IANIGLA   20881
Unidad Ejecutora - UE
congresos y reuniones científicas
Permafrost detection through the use of geophysical methods in the Blanco River Basin, San Juan, Argentina
Congreso; XI. International Conference On Permafrost; 2016
Geophysical prospection is an indirect method which aims to determine the presence, depth and geometry of the base and top of the permafrost, in particular, for mountain areas where the permafrost pattern is often very complex (Vonder Mühll et al., 2001; Hausmann et al., 2007). It is an important technique that can also aid to establish the degree of activity of the rock glaciers.In this work, we describe geophysical surveys in five rock glaciers which have been conducted in the Santa Cruz River and Frio River watersheds located in the south west of San Juan province, which are part of Blanco river basin along the Central Andes of Argentina. This watershed has a total area of 4,860 sq. km and a large number of periglacial environment landforms (about 1000, among active and inactive rock glaciers and protalus).We conducted between 7 to 3 geophysical 2-D surveys in five rock glaciers (El Colorado, El Negro, El Amarillo, El Pelado and Los Patos Norte) when the active layer shows greater development (March - April). We used 2-D seismic tomography in longitudinal and transverse traces. We estimated rock glacier activity based on satellite imagery. And we registered Vertical Electrical Sounding (VES) in two of the five rock glaciers.We found that El Colorado rock glacier has a permafrost thickness of 14 m, with sectors up to 18 m thickness and mean p-wave velocity of 2500 m/s. VES performed on the central area of this body showed an active layer?s depth of 2.67 m (142 Ω m resistivity) and permafrost thickness of 8.39 m (23.6 KΩ m resistivity).El Negro rock glacier has an active layer with an average thickness of 3 m and mean p-wave velocity of 500 m/s. In particular, El Negro rock glacier permafrost has an average thickness of 7 m with local thickness up to 20 m and mean p-wave velocity of 2500 m/s.El Amarillo rock glacier has an active layer with an average thickness of 1.5 to 5 m, with mean p-wave value of about 600 m/s. The greatest thicknesses coincide with collapse structures. Permafrost thickness is about 15 m, with sectors of up to 35 m in thickness with p-wave velocities vary between 1000 and 2800 m/s (Figure N° 1).Los Patos Norte rock glacier has an average active layer thickness of 2 m and p-wave velocity of about 400 m/s. Permafrost average thickness is about 10 m with sectors of up to 20 m thick. Average p-wave velocity is about 2800 m/s.In El Negro rock glacier our results are consistent with the ones measured by Arenson et al (2010). In addition we found that El Negro rock glacier also has termokarst features, which indicates certain disequilibrium with the current climatic conditions.We also found signs of permafrost degradation inferred from seismic profile at the front slope in El Amarillo rock glacier.We found that El Pelado rock glacier is inactive, that is consistent with morphological analysis.REFERENCESArenson LU, Pastore S, Trombotto D, Bolling S, Quiroz MA, Ochoa X. 2010. Characteristics of two Rock Glaciers in the Dry Argentinean Andes based on Initial Surface Investigations. GEO 2010, Calgary, Alberta.Hausmann H, Krainer K, Brückl E and Mostler W. 2007. Internal Structure and Ice Content of Reichenkar Rock Glacier (Stubai Alps, Austria) Assessed by Geophysical Investigations. Permafrost and Periglac. Process. 18: 351?367 (2007) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ppp.601Vonder Mühll D, Hauck C, Gubler H, McDonald R and Russill N. 2001. New Geophysical Methods of Investigating the Nature and Distribution of Mountain Permafrost with Special Reference to Radiometry Techniques. Permafrost and Periglacial Processes. Process. 12: 27?38. DOI: 10.1002/ppp.382.