TRACKING LAVA LAKE FLUCTUATIONS AT VILLARRICA VOLCANO, CHILE

Fluctuations in the level (±80m) of the lava lake of Villarrica Volcano, Chile occur regularly. The lava lake fluctuates in height with cycles of gradual build up over months followed by sudden withdrawal. Filling and draining of magma in the lake reflects dynamic behavior in the lower conduit and magma chamber. In the system, magma is thought to convect freely with escaping volatiles playing an important driving role. Two possible scenarios exist when magma-free surface reaches the crater rim: overflow onto the flanks, or flank fissuring and draining of the conduit. Each has fundamentally different hazard implications. Height fluctuations of lava lakes are considered common, yet surprisingly virtually no quantitative information on this exists. Data will be extracted from thermal data from Geostationary Operational Environmental Satellite (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellites, photographic archives and summit observations since 1984. Temperature data for each lava lake pixel in successive images will be extracted to generate temperature variations over time. This will shed light on the physical processes controlling the behavior of the lava lake by providing information on the temporal scale of the fluctuations over the last 23 yrs. A preliminary analysis of GOES data for 1999 illustrated good agreement between thermal and seismic data when the magma free surface was <90 m below the crater rim. This limit was determined by viewing constraints of the satellite. Combining the height and thermal data will support the correct ‘Hot Spot' alert level being established for Villarrica Volcano.