How closely are earthquakes related to volcanoes?
Joshua
Dear Joshua,
Some, but not all, earthquakes are related to volcanoes. For example,
most earthquakes are along the edges of tectonic plates. This is where
most volcanoes are too. However, most earthquakes are caused by the
interaction of the plates not the movement of magma.
Most earthquakes directly beneath a volcano are caused by the movement of
magma. The magma exerts pressure on the rocks until it cracks the rock.
Then the magma squirts into the crack and starts building pressure
again. Every time the rock cracks it makes a small earthquake. These
earthquakes are usually to weak to be felt but can be detected and
recorded by sensitive instruments. Once the plumbing system of the
volcano is open and magma is flowing through it, constant earthquake
waves, called harmonic tremor, are recorded (but not felt).
Steve Mattox, University of North Dakota
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