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Indy
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Yellowstone 'Melt'
I was looking around at information about Yellowstone and I find this on the USGS site...
| Quote From Source: | How large is the magma chamber that is currently under Yellowstone? How much magma is there under Yellowstone?
The term magma chamber is commonly thought to be an area of 100% melted rock. However, scientists have found that nearly all magma bodies contain a mixture of solid and melted rock (geologists call the mixture a partial-melt). One way to think about a magma chamber or magma body is to picture a water-filled sponge. The sponge would represent the solid rock whereas the water would represent the melt. Beneath Yellowstone, on average, the magma is about 90% solid rock (like a hot sponge) containing 10% liquid rock in its pores. Some regions may have higher melt fractions, and some may contain lower melt fractions.
Geophysical studies cause us to conclude that the Yellowstone magma body is shaped like a banana lying on its side with ends pointing up - it has a volume of approximately 15,000 cubic km. This irregular-shaped body extends beneath the caldera and is about 60 km long NE-SW and up to 40 km wide. The magma body is closest to the surface near its ends where the top of the body is about 5-6 km deep and bottom of the body is about 16 km deep. The two volcanic resurgent domes at Yellowstone are near to the areas where the magma body is closest to the surface.
The size, shape, location, and composition of the magma body is determined by seismic studies called seismic tomography. Medical CAT scans, which bounce X-rays through the human body to make three-dimensional pictures of internal tissue, are a similar diagnostic technique. Seismic tomography uses seismograms from thousands of local earthquakes to measure the speed of sound waves through the earth. Geophysicists compare the velocity of the sound waves at Yellowstone to the faster waves moving through normal cold rock. From these comparisons the geophysicists can create 3-D images of structures deep in the Earth, and infer the composition of the structures. A decrease in velocity from the average value can be interpreted to be a hot, melt-rich volume. Given the pressure, temperature, and uncertainties in their models, the scientists estimate that the melt part could be about 10% of the low velocity volume or about 1,500-2,000 cubic km. It's important to understand that this tomographic technique gives a very coarse look at the subsurface. We are averaging data over many kilometer-sized distances so that we cannot look at small (< 1 km) regions of the subsurface.
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Source: http://volcanoes.usgs.gov/yvo/faqsscience.html#fast
It is the 'melt' that is the eruptable stuff. So there is far more than enough melt down there for one massive eruption. The only thing that we don't know is where this stuff is at.
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posted on 5/28/2007 at 20:49
