St. Helens might be part of a supervolcano.
IS A supervolcano brewing beneath Mount St Helens? Peering under the volcano has revealed what may be an extraordinarily large zone of semi-molten rock, which would be capable of feeding a giant eruption.
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.
Graham Hill of GNS Science, an earth and nuclear science institute in Wellington, New Zealand, led a team that set up magnetotelluric sensors around Mount St Helens in Washington state, which erupted with force in 1980. The measurements revealed a column of conductive material that extends downward from the volcano. About 15 kilometres below the surface, the relatively narrow column appears to connect to a much bigger zone of conductive material.
I remember when St. Helens blew in 1980; besides all the general noise, for months afterward every time the thing hiccupped- or seemed about to- the voice on the Civil Defense phone would put out a warning. Assuming it actually is one part of a supervolcano base, if it ever blew for real there'd probably be one warning- "Ok, folks, we're all screwed"- and that's it.