Mechanisms for rainfall-concurrent lava dome collapses at Soufriere Hills Volcano, 2000-2002

The evolution of rainfall-concurrent dome collapses at Soufrière Hills volcano is followed using a limit equilibrium model for rain infiltration into a hot lava carapace. Magma infusing into the dome both supplies heat and builds the slopes. The dome rocks are cooled by episodic rain infiltration and climatic cooling. Rainfall infiltrates fractures that develop in the hot dome carapace, occludes the void space, and staunches effusive gas flow. Gases may originate from juvenile de-gassing of the dome interior, or result from the vaporization of infiltrating water. Gas pressures build in cracks blocked-off by rain, and may destabilize the dome. The effects of dome growth, heating by magma infusion, and cooling by rain infiltration and climatic influences, are combined to follow the growth of the dome towards ultimate collapse. For a fixed suite of strength and transport parameters, and for measured magma influx rates, the evolution of instability may be followed. The evolving factor of safety tracks the observed March 2000 and July 2001 rainfall-concurrent collapse events, which evolve over months. However, the resolution of the hindcast is unable to discriminate between the effects of closely-timed rainfall events (order of hours). The heightening of the dome is shown to exert the principal influence on average slopes and in the evolution of instability. Collapse removes the over-heightened dome, and temporarily restores stability.