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A climatic trigger for catastrophic Pleistocene-Holocene debris flows in the Eastern Andean Cordillera of Colombia

Abstract:

The geomorphology and stratigraphy of massive debris flows on the Eastern Andean Cordillera, Colombia, indicate two distinct deposits can be recognized. The lower Chinauta deposit covers 14 km2 and has a thickness of ~60m, whereas the upper Fusagasugá deposit covers 20 km2 and has a thickness of ~20m. The lower Chinauta section consists of matrix-supported gravels, with isolated boulders and massive to moderately bedded structure and local inverse grading. The upper section displays sequences of inversely graded, clast-supported gravels, with boulders >2m in axial length, capped by massive, matrix-supported fine gravels. The latter are dissected by coarse, channelized gravels. We interpret these facies as a series of debris and hyper-concentrated flows dissected by river channels. The Fusagasugá deposit is dominated by massive to inversely graded matrix-supported gravels with isolated boulders. Single-grain, optically stimulated luminescence dates of the sandy-silty matrix of debris and hyper-concentrated flows constrain the timing of deposition of the Chinauta debris flow deposits between 38.9 and 8.7ka. We postulate that millennial-scale climate variability is responsible for causing these massive debris flows, through a combination of elevated temperatures and increased rainfall that triggered runoff and sediment transport.