How can we predict the type of eruption?

Analysis of the seismic signature produced by a volcano can be used to predict what type of eruption will occur. 

Volcanoes produce two types of seismic signature, the first are called ‘volcanic earthquakes’, the other is ‘volcanic tremor’.

Small earthquakes occur, (volcanic earthquakes) when the rocks are broken by the magma moving through them . If the rocks are relatively cool and brittle the earthquake will be off a higher frequency than those that break hot-softer rocks, some times you will hear volcanologists talking about high or low frequency volcanic earthquakes.

   High frequency tremor

  Low frequency tremor

Pictures obtained from www.gns.cri.nz/what/earthact/volcanoes/hazards/monitor.htm without permission.

An almost continuous signal is seen when the hot volcanic gases that come from the magma pass through cracks on the way to the surface. They cause a small ground vibration, which is called volcanic tremor.  As the gas volume, velocity or pressure changes so does the strength of the signal. Volcanic tremor can also be caused by the movement of molten magma.

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