Evolution of the Late Holocene landslide-dammed Laguna Blanca, Subtropical Andes of Argentina (31°S)

Abstract

The Laguna Blanca (31◦52′S; 69◦59′W), located in the Subtropical Andes of Argentina, is an example of a lake naturally dammed by a large rock avalanche formed ~12.8 ka ago in a high-mountain narrow valley. Two lake levels were identified, providing evidence of at least two palaeoshorelines. The older lake level could not be directly dated. The second level gradually filled, with oscillating lake margins, between ~2.5 ka and 2.1 ka based on luminescence ages presented here. Sedimentological and magnetic properties analyses were conducted in the second palaeolacustrine sequence to reconstruct lake level fluctuations during the palaeolake existence and infer post-drainage palaeoclimatic conditions in reference to regional records. According to our results, the second palaeolake partially drained sometime after 2.1 ka, exposing a short section (<2 m). Nevertheless, the bottom section could still be underwater, while the top was mobilized by the wind. Wetter climatic conditions were inferred post-partial drainage within this semi-arid setting, promoting subtle eluviation processes recognized through magnetic minerals and sedimentological analysis. Subsequently, the aeolian dunes signify drier conditions that last until today, coinciding with regional palaeoclimatic records.