XXX Magma Chamber deep under Merapi?
Given the recent attention and interest of the Merapi volcano in Indonesia that has been erupting since 26-Oct-2010, it may be of interest to discover some of the details of its magma chamber.
In fact, there apparently is not just one magma chamber underneath Merapi, but quite likely two chambers, one of them possibly being triple size XXX the volume of the other.
A shallow magma chamber is approximately located between 1.5 km and 2.5 km beneath the surface. This is the magma chamber that has delivered most of the eruptive materials during most of its eruptive history.
The average size explosive eruption has been a VEI 2, meaning the magma chamber is probably in the vicinity of 10 million cubic meters (the total amount typically ejected during a VEI 2 eruption).
However, it may be that a larger and deeper magma chamber is feeding the upper shallow chamber.
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A study by Francois Beauducel from the Department of Seismology of the Institut de Physique du Globe de Paris, reveals that there is a larger deep magma chamber located 8.9 km beneath the surface whose chamber may be three times the total volume of the one above it.
The findings are derived from GPS displacements and tilt observations.
A magma conduit channel measuring 20 meters in diameter extends from the chamber to about 1 km beneath the Merapi summit.
A illustration from the study depicts some of the reasoning.
A PDF of the study can be downloaded here.
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The Merapi volcano first started erupting during October 26, 2010. The eruption has been the largest there in 100 years.
Unfortunately more than 150 people have lost their lives by pyroclastic flows and ash, as it continues. The volcanic ash has reached altitudes of 40 to 50 thousand feet causing restricted air travel and cancellations, while several hundred thousand people have been evacuated nearby.
Surely this ash will travel the globe, having reached into the stratosphere. The question is, how long will it go on and how bad will it get.
The Merapi volcano is one of the most active volcanoes in the world, regularly produces pyroclastic flows, it has been active for 10 thousand years, and is considered to be very dangerous.
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Do you mean another chamber with a diameter three times that of the smaller chamber or with a volume three times the volume of the smaller chamber? It does not take a very large increase in diameter to produce three times the volume. Your diagram is visually consistent with three times the diameter. If the first one is one K diameter that means it hold 4/3pi cubic K of magma (about 4) but if the second one is 3K diameter that means it holds 36picubic kilometers about 108
@numbercruncher, Excellent observation. The study suggests that the lower magma chamber to be 3x the total volume of the upper, and therefore the original drawing was disproportionate. Having worked through the numbers, volume=4/3*pi*radius^3, if upper chamber holds 10 million cubic meters (VEI-2 explosivity index), the diameter (if a sphere) would be 268 meters. A chamber holding 30 million cubic meters would have a diameter of 386 meters (1.4 times that of the other). The image has now been adjusted to better reflect this. Thanks for pointing it out ;=)