Volcano monitoring
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Volcano monitoring. Based on: USGS Volcano Hazards program http://volcanoes.usgs.gov/activity/methods/index.php. Volcano monitoring methods. Designed to detect and measure changes caused by magma movement beneath a volcano Rising magma typically cause: Seismic events

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Volcano monitoring

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Volcano monitoring

Based on: USGS Volcano Hazards program

http://volcanoes.usgs.gov/activity/methods/index.php


Volcano monitoring methods

Designed to detect and measure changes caused by magma movement beneath a volcano

Rising magma typically cause:

  • Seismic events

  • Swelling or subsidence of the summit or flank of a volcano

  • Release of volcanic gases


Questions typically addressed in volcano monitoring:

  • Does the current unrest involve the movement of magma?

  • If yes, when is an eruption most likely to occur, if at all?

  • During an eruption, what real-time warnings are needed to prevent loss of life and property damage?

  • When is the eruption really over?


Other questions…:

  • What is the nature of a volcano's magma-reservoir system?

  • What is the cause of specific volcano-seismic events?

  • How do volcanic ash clouds disperse downwind of an erupting volcano?

  • How susceptible to massive slope failures (landslides) are volcanoes?


Monitoring method: Seismicity

Magma rises into reservoir beneath volcano

Rising magma and gases exert pressure

High pressure causes rocks to break, triggering earthquakes


  • Earthquake activity beneath a volcano almost always increases before an eruption

  • When magma and gases move they either cause rocks to break (results in HIGH-FREQUENCY earthquakes)

  • Or they can cause cracks to vibrate (results in LOW-FREQUENCY earthquakes or continuous shaking called volcanic tremors)


  • Most volcanic-related earthquakes are less than a magnitude 2 or 3 and occur less than 10 km beneath a volcano.

  • The earthquakes tend to occur in swarms consisting of dozens to hundreds of events


Webicorder record for Redoubt volcano, March 27, 2009


The surface of a volcano often changes shape when magma moves beneath it or rises into its cone

The ground can change shape by rising up, subsiding, tilting, or forming bulges

Monitoring method: Ground deformation

Illustration by B. Myers and S. Brantley


Methods for monitoring volcano ground deformation

  • Electronic Distance Measurement (EDM)

    Measures distance between benchmarks placed on a volcano using electromagnetic signals

  • Tiltmeters (one of the oldest methods)

    Measures changes in the slope angle or “tilt” of the ground due to magma movement


  • Global Positioning System (GPS)

    Measures horizontal as well as vertical ground motions using satellite transmission

    Signals from at least 4 satellites is essential for accuracy

    More accurate and convenient that EDM


Satellite Radar Inferometry (INSAR)


Satellite images taken before and after deformation are combined

Changes in satellite-to-ground distance can be identified in mm scale.

Unlike other methods, INSAR technique provides information regarding overall pattern of deformation of a volcano


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