PERMAFROST-VOLCANO INTERACTIONS: A CASE-STUDY IN DECEPTION ISLAND

GOYANES, G.; VIEIRA, G.; CASELLI, A.; CARDOSO, M.; MARMY, A.; BERNARDO, I.; HAUCK, C.

Portland

Congreso; XXXII SCAR and Open Science Conference & COMNAP XXIV AGM; 2012

SCAR and Portland State University

   Deception Island is a strato-volcano located in Bransfield Strait (Maritime Antarctica) with recent eruptions in 1842, 1912, 1917, 1967, 1969 and 1970. In this work the main focus is at an alluvial fan dominated by debris-flow processes located behind the Argentinean Base ?Decepción?. It is one of the areas with ground geothermal anomalies. Surface temperatures have been measured in summer 2010-2011 with a hand digital thermometer at 5, 50 and 70 cm depth. Miniature dataloggers were installed at 5, 10, 20, 40 and 80 cm depth at two sites in the alluvial fan. Air temperature dataloggers were installed at 1.5 m. Thaw depth was measured with a probe. Nine geoelectrical profiles were carried out.    Data shows that the temperatures increase with depth near the lagoon. Maximum values are found near to the lagoon where permafrost is absent and, in proximal alluvial fan and in the debris cones, temperatures reach minimum values. Here, the probe confirmed permafrost presence at approximately 70 cm depth.    The shallow borehole located in proximal alluvial fan shows a good agreement between air and subsurface temperature and it also supports permafrost presence. On the contrary, the borehole at the distal site shows a thermal stratification all year-round and only the first 20 cm show a response to air temperature. The lowest sensor reached temperatures of 12 ºC.    The electrical resistivity tomographies point two distinct zones: (1) the distal alluvial fan, where the resistivities are low, excluding the presence of ice and (2) the proximal alluvial fan and debris cones where the high resistivities show the presence of permafrost.    Profiles of resistivity also evidence the presence of a conductive wedge of marine water corresponding to the lagoon that penetrates under the alluvial fan with hot water. Due to its high temperature, it inhibits permafrost development, although the air temperature descends under 0ºC. But, water temperature and the borehole located at proximal alluvial fan show that the effect of thermal anomaly is extremely restrict to a narrow area near to the beach. In the electrical resistivity tomographies the transition between conductive and resistive zones is very abrupt, also indicating the local character of the thermal anomaly. For this, results show that the thermal anomaly controls the permafrost distribution.