Figure 5
From: Causes of volcanic unrest at Mt. Spurr in 2004–2005 inferred from repeated tomography
Conceptual scheme of the possible stages of the Mt. Spurr volcanic activity. (A) Magmatic eruption in 1992 via the flank conduit. No activity occurred in the summit area, which was screened by a non-permeable self-sealed zone (SSL) depicted by the gray layer. (B) Relaxation period from 1996 to 2001: the flank conduit becomes impassable. Fluids (blue dots) accumulate in the ductile part of the magma reservoir. (C) Beginning of the unrest from 2002 to 2004; the strong seismic activity without apparent degassing on the surface represents disruption of the SSL and penetration of liquid fluids into the brittle part of the crust (blue arrows and lines). (D) Volcanic unrest from 2004 to 2006; liquid fluids reach the phase separation level and then continue ascending as gas (white arrows and lines).
