sgr ms thesis - University of Maine

The potential for volcanic eruption is dependent on the critical rate of reservoir
pressurization by magma replenishment. If the rate of reservoir pressurization is
lower than the critical level defined by the visco-elastic strength of the wall rock,
volume expansion is accommodated by viscous deformation and magma is
stored in the reservoir. Magma storage is controlled by a viscous regime. If the
rate of pressure increase exceeds the critical level, the reservoir walls are
compromised by elastic failure, a conduit forms (Barnett and Lorig, 2007), and
volcanic eruption commences. Volcanic eruption is controlled by an elastic
regime (Jellinek and DePaolo, 2003, Scandura et al., 2007, 2008).
Much like viscous regime magma reservoir growth, elastic regime volcanic
eruption is controlled by the mechanical behavior of the reservoir walls. There
are two possible end-member responses depedent on the rigidity of wall rock: the
“elastic reservoir”, where elastic energy stored in a non-rigid wall rock is
immediately released by the formation of a conduit to the surface, and the “rigid
reservoir model”, where the elastic strength of rigid wall rock is surpassed by
pressure changes in the reservoir, leading to brecciation (Wadge, 1981;
Scandone, 1996). Elastic, non-rigid behavior of wall rock can be seen in some
basaltic eruptions where there is a rapid and effusive initial peak in magma
discharge that slowly reduces over time (Figure 3.2). Rigid reservoir behavior is
reflected in felsic eruptions, where magma cannot be “squeezed out” elastically,
but as a conduit forms to the surface, pressure release in the chamber causes
volatiles to volumetrically expand, leading to explosive eruption. Peak magma
discharge occurs later on, when a conduit is well developed and the abundant
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