The Impact of Ice Sheet Withdrawal on the Stability of Magma Systems

Abstract:

Monitoring the activity of volcanoes along the Aleutian Arc in Alaska is important to the safety of local populations, as well as air traffic flying through the region. However, observations of volcanic unrest are limited by accessibility and resources, particularly at glacier-covered systems making investigations of their stability challenging. Westdahl Peak, a glacially covered volcano on Unimak Island in the Aleutian Arc has experienced significant unrest and uplift since its explosive, VEI 3 eruption in 1991-1992. Given the magnitude of observed uplift, previous investigations suggested the potential eruption by 2010 (e.g., Lu et al. 2004), but no such event has occurred. In this study, thermomechanical finite element models are used to evaluate how magma system stability at a glaciated volcano is impacted by variations in ice sheet thickness, magma chamber depth, and magma flux rate. The generic ice sheet model is then applied to investigate the current unrest and stability of the Westdahl system. Our numerical experiments indicate that presence of an ice sheet increases the average repose interval for a magma system. For a spherical magma chamber located 5 km deep, ice sheet thicknesses of 1 km, 2 km, or 3 km increase repose intervals about 8%, 16%, and 25% respectively. However, for deeper magma chambers (> 5 km), the increase in the repose interval was diminished. Additionally, the percent increase in repose interval is not impacted by variations in magma flux rate for a given ice sheet thickness and magma chamber geometry. The numerical estimates further suggest that the ice sheet on Westdahl Peak, which is ~ 1 km, may have only a minimal impact, minorly increasing the stability of the magma system. In general, given flux rates and magma chamber geometries estimated for the Westdahl system, the repose interval is estimated to be increased by 0.3 years due to the Westdahl glacier. In conclusion, numerical models indicate that ice sheets may increase repose intervals for shallow magma systems, improving their stability in glaciated regions such as the Aleutians, Iceland, and Antarctica.