Abstract

New cosmogenic nuclide exposure ages of rock-avalanche deposits in front of Sierra Laguna Blanca in the arid Argentine Puna Plateau demonstrate the effects of westward propagation of reverse faulting and the influence of active faulting on slope oversteepening and subsequent gravitational collapse. The 21Ne exposure ages of 8 superposed landslides with volumes >0.3 km3 are between ca. 150 and 430 ka, and indicate an average recurrence interval of large gravitational mountain-front failures of ∼27.5 k.y. for the ultimate 7 landslides. Landsliding did not occur after 150 ka along this sector of the Sierra Laguna Blanca. The termination of landsliding activity correlates with reverse-fault propagation into the piedmont area of the Sierra Laguna Blanca. The exposure age of ca. 130 ka of a tectonically uplifted terrace postdates initiation of fault activity in the piedmont region, and the fault scarp height of 120 m indicates important continued uplift in the piedmont; no further offsets occurred at the mountain front. Due to this lack of tectonic activity at the mountain front, no further collapse has occurred, indicating that in this environment catastrophic mountain-front failure is mainly controlled by tectonically driven slope oversteepening.

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