This work presents some geophysical results obtained at Mesón San Juan located in the Central Andes (6,012 m, 33°30' Sand 69°49' W), on the border of Argentina and Chile. The permafrost plateau (4,400 m) situated at the loot of the glacier is limited by recent moraines produced by cryogenic phenomena. The geophysical results revealed lateral differences in the dielectric characteristics of the subsurface due to varying water contents, allowing a zoning of the permafrost structure. We have compared the electrical permittivities in a semi-quantitative way through a trial-and-error migration procedure, taking advantage of the clutter present in the permafrost as seen in the fixed-offset data. In this way we were able to recognize a confined zone of relatively low phase velocity indicating higher porosity and water content. We interpret that zone as degraded permafrost , probably a result of the impact of global warming on the Andean cryolithozone. That zone is likely a discharge channel linking a suprapermafrost to a subpermafrost aquifer, part of a laterally discontinuous near surface system not mapped in this work.
degraded permafrost; GPR imaging; global warming; Andes
