Abstract
A slope collapse in a narrow, mountainous valley led to the formation of a latest-Pleistocene (14,500 cal. BP) lake dammed behind this mass-movement deposit in the Betic Cordillera (SE Spain). The lithostructural conditions of the carbonate bedrock, a warm and more humid period at the end of the last glaciation (Bølling interstadial), and its location very close to a seismic mountain front provide the ideal context for the destabilization and failure of bedrock and the subsequent formation of this ephemeral mountain basin. It was filled in 260 years. Estimated specific sediment yield (SSY) is at least two orders lower than SSY nowadays in SE Spain. The calculated value of 81 t/km 2/y is similar to calculated values from artificial reservoirs in more humid and temperate drainage areas, such as in Central Europe. Geomorphological and sedimentological features of the siltation of the landslide-dammed reservoir have been preserved close to the Betic Cordillera mountain front. The reservoir fill consists of over 30 m of lacustrine and alluvial deposits. The lake created upstream of the landslide dam was silted by mainly terrigenous (Gilbert-type delta gravels and turbiditic sands) and mixed terrigenous–bioclastic sedimentation (horizontally laminated carbonate mudstones). After the lake was silted, a meandering river caused linear erosion over the natural dam and deeply dissected the lacustrine deposits above the river’s pre-landslide profile. This process has allowed the study of the well-preserved internal structure of the natural reservoir and identification of the stages in the construction and degradation of a semi-closed basin. The stages involved in the evolution of the landslide-dammed reservoir may provide insights into studying the development of other closed or semi-closed basins such as mountain basins or artificial dams.
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