The highly fractured area on the right side of this 3 May 1980 photo is the renowned N-flank "bulge" of Mount St. Helens. Intense deformation producing northward displacements up to 2.5 m per day and reduction of rock strength by hydrothermal alteration caused the catastrophic collapse of the N flank, triggering the devastating magmatic explosive eruptions of 18 May.

Photo by William Melson, 1980 (Smithsonian Institution).

Keywords: crater | cryptodome | ash | deposit

St. Helens