A Quantitative Analysis of a Non-Eruptive Volcanic Event: Mt. Spurr, Alaska, 2002-2006

Mt. Spurr is a volcano in proximity to Anchorage, Alaska and major airline routes making an eruption or episode of unrest potentially hazardous. Between 2004 and 2006, Mt. Spurr underwent such an episode of unrest involving increased seismic activity, CO2 emissions, ice melting, and debris flows, which was likely forecasted by the increased seismicity of Oct 2002. The timeline of events provide data to construct a model analyzing the thermal energy release and constraining subsurface magmatic and hydrothermal processes during the period of unrest. The results show that the ice cauldron formation and the increase of meltwater temperature could not have been caused by the observed CO2 release alone and suggest that enhanced hydrothermal heat transfer related to increased CO2 output could provide the thermal power necessary to drive the melting event. Scaling hydrothermal convection in terms of its Rayleigh number and using boundary layer analysis suggests that the mean permeability of the volcanic edifice prior to the unrest event was ~10-14 m2. CO2 release, most likely related to mechanical fracturing of the edifice by over-pressurized fluids at depth and signaled by increased seismicity likely enhanced the hydrothermal Rayleigh number and heat output by a combination of heating and increased permeability.