Under Active Volcanoes, Magma Sits in...

Under Active Volcanoes, Magma Sits in Cold Storage

There are 7 comments on the Live Science story from Feb 16, 2014, titled Under Active Volcanoes, Magma Sits in Cold Storage. In it, Live Science reports that:

Strike that iconic image of a tall, snow-capped volcano sitting atop a liquid pool of hot, molten magma.

Join the discussion below, or Read more at Live Science.

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#1 Feb 17, 2014
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

Martinez, CA

#2 Feb 17, 2014
WTF does this have to do with the City of Vacaville?

This is the VACAVILLE FORUM on TOPIX, not the Rocks & Minerals self-help group.
A Thought

Vacaville, CA

#3 Feb 17, 2014
Max wrote:
WTF does this have to do with the City of Vacaville?
This is the VACAVILLE FORUM on TOPIX, not the Rocks & Minerals self-help group.
Ya' kind of have to admit, things have been a bit boring here in Vacaville lately. We need a good controversy to stir things up......
Belleview Resident

Vallejo, CA

#4 Feb 18, 2014
A Thought wrote:
<quoted text>
Ya' kind of have to admit, things have been a bit boring here in Vacaville lately. We need a good controversy to stir things up......
Magma is a great controversy!
Max

Union City, CA

#5 Feb 18, 2014
Belleview Resident wrote:
<quoted text>
Magma is a great controversy!
Just like the scientific frauds of evolution, global climate change and autism, "cold magma" does NOT exist. It's not even a theory.

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#6 Feb 19, 2014
Max wrote:
<quoted text>Just like the scientific frauds of evolution, global climate change and autism, "cold magma" does NOT exist. It's not even a theory.
Cold magma does exist.

Also known as Granite.

In some cases sills of rapidly chilled granite intruded into flat lying shales (Granophyre) may still contain bubbles of exsolved gas (this occurs in Wales (UK).

A granite rapidly chilled during an eruption often shows rings of K & Na feldspar with interesting circular snowball accumulations (very popular in bank frontages). This type of granite (Rapakivi granite) was effectively solid after the eruption but was hot & gassy enough to recrystallize the alternating Na & K rich snowball bands into crystals large enough to see. The rest of the granite forming the matrix between the snowballs was initially pumice before being squished down & recrystallized. The result (see bank frontages) was very pretty to look at when cut & polished, with enough surface weathering to colour up the K feldspar into a pink or red colour as a result of Ce replacing some of the K and weathering to Ce2O3.

Have a nice day: Ag
Max

Alamo, CA

#7 Feb 19, 2014
Adrian Godsafe MSc wrote:
<quoted text>
Cold magma does exist.
Also known as Granite.
In some cases sills of rapidly chilled granite intruded into flat lying shales (Granophyre) may still contain bubbles of exsolved gas (this occurs in Wales (UK).
A granite rapidly chilled during an eruption often shows rings of K & Na feldspar with interesting circular snowball accumulations (very popular in bank frontages). This type of granite (Rapakivi granite) was effectively solid after the eruption but was hot & gassy enough to recrystallize the alternating Na & K rich snowball bands into crystals large enough to see. The rest of the granite forming the matrix between the snowballs was initially pumice before being squished down & recrystallized. The result (see bank frontages) was very pretty to look at when cut & polished, with enough surface weathering to colour up the K feldspar into a pink or red colour as a result of Ce replacing some of the K and weathering to Ce2O3.
Have a nice day: Ag
Well, if it doesn't happen within the confines of Solano County, we're not interested. Go and SPAM another forum with your useless trivia.

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