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

MATEO MARTINI; ELISEO FLORES

Dublin

Congreso; INQUA Congress 2019; 2019

International Union for Quaternary Research (INQUA)

The subtropical Andesof northwestern Argentina have ranges that reach more than 6000 m a.s.l. Athigh-altitudes, arid and cold conditions prevail, and rock glaciers are one ofthe 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 theresults of the geomorphological mapping, and climatic and dynamic monitoring oftwo active rock glaciers: the Varas rock glacier (VRG) and Lizoite rock glacier(LRG).We used differentialGPS to accurately measure the position of a network of boulders once a year tostablish the rock glaciers superficial flow. In order to know the climaticconditions affecting both rock glaciers, we installed a weather station ontheir surface to record hourly air and soil temperature, global solar radiationand relative humidity.The VRG is situatedabove 4500 m a.s.l (23° 12' 9.12"S, 65° 3' 43.31"W) in the CordilleraOriental. Based on the position, it is classified as a talus-derived rockglacier, indicating a periglacial origin. A network of 24 boulders wasmonitored every year between 2012 and 2016 using a differential GPS. During theentire period of measurement, the VRG registered movements between 125 and 5cm/yr, except for four boulders which did not move. Over the five years ofmonitoring, the mean annual air temperature remained above 0 ºC (between 2.6 and3.5 ºC), and only for four months the mean temperature was negative. Meanannual temperatures at 5 and 50 cm depth range between 4.7-6.1 and 4.6-5.0,respectively.The LRG is located ina 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 presentsmorphological characteristics that denote activity. Two years of thermalmonitoring show positive air and soil temperature. The mean annual airtemperature ranges between 3.1-4.1ºC; the soil temperature at 5 cm depth rangesbetween 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 20boulders, ranges from 3.5 to 14.7 cm/yr. In the front of the glacier there is asmall lake, from which sediment cores were taken for paleoclimatic studies.Both rock glaciers areunder positive air temperatures and bellow the regional 0º C isotherm altitude(5000 m a.s.l.). 106 years of temperature instrumental record located at LaQuiaca station (3459 m a.s.l.) reveals a warming trend of 0.8 ºC during thelast century. Therefore, it is possible that the Cordillera Oriental rockglaciers (i.e., VRG and LRG) are not in equilibrium or fully adapted to thecurrent climatic conditions.