MadSci Network: Earth Sciences

Re: Can volcano get rid of high silica buildup without a large explosion?

Date: Fri Mar 18 10:35:36 2005
Posted By: David Kopaska-Merkel, Staff Economic Geology Division
Area of science: Earth Sciences
ID: 1110484560.Es

Mount St. Helens is a stratovolcano, and these volcanoes usually erupt 
explosively.  A brief summary of their characteristics can be found here:
That pamphlet, from the US Geological Survey, mentions that some stratovolcanoes 
erupt basalt and that these tend not to erupt explosively.  However, your 
question was specifically about high-silica volcanoes and those are not  
basaltic. Here is another summary of stratovolcano characteristics:
That page explains that stratovolcanoes tend to be composed of about half lava 
and half pyroclastic debris.  This means that in terms of the volume 
produced, about half of the eruptions are not explosive.  In other words, 
this kind of volcano can erupt relatively calmly, but any such volcano is 
going to erupt explosively some of the time. The composition of the magma 
in a given stratovolcano can vary quite a lot:
...and this is the cause of variation in the kind of eruption of a single
volcano.  The calmer eruptions from stratovolcanoes probably occur when the
silica content of the magma is lower.

An Internet search using google or another search engine will yield many 
other sites with information about this kind of volcano.

David C. Kopaska-Merkel
Geological Survey of Alabama
box 869999
Tuscaloosa, AL 35486

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