Avances in the periglacial hydrology of the Stepanek rock glacier, Andes Centrales, Mendoza, Argentina

CRISTINA DAPEÑA; DARIO TROMBOTTO LIAUDAT; NOELIA SILEO

Wellington

Simposio; The Cryosphere in a Changing Climate; 2017

Sponsored by the International Glaciological Society (IGS), the International Association of Cryospheric Sciences (IACS), and the Climate and Cryosphere (CliC) project.

In the región of the Stepanek rock glacier (approximately 69º19´ / 69º26´ W and 32º 55´ / 32º 59´ S), Cordón del Plata, Mendoza, Argentina a continuous hydrochemical monitoring is being done. The aim is to analyze underground and superficial waters which interact with the cryoform. The cryogenic basin of the study area where the hydrological flows are originated is of 6,5 km2 and is interrupted by the mentioned cryoform, as in other cases of the Dry and Central Andes. This cryoform is a rock glacier of glacigenic origin. The origin of the water may be snow, rain or graupel depending on the height and was interpreted according to the isotopic studies. Excesses of deuterium supported this argument. The water proceeds from the melting of perennial and temporary snow patches and from the melting of the active layer which is frozen in winter. This situation does not only apply to this rock glacier but also to entire the upper basin of the valley. The active layer is in partly saturated with winter precipitation which is related to storms from the Atlantic as well as from the Pacific Ocean. Supposedly, and according to the analysis of the isotopic enrichment of a sample of 2013, superficial water or groundwater is becoming a water supply from the intrapermafrost of the cryoform, because of degrading and melting permafrost (Sileo et al., 2015). This process may be supported by the scenery of the global warming or climatic variability. The hydrogeochemical research allows the interpretation of different water flows, which cross the rock glacier through its active layer. This water flow is suprapermafrost water, but it is supposed that other flows may use a subpermafrost way. Two different monitoring sites Van06 (3479 m asl) and Vmn07 (front of the cryoform, 3338 m asl), 800 m of distance between one another, show interesting anomalies with a descent of their temperature of 2.4 °C, parallel to altitude descending but a rise of the pH from 2 to 3 units. In the same way there is a notable reduction in the concentration of some heavy metals, which are first detected at the monitoring point Van06. They may be considered health threatening like Cd (average 2013-2015 = 0,023±0,002 mg/L), Zn2+ (average 2013-2015 = 4,2±0,4 mg/L) y Ni (average 2013-2015 = 0,928±0,093 mg/L). This anomaly allows to infer a retention of chemical elements in the internal structure of the rock glacier, although it is not clear yet, using tracers, which way this flow is using when it crosses the cryoform. The concentration of Si, measured in Van07, also shows a decreasing in superficial water and that also substantiatives the idea that Si may also be retained in the internal structure of the cryoform. This last topic was also remarked before by Trombotto (see 1985 and 1991).