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4.2

Triggers are unique to each volcano and the geology and geography of the system.

The vulnerability to each trigger varies for each volcano.The first key to eruptions is  eruption type which is dependent on the composition of the magma to be erupted.  This depends mainly on the viscosity and volatile content which determine how explosive an eruption will be, and how much overpressure can develop before the volcano erupts.

Multiple environmental factors exist which impact the types of triggers which occur at each volcano.  Steepness of the slope and height of the volcano determine whether or not landslides or glacial melt triggers are possible or likely..  A composite volcano along a convergent plate boundary is likely to be tall and steep sided making flank collapse a threat. They are also susceptible to earthquakes, and may produce explosive eruptions. Their high elevations may produce glaciers which can melt and cause phreatic eruptions. A shield volcano, on the other hand, is broad meaning flank collapse is unlikely.  Also these volcanoes are less likely to experience high magnitude earthquakes since they are located over hot spots and rift zones which do not produce these large quakes.  Latitude also contributes to this complexity. A shield volcano in Hawaii does not have the issue of glaciers and thick snow pack where as one in Iceland does.  For a complete overview of volcano types and their locations on plate boundaries, read This from Tulane University.

Certain triggers are, however, more common than others.  Most explosive eruptions are mobilized by some form of magma mixing which creates the initial instability and overpressure. Earthquakes are common destabilizing events because volcanoes are often located along plate boundaries.  Glaciers are not present on many volcanoes in warmer climates unless their elevation is high enough to maintain a constant snow cap.  This complexity makes volcanic trigger monitoring difficult and specific to each volcano.

Examples:

The eruption of Eyjafjallajokull occurred partially along fissures which are triggered almost entirely by mobilized magma from magma mixing.

The eruption of Mt. Saint Helens was much more complex involving magma mixing, earthquakes, contact with water table from glacial melt, and flank collapse triggers.

Pacaya is a Volcano in Guatemala which is at risk for flank collapse due to its steep sides and high activity. Earthquakes are common here due to its location near a variety of plate boundaries. It has no glaciers so this is not a trigger factor.

 

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