We've discussed the supervolcano beneath Yellowstone a few times here (not going to blow, 2004; going to blow, 2008). Now scientists are pondering whether a large area of conductive material beneath Mt. St. Helens might contain enough magma that the area could be classed a supervolcano. The jury is still out on this one. Reader nhytefall sends us a New Scientist progress report. "Magma can be detected with a technique called magnetotellurics, which builds up a picture of what lies underground by measuring fluctuations in electric and magnetic fields at the surface. The fields fluctuate in response to electric currents traveling below the surface, induced by lightning storms and other phenomena. The currents are stronger when magma is present, since it is a better conductor than solid rock. ... [M]easurements revealed a column of conductive material that extends downward from the volcano. About 15 km below the surface, the relatively narrow column appears to connect to a much bigger zone of conductive material. This larger zone was first identified in the 1980s by another magnetotelluric survey, and was found to extend all the way to beneath Mount Rainier 70 km to the north-east, and Mount Adams 50 km to the east. It was thought to be a zone of wet sediment, water being a good electrical conductor. ... [Some researchers] now think the conductive material is more likely to be a semi-molten mixture. Its conductivity is not high enough for it to be pure magma.. so it is more likely to be a mixture of solid and molten rock."
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