IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Geomorphological Map of a Post Glacial-Periglacial Landscape: Bramadero River Basin (Central Andes, Argentina).
Autor/es:
KAZUYUKI SAITO; KAZUYUKI SAITO; DARIO TROMBOTTO LIAUDAT; DARIO TROMBOTTO LIAUDAT; CARLA TAPIA BALDIS; CARLA TAPIA BALDIS
Lugar:
Sapporo
Reunión:
Conferencia; 2nd Asian Conference on Permafrost (ACOP2017; 2017
Institución organizadora:
International Permafrost Association
Resumen:
This work presents a detailed geomorphological map of a relatively little studied region in the Central Andes of Argentina. Here, we combine geomorphological and geocryological investigations in the post-glacial landscapes in the Bramadero river valley(located in the homonymous basin)in the Central Andes of Argentina in order to reconstruct the relationship between glacial and periglacial phenomena, as well, as to outline a chronological model of their evolution. Final map presented at 1.10.000 scale indicates the presence and extension of geoforms and geomorphological process above an area of 250 km2 and is the result of a detailed interpretation based on imagery from different sensors and data extraction using digital elevation models. Bramadero river valley is located in the Central Andes of SW San Juan (Argentina) at 31° 50´ S and 70° 00? W. Weather conditions in the region show a well-defined seasonal regime with maximum precipitation (300-400mm/yr) during the cold season(April-October) and scarce precipitation during warm season(November-March).A weather station placed on the bottom of main valley recorded a MAAT(Mean Annual Air Temperature)of -2.15 °C between 2009-2014 at a height of 4019 m asl. Based on the digital analysis of high-resolution images five groups of geoforms were discriminated according to or phogenetic criteria: 1) glacial geoforms and related deposits;2) periglacial geoforms; 3) mass wasting deposits; 4) alluvial and fluvial geoforms and 5) polygenetic geoforms. Extraction of topographic parameters from a digital elevation model also allowed the quantification of topographic determinants for each one of them. Only 34% of the total surface (ca. 87 km2) is occupied by bedrock, while 66% (167 km2) exhibits geoforms resulting from active processes. Rock glaciers are the conspicuous cryoforms in the landscape and the most representative form of creeping permafrost together with protalus lobes and protalus ramparts; other periglacial cryoforms include cryoplains and frozen talus slopes. Igneous bedrock outcrops are widespreadon the west and middle sides of the basin while towards the eastside, sedimentary bedrock is exposed. Soli-and gelifluction, debris flows, snow-debris avalanches among other mass wasting processes, fluvial erosion, nivation and deflation are the most common processes on the upper slopes. These, supply the lower slopes with coarse-grained and block-sized sediment that accumulates on different geoforms that aggrade below free bedrock surfaces(debris cones, non-vegetated alluvial fans, protalus forms and rock glaciers in different stages of development) resulting in a highly active system in continuous evolution under periglacial present conditions. Bramadero river basin was largely glaciated during the last glaciation, even today it is possible to recognize erosive forms and glacial deposits all over the main valley and subordinated creeks. Remnants glaciers bodies (glaciers and debris covered glaciers)only cover up to 2% of basin surface (ca. 0.8 km2)above 4300 m asl, while Holocene glacial deposits occupy 11.5% of the basin (ca. 30 km2),and can be found downstream up to ca. 2700 masl. Currently, periglacial processes are active in elevations exceeding 2700 m asl (lowest limit of seasonal freezing), however, a wide variety of periglacial deposits and permafrost indicators cryoforms occurs between 3500 and >4500 m asl (permafrost periglacial belt) (Tapia & Trombotto 2015). Concluding, Bramadero river valley exhibits evidence of past periods with enhanced glacial and periglacial activity. The degree of post-glacial periglacial landscape transformation is likely linked to climatic trends as well to geological and hydrological settings.References:Tapia Baldis, C. & Trombotto, D. 2015. Cryogenic altitudinal belts in Bramadero river basin, San Juan, Argentina. Acta Geológica Lilloana, 27(2): 146-158 (in Spanish)