As described in the box on page 43, volcanic eruptions are the culmination of a complex ensemble of processes. An eruption is preceded by the buildup of pressure in the chamber in which magma has pooled within the crust. As the magma in the chamber cools, crystals form and volatile compounds trapped within the remaining melt exsolve to form bubbles. When the pressure in the chamber approaches a critical value, the volatile-rich magma at the top of the chamber will begin breaching the chamber’s roof with sheetlike intrusions, some of which may reach the surface in a volcanic eruption.
The events leading to an eruption are manifested as episodes of volcanic unrest, characterized by swarms of earthquakes, ground deformation, and excitation of the hydrothermal system as the magma heats groundwater in the upper part of the crust. Multiple episodes of volcanic unrest of increasing frequency and intensity typically precede eruptions. Unrest episodes outnumber eruptions by as much as an order of magnitude 2. Volcanic systems that have evolved to a critical state are most susceptible to small perturbations produced by a distant earthquake. For that reason, seismologists and volcanologists are interested not only in the triggering of volcanic eruptions but also in the triggering of episodes of volcanic unrest, which may be early symptoms of an impending volcanic eruption
http://earthweb.ess.washington.edu/lnk/ess-462/reading/hill-pollitz-newhall-proof.pdf
18.59, 17.08.12.
Earthquakes related to volcanic activity may produce hazards which include ground cracks, ground deformation, and damage to manmade structures. Earthquakes produced by stress changes in solid rock due to the injection or withdrawal of magma (molton rock) are called volcano-tectonic earthquakes . These earthquakes can cause land to subside and can produce large ground cracks. These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present. Volcano-tectonic earthquakes don't indicate that the volcano will be erupting but can occur at anytime.When magma injection is sustained a lot of earthquakes are produced (Chouet, 1993). This type of activity indicates that a volcano is about to erupt. The signal is known as volcanic tremor.
People living near an erupting volcano are very aware of volcanic earthquakes. Their houses will shake and windows rattle from the numerous earthquakes that occur each day before and during a volcanic eruption. Residents in Pompeii felt earthquakes daily before Vesuvius erupted in A.D. 79 but continued to go about their daily routines (Francis, 1993). Earthquakes exhibiting volcanic tremor warn of an impending eruption so that people can be evacuated to areas of safety. The volcanic tremor signal has been used successfully to predict the 1980 eruptions Mount St. Helens. Volcano-tectonic earthquakes can cause damage to manmade structures and landsliding. Structures should be built according to earthquake standards, on firm ground and not unconsolidated material which may amplify earthquake intensity
Earthquakes related to volcanic activity may produce hazards which include ground cracks, ground deformation, and damage to manmade structures. Earthquakes produced by stress changes in solid rock due to the injection or withdrawal of magma (molton rock) are called volcano-tectonic earthquakes . These earthquakes can cause land to subside and can produce large ground cracks. These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present. Volcano-tectonic earthquakes don't indicate that the volcano will be erupting but can occur at anytime.When magma injection is sustained a lot of earthquakes are produced (Chouet, 1993). This type of activity indicates that a volcano is about to erupt. The signal is known as volcanic tremor.
People living near an erupting volcano are very aware of volcanic earthquakes. Their houses will shake and windows rattle from the numerous earthquakes that occur each day before and during a volcanic eruption. Residents in Pompeii felt earthquakes daily before Vesuvius erupted in A.D. 79 but continued to go about their daily routines (Francis, 1993). Earthquakes exhibiting volcanic tremor warn of an impending eruption so that people can be evacuated to areas of safety. The volcanic tremor signal has been used successfully to predict the 1980 eruptions Mount St. Helens. Volcano-tectonic earthquakes can cause damage to manmade structures and landsliding. Structures should be built according to earthquake standards, on firm ground and not unconsolidated material which may amplify earthquake intensity
http://www.geo.mtu.edu/volcanoes/hazards/primer/eq.html
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