Debris flows triggered from melt of seasonal snow and ice within the active layer in the semi-arid Andes

Debris flows triggered from rapid melt of seasonal snow, and/or ice within the active layer have not been studied in periglacial areas of the semi-arid Andes. Therefore, through a representative watershed we investigated the thermo-radiative characteristics, possible water sources, and current and future frequency of these debris flows. Information was collected on three temporal clusters of debris flows during which no rains or major earthquakes occurred. The thermo-radiative conditions of each cluster were analyzed through nearby stations that cover the entire watershed altitudinal range. Snow cover was calculated using the closest satellite images before and after each cluster in order to evaluate the potential contribution of snowmelt for each. The frequency of melting-driven debris flows, for the remainder of the 21st century, was evaluated by calculating the trends of climatic variables that control them. The results indicate that debris flows show several patterns such as: a lag of several hours between the warmest hours of the day and their triggering, occurrence in clusters of 3-5 days during the early summer, and an accelerated increase in temperature over the days previous to the beginning of the clusters. In addition, it was inferred that the water of debris flows can come from the melt of seasonal snow as well as of shallow ice within the active layer. Lastly, due to a positive trend of maximum air temperature of the warmest trimester and high inter-annual variability of precipitation, a frequency increase is likely, followed by a possible decrease due to the negative and positive trends of precipitation and mean air temperature, respectively.