Rock glaciers climatic and dynamic monitoring in the subtropical Andes of northwestern Argentina.

MARTINI, MATEO; FLORES, ELISEO

Dublin

Congreso; INQUA; 2019

International Union for Quaternary Research (INQUA)

The subtropical Andes of northwestern Argentina have ranges that reach more than 6000 m a.s.l. At high-altitudes, arid and cold conditions prevail, and rock glaciers are one of the most widespread features. Active rock glaciers exist above 4500 m a.s.l. where precipitation is less than 500 mm/yr. In this contribution we present the results of the geomorphological mapping, and climatic and dynamic monitoring of two active rock glaciers: the Varasrock glacier (VRG) and Lizoite rock glacier (LRG).We used differential GPS to accurately measure the position of a network of boulders once a year to stablish the rock glaciers superficial flow. In order to know the climatic conditions affectingboth rock glaciers, we installed a weather station on their surface to record hourly air and soil temperature, global solar radiation and relative humidity.The VRGis situated above 4500 m a.s.l (23° 12' 9.12"S, 65° 3' 43.31"W) in the Cordillera Oriental. Based on the position, it is classified as a talus-derived rock glacier, indicating a periglacial origin. A network of 24 boulders was monitored every year between 2012 and 2016 using a differential GPS. During the entire period of measurement, the VRGregistered movements between 125 and 5 cm/yr, except for four boulders which did not move. Over the five years of monitoring, the mean annual air temperature remained above 0 ºC (between 2.6 and 3.5 ºC), and only for four months the mean temperature was negative. Mean annual temperatures at 5 and 50 cm depth range between 4.7-6.1 and 4.6-5.0, respectively. The LRG is located in a glacial cirque in the Sierra de Santa Victoria of the Cordillera Oriental (22°11'41.70"S, 65°11'29.95"W). It is located above 4552 m a.s.l. and presents morphological characteristics that denote activity.Two years of thermal monitoring show positive air and soiltemperature. The mean annual air temperature rangesbetween 3.1-4.1ºC; the soil temperatureat 5 cm depth ranges between 5.8-7.2ºC; and the soil temperature at 50 cm ranges between 5-6.1ºC. The superficial flow of the rock glacier, based on the measurement of 20 boulders, ranges from 3.5 to 14.7 cm/yr. In the front of the glacier there is a small lake, from which sediment cores were taken for paleoclimatic studies.Both rock glaciers are under positive air temperatures and bellow the regional 0º C isotherm altitude (5000 m a.s.l.). 106 years of temperature instrumental record located at La Quiaca station (3459 m a.s.l.) reveals a warming trend of 0.8 ºC during the last century. Therefore, it is possible that the Cordillera Oriental rock glaciers (i.e., VRG and LRG) are not in equilibrium or fully adapted to the current climatic conditions.