Evidence of rock-wall permafrost in the “Portillo Argentino” crossing (Dry-Central Andes of Argentina)

TAPIA, CARLA; CASTRO, MARIANO; PECKER MARCOSIG IVANNA

Whitehorse

Congreso; ICOP 2024; 2024

In high mountains, the air temperature and solar radiation control the likelihood of rock-wall permafrost occurrence. Due to the low ice content, which is primarily confined to discontinuities and joints within the rock massif, the thermal response to an external shift is usually quick. Permafrost occurrence in rock-walls affects the geomechanical response of rock massifs, by reducing the resistance of the frozen rocks and joints once the 0 °C threshold is surpassed.The "Portillo Argentino" is a narrow mountain pass, located above 4300 m asl between the Tunuyán and Tupungato valleys in Argentina (33°37’ S and 69°36’ W) (Figure 1). During the warm season it is used by riders and hikers, as it has historical, environmental, and esthetical significance.Annually, the thawing season with monthly mean air temperatures > 0 °C extends from November to April, while the freezing season starts in May to December. The precipitation patterns show a well-defined seasonal regime, with maximum precipitation during the cold season and scarce precipitation during the warm season. Precipitation is nival, with annual means ranging from 200 to 300 mm during the dry “La Niña” phases. The mean annual air temperature (MAAT) at approximately 3950 m asl (Piuquenes Automatic weather station – AWS – years 2019 to 2022) is of -0.93 °C; during the thawing season MAAT ascends up to 9.11 °C, descending down to -16.88 °C during the cold season. In the Piuquenes valley, the ice bodies are distributed altitudinally in a range that varies between 3200 and 5900 m asl, with an average height of 4500 m asl. According to the modeling provided by (Tapia-Baldis & Trombotto-Liaudat, 2020), there is a high probability of finding permafrost in the rock-wall outcrops above 4000 m asl (Figure 1). Nevertheless, this hyphotesis has never been tested before in the area. Rock glaciers are located in the lowest altitude range up to approximately 5000 masl, while glaciers and perennial snow patches from 3800 to 5900 m asl. Approximately 65% of the glaciers face south, southeast and east, coinciding with the coldest slope in the southern hemisphere and the main direction of runoff.Since January 2022, eight temperature data loggers (iButtons ® DS1922L) were installed above 4100 m asl inside the rock outcrops, to verify the presence or absence of rock-wall permafrost (Figure 2). The temperature data in boreholes of 18 mm diameter, between 10-20 cm depth, covering different topographic orientations (Figure 2c). Temperature measurements are recorded every 4 hours and were first retrieved in March 2023.