Magnetotellurics and Mt. St. Helens in New Scientist

MT used to look at magma under Mt. St. Helens:

"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 travelling 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."


Link: http://www.newscientist.com/article/mg20227124.700-supervolcano-may-be-brewing-beneath-mount-st-helens.html