Thermal simulations on periglacial soils of the Central Andes, Argentina

Abstract

Rock glaciers are the most common landforms of the Andean periglacial landscape in the Central Andes of San Juan, Argentina. Their active layer is gravelly with a typical openwork structure. The upper parts of these rock glaciers are coarse-grained Turbic Cryosols, with no vegetation cover. Since March 2018, coarse soils in the active layer of the “Candidato” rock glacier have been monitored (31.9°S, 70.18°W). Three trenches, 4,000 m a.s.l. and down to a depth of 90 cm, were equipped with sensors to measure soil temperature and volumetric water content. We also measured particle size distributions and calculated thermal properties from soil samples. The mean thermal conductivities for unfrozen and frozen soils were 0.69 and 0.54 W m−1 K−1, respectively, and the mean thermal diffusivities were 2.05 × 10−7 and 1.64 × 10–7 m2 s−1, respectively. Analysis of the seasonal thermal and hydrological fluxes in the active layer is challenging, as the physical properties change cyclically, thus controlling processes such as water storage, infiltration and seepage, heat balance, mechanical behavior, and kinematic response. We used the Coupled Heat and Mass Transfer Model for the Soil–Plant–Atmosphere System (COUP) numerical computerized model, performing a site-specific calibration, to simulate soil temperatures, active layer thicknesses, and seasonal freezing–thawing depths. The model implemented, in combination with a reanalysis of the meteorological data series, performed very well to reproduce the data from thermo-sensors placed in the ground. This proposed methodology is viable for areas with limited instrumentation or low accessibility. The “Candidato” rock glacier can be used as a pilot model for thermal modeling purposes on rhyolitic rock glaciers in the region.