How can we tell when a volcano will erupt?

Most volcanoes provide warnings before an eruption. Magmatic eruptions involve the rise of magma toward the surface, which normally generates detectable earthquakes. It can also deform the ground surface and cause anomalous heat flow or changes in the temperature and chemistry of the groundwater and spring waters. Steam-blast eruptions, however, can occur with little or no warning as superheated water flashes to steam.

Notable precursors to an eruption might include:

  • An increase in the frequency and intensity of felt earthquakes
  • Noticeable steaming or fumarolic activity and new or enlarged areas of hot ground
  • Subtle swelling of the ground surface
  • Small changes in heat flow
  • Changes in the composition or relative abundances of fumarolic gases

These precursors do not indicate the type or scale of an expected eruption (that information is best obtained by mapping previous eruptions). Precursors can continue for weeks, months, or even years before eruptive activity begins, or they can subside at any time and not be followed by an eruption. Italy’s Campi Flegrei volcano has been showing signs of unrest for over 60 years.

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Mount St. Helens 2004-2008 Eruption: A Volcano Reawakens

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A gas plume arising from Augustine Volcano during it's eruptive phase 2005-06.
January 24, 2006

A gas plume arising from Augustine Volcano during it's eruptive phase 2005-06.

A gas plume arising from Augustine Volcano during it's eruptive phase 2005-06. This photo was taken during  a FLIR/maintenance flight on January 24, 2006.

Image: Augustine Volcano
January 12, 2006

Augustine Volcano

Augustine volcano viewed from the west.

 

Attribution: Natural Hazards