Thermal evolution of the Crater Lake of Copahue Volcano with ASTER during the last quiescence period between 2000 and 2012 eruptions

Abstract

Active Crater Lakes are the surface expression of volcanic activity at the top of complex magmatic-hydrothermal systems. The Volcanic and Hydrothermal System Copahue is one of the most important active systems in Argentina. It lies at the border of Argentina and Chile and is very important, since the Copahue and Caviahue towns are very close and constitute important touristic resources including a ski center. The aim of this work is to improve the temperature register of the volcano and contribute towards a better understanding of the thermal behavior of the system during the quiescence period between the 2000 and 2012 eruptions. The surface temperature of the Crater Lake was estimated by using the Normalized Emissivity Method (NEM) on 70 images acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and we combined them with field measurements in order to capture the fundamental variations of the system. The analysis allowed the identification of two different thermal periods: (i) January 2001–August 2003 and (ii) December 2004–November 2011, characterized by temperature ranges of 43–50 °C and 30–45 °C, respectively. Beyond these ranges, temperature anomalies or moments of high temperature variability occurred, which corresponded to surface expressions of volcanic activity. In August 2004, the lake froze almost completely, whereas in March 2012, peak temperatures were recorded. However, a significant drop in temperature prior to the eruption of December 22, 2012, was observed, which might constitute a characteristic feature of the system. Furthermore, the Crater Lake of Copahue volcano is classified as a lake of high activity. The observations and interpretations presented constitute a useful baseline and a significant contribution towards a better understanding of the functioning of the volcano, the mitigation of volcanic hazards and the identification of volcanic unrest.