.
    • Deciding whether to call for an evacuation is very tricky.


    1. What do scientists look for to see if a volcano might erupt someday?
    2. What are the signs that magma is moving beneath a volcano?
    3. For what characteristics is a volcano monitored remotely?
    4. Why is it helpful for scientists to be able to predict volcanic eruptions?

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