Climatic and geomorphological controls of rock glaciers in the Andes of Central Chile

Rock glaciers are ubiquitous landforms in the dry Andes, and significant, but unheralded stores of frozen water. In this study, statistical modelling techniques and geomorphological mapping are applied to quantify and analyze the distribution of rock glaciers in the Andes of Central Chile (27–35◦ S) as related to climate and topography. Special emphasis is put on the the Andes of Santiago (33–34.5◦ S). A statistical sample survey and a logistic regression model were designed to quantitatively estimate distribution patterns and characterize the geomorphological niche of rock glaciers based upon digital elevation models. These methods proved to be efficient instruments that are complementary to field mapping and remote-sensing techniques. The amount of water stored within rock glaciers of the Andes of Santiago per unit area is by one order of magnitude higher than in the Swiss Alps, reaching an average 0.7–1.1 km3 of water equivalent per 1000 km2 in the Andes. At least one fifth of the high-mountain area of the Andes of Santiago drains through intact rock glaciers. This statistical estimate underlines the importance of rock glaciers within the Andean hydrological and debris-transport system. On a local scale, the optimal rock glacier niche in the Andes of Santiago is characterized by a convergent contributing area of 0.5–1 km2 and modern mean annual air temperatures of +1 to −1◦C, corresponding to 3500–3800 m a. s. l. Sporadic intact rock glaciers reach down to 3000 m a. s. l. at places with favorable morphography and topoclimate including low incoming solar radiation. Huge rock glaciers of more than 1.5 km2 are in contrast favored by north-facing glacier-free cirques at higher elevations. They are among the largest known rock glaciers on Earth. The overall distribution pattern of rock glaciers in Central Chile is influenced by precipitation, past and modern glaciation, topography and volcanism. These act as combined controls at the northern (27◦ S) and southern (35◦ S) limit of rock glacier occurrence in the Chilean area of winter precipitation. Rock glacier sediment budgets revealing Holocene denudation rates, and the use of rock glaciers as permafrost indicators give further insight into the periglacial environment of the Andes of Central Chile.

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