Cross-Section Guide

• This is a schematic cross section of Mount St. Helens, plotting earthquake locations and their relation to structures in the plumbing system of Mount St. Helens inferred from seismology, petrology and GPS studies. The main features of the plumbing system are:
• A magma chamber that extends from 6 km to approximately 15 km below the 1980 crater floor. The magma chamber has gotten larger and smaller through time, as new batches of magma have been intruded and erupted. This is depicted by the dotted lines above the deep magma chamber.<\LI>
• A smaller chamber at approximately 2 km below the 1980 crater floor.
• A widening of the conduit above 1 km depth.
• The new dome is located at the top of the conduit and is shown by a red mass next to the 1980-1986 dome.