A cross-section showing shallow and deep aquifer tops from the nort...

Data show that there are two aquifers at Mount St. Helens, with the upper extents indicated by the blue lines. The shallow aquifer (solid blue line) is fed by Crater Glacier and heated by hot rock beneath the 2004-08 dome. The deeper, regional aquifer (dashed blue line) mounds up slightly beneath the volcano and deepens beneath the Pumice Plain. The solid black line is the ground surface.

CSAMT sounding data were supplemented by water-table data from wells and 11 lakes and 11 springs in the area.