Most volcanoes hot enough to erupt 'less than 1% of the time' - breakthrough study

Feb 17, 2014 | Posted by: roboblogger | Full story: Russia Taday

Scientists now have a much better chance of finding out if a dormant volcano is about to erupt, after discovering that most of them contain magma that's hot and liquid enough for an eruption only for a small fraction of their lifetimes.

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“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

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#1
Feb 19, 2014
 
This ported over from another thread...

Nice, but old knowledge.

The only new bit here is the volcano under study with dacite in the magma chamber (Mt Hood), and the residence time of the Plagioclaise crystals in the magma chamber before eruption.

In general arc stratovolcanoes have a relatively predictable structure @ depth.
1:) the deepest part of ALL arc volcanoes is a fracture set at the base of the crust or upper mantle in the overriding plate. This fracture set is re charged by crustal relaxation megathrust events such as the 2004 S.Andaman event or the 2011 Tohoku event characterised by the megathrust letting go aft, & both plates relaxing with the resulting volume change in the trench causing a bloody great big tsunami. The fracture set is a network of fractures of varying lengths generally perpendicular to the vector of the runout of crustal relaxation. The result of such a megathrust is an immediate recharge of the fracture set. Recompression of the arc drives magma sideways along the fractures away from the point of greatest recompression rate. The magma eventually hits a "wall" near a segment boundary transform fault, or the arc graben fault depending on the recompression vector & the orientation of the fracture. With nowhere to go sideways the magma can only go up (least compressed direction). The volcano appears over the point of least compression, which can be either a cinder cone field or a stratovolcano (or group of stratovolcanoes) dependent on the time span between eruptions & the warmth of the crust.

2:) an intermediate magma chamber: this develops when a long fracture set squeezes in from the base of the crust periodically over a long time interval forming a stratovolcano over one or more megathrust cycles. The intermediate magma chamber is the result of residual magma held in the conduit for a long time interval in between the bubbling through of gas from repeated small inputs of magma from the fracture set. The magma chamber develops as a result of recompression from the crust squeezing the magma in the base of the conduit upward between the primary magma ingress events, with the base of the conduit becoming warm & flat, and the upper pert of the conduit becoming filled to bursting point with degassed magma. On occasion the upper part of the magma chamber is squeezed out as a dome or flow on the surface. The bulk of the magma in the intermediate chamber is a subvertical stock between 40 & 20km depth.

3:) A high level magma chamber is the final development in a volcano where the compression of an intermediate level magma chamber squeezes the magma upward and then sideways in a sill complex beneath the stratovolcano or complex of stratovolcanoes on the surface. This is usually grown as a multi stage result of pods of magma from numerous generations of intermediate level magma chambers. Spectacular caldera forming eruptions tend to result from a large gas rich magma filled fracture squeezing into the base of such a chamber (Krakatau, Tambora, Crater Lake etc.

4:) & just to be annoying, a deep sill of gas rich magma may occasionally develop & base crustal depths in the arc part of a backarc basin which may inflate to hundreds of km3 by the input of numerous fracture sets of gas rich magma. The result is the catastrophic partial melting of the crust above the sill, with development of a stock of dacite magma which evolves to rhyolite as it melts & is squeezed through the crust. The result of the magma reaching the surface is a relatively large low relief caldera. The continued "squeeze box" effect of arc tectonics is the further squeezing of the degassed parts of the pluton to high levels with further caldera forming eruptions as a result of ingress if gas rich magma from the fracture set. A nest of low relief calderas results from this situation, typical examples being Kikai, Kurile lake, Taupo, & Okataina.

This article appears to describe an intermediate level magma chamber.

have a nice day: Ag
Max MBA

San Jose, CA

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#2
Feb 19, 2014
 

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Once again limey, PLEASE STOP SPAMMING OUR HOMETOWN FORUM! Everything we need to know about the Earth can be found in the Holy Bible.

There are absolutely no volcanics in Solano County, California so, nobody here gives a damn.

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

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#3
Feb 24, 2014
 
Max MBA wrote:
Once again limey, PLEASE STOP SPAMMING OUR HOMETOWN FORUM! Everything we need to know about the Earth can be found in the Holy Bible.
There are absolutely no volcanics in Solano County, California so, nobody here gives a damn.
Ah I finally see.

You are one of the new age religious recidivists whom believe the world is flat & that everyone whom is not a religious recidivist should go back to slavery in the plantations.

Do you believe the world is flat 7 the sun revolves around it? apparently 1.4 of americans believe that to be the case.

As far as I can tell this thread has nothing to do with Solano county. Is it dry over there yet?

Have a nice day: Ag

Since: Aug 10

Citrus Heights, CA

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#4
Mar 5, 2014
 

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Adrian Godsafe MSc wrote:
<quoted text>
Ah I finally see.
You are one of the new age religious recidivists whom believe the world is flat & that everyone whom is not a religious recidivist should go back to slavery in the plantations.
Do you believe the world is flat 7 the sun revolves around it? apparently 1.4 of americans believe that to be the case.
As far as I can tell this thread has nothing to do with Solano county. Is it dry over there yet?
Have a nice day: Ag
Sadly, I too heard about the survey of high schoolers where over 50% believe that the sun revolves around the earth. Why wouldn't they? They worship a president who believes the entire universe revolves around him.

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