Outburst flood deposit in the source of the Arroyo Turbio, Domuyo Volcano, Northpatagonian Andes (Argentina).

HURLEY, MARÍA; COLAVITTO, BRUNO; FOLGUERA, ANDRÉS

Concepción

Congreso; XV CONGRESO GEOLÓGICO CHILENO; 2018

Universidad de Concepción

The Arroyo Turbio drains the north face of the Domuyo Volcano, in the Northern Patagonian Andes in the province of Neuquén. A wide floodplain dominates the valley from 36°33´18?S to 36°34´07?S. It is partially composed of large blocks that may imply mass wasting processes ocurrence previously overlooked. Its thickness increases up to 5 meters in some sectors. It is inverse gradedand poorly selected with sharp to slightly rounded blocks with diameters of >3 m. Clasts correspond mostly to sedimentary rocks provenant from Mesozoic deposits of the Neuquén basin that crop out along the valley walls, as a result of the Domuyo basement uplift. Quotes from an inhabitant of the zone described the deposit as a product of a catastrophic process generated by the dambreach that drained a lake causing a flood downstream and damaging inhabited areas. Unfortunately, due to the low population existent in the area, there are not historical records that could address for the potential age of the success. We study the deposit using satellite images. It extends downstream in the proximal segment of the Arroyo Turbio. It has a total area of 224.000 m2which assuming an average thickness of 3 m allows us estimating an approximate volume of 0.67 x106 m3 . Upstream the deposit, the valley gets narrower and exhibits in its western side incisions that can be result of the stream erosion potential. We propose that the flow started from a frontal moraine observed 2.6 km downstream the glacier. At its proximities it is possible to identify apotential paleolake level, from which we estimated an area for the ancient water body of 0.1 km2 . Following these considerations, the deposit could be interpreted as a Glacial Lake Outburst Flood (GLOF), due to the sudden drainage of a glacial lake triggered by moraine failure. From its dimensions, it can be compared to the one described in Estero El Pedregoso Lake, where a lake areaprevious to the unload of 0.12 km2 and an outburst volume of 0.28 x106 m3 were estimated (GLOF data from Iribarren Anacona et al. (2014)). These processes are frequent in high mountain regions susceptible to climate changes. The Andes of Chubut and Río Negro present historical records of these processes (e.g. Colavitto et al. 2012, Worni et al. 2012). In the Andes of Neuquén there is yet no record of this type of events, hence this preliminary study aims to be a trigger for future research.