Rock Glacier Response to Climate Change in the Argentinian Andes

DREWES J.; KORUP O.; MOREIRAS S.M.

Simposio; AGU meeting; 2017

Rock glaciers are bodies of frozen debris and ice that move under the influence of gravity in permafrost areas. Rock glaciers may store a large amount of sediments and play an important role as prime movers of debris in the Andean sediment cascade. However, little is known about how much sediment and water rock glaciers may store at the mountain-belt scale, and the few existing estimates vary considerably. We address this question for the Argentinian Andes, for which a new glacial inventory containing more than 6500 rock glaciers gives us the opportunity to analyse their relevance within the sediment cascade.We examine the inventory for catchments in five sub-regions, i.e. the Desert Andes (22°?31°S); the Central Andes (31°?36°S); the Northern Andes of Patagonia (36°?45°S); the Southern Andes of Patagonia (45°?52°S); and Tierra del Fuego (52°?55°S), together with climate variables of the WorldClim datasets, and digital topographic data, to estimate how rock-glacier extents may change under different past and future climate scenarios.We observe for the northern Desert Andes that rock glacier toes are at 4000 to 5000 m a.s.l. and a mean annual temperature range of 3° and 8°C, though most rock glaciers are in areas with mean annual temperatures between ?5 and 5°C, marking a distinct thermal niche. Rock glaciers are traditionally viewed as diagnostic of sporadic alpine permafrost and their toes are often near the annual mean 0°C isotherm. However, we find that only rock glaciers in the southern Desert Andes and Central Andes are located where annual mean temperature is ?2°C. Future scenarios project an increase of > four degrees in these areas, which may further degrade ground ice and potentially change the rates at which rock glaciers advance. Where active rock glaciers become inactive their coarse material, which was formerly bound by ice, may be released into the sediment cascade, whereas accelerating or rapidly downwasting rock glaciers may either interfere with river systems or release episodic debris flows. Hence, understanding the role of rock glaciers sediment and water storage will help to estimate and locate future areas susceptible to catastrophic sediment releases.