Eruptive and magma circulation patterns determined by satellite imagery: The case of Lascar volcano, Northern Chile

Abstract:

Lascar volcano (23°22’ S; 67°44’ W; 5.592 m a.s.l.) is located in northern Chile, 70 km SE from San Pedro de Atacama, and is considered as the most active volcano in Central Volcanic Zone. Its activity is characterized by a permanent emission of a gas plume, occasionally interrupted by vulcanian eruptions, and less frequently by sub-plinian eruptions. Qualitative and quantitative analysis of thermal anomaly variations detected in its active crater using Landsat TM and ETM+ images, combined with ground-based measurements, has allowed us to establish an eruptive pattern and relate it to magma circulation. Low intensity eruptions are related to degassing pathways obstruction induced by partial collapse of inner walls of active crater, which produce a decreasing of gas released to atmosphere and consequently an increasing of internal pressure in the magmatic system by volatile accumulation. In this case, low intensity thermal anomalies are detected, with heat flux of 75-765 MW. At critical pressures, energy is liberated as vulcanian eruptions, with columns no higher than 8 km altitude, releasing exclusively non-juvenile products (e.g. July 2000, December 2003 eruptions). After low intensity eruptions, thermal anomalies and heat flux values increase reaching up to 1,005-10,527 MW. On the other hand, high intensity eruptions seems to be related to influx of new and high temperature magma in a cold and more evolved magma chamber, which induce to eruptive processes characterized by emission of columns higher than 15 km altitude and production of pyroclastic flows by column collapse (e.g. April 1993 sub-plinian eruption). Despite previous to high intensity eruptions thermal anomalies and heat flux decrease, during high intensity eruptions heat flux can reach up 867,000 MW, returning subsequently to lower flux values (~10,000 MW).