Combined thermal and seismic analysis of the Villarrica volcano lava lake, Chile

Abstract

Villarrica volcano, a 2,850 m basaltic-andesite stratocone in southern Chile ((39°25' S-71°42' W), has had an active summit lava lake (30-60 m diameter) since the last eruption in 1984-85. Current activity is characterised by mild strombolian activity, continuous degassing, and periodic larger explosions. Between August-December 1999, Villarrica showed a significant increase in seismic activity. Lava lake activity increased and larger discrete explosions occurred destroying the lava lake crust on, at least, 4 occasions. Since February 1999, radiance data provided by the NOAA GOES 8 satellite via the University of Hawaii hot spot monitoring web-site served, as an additional real time monitoring method of the lava lake. Preliminary GOES data, for the period February-December 1999, have been correlated with seismic RSAM data and visual observations. Correlations exist between these data sets only for the most active periods. At Villarrica, the small dimensional and temporal exposure of the lava lake surface and the narrow crater coupled with a low satellite viewing angle generate a very subtle hot spot signature. Radiance variations can only provide reliable data where adequate constraining ground information exists and viewing conditions are optimal. However, the hot spot tool, once refined is considered a potentially important method of improving the monitoring capabilities.