Erosional and depositional features produced by a convulsive event,San Carlos,Colombia, September 21, 1990

The upper catchment, of the San Carlos River, located on the eastern slope of the Colombian Central Cordillera, was affected by a rainstorm which had no historic equivalent in the area, caused 20 deaths and important destruction and therefore might be called convulsive in the sense of Clifton (1988). Steep upper slopes suffered more than one hundred shallow mudflows. In the catchment channel deepening and widening cut through older torrential and slope deposits and weathered granodiorite, A large amount of material was eroded including blocks up to 8 m in diameter. Resultings deposits show the well-known differentiation: blocks accumulated in the upper part, coarse and settled in the intermediate course and clay was carried to the Punchinà Reservois about 20 km downstream. A volcanic ash layer which covers the older torrential deposits shows mineral assemblages which may enable its correlation with other ashes found eastward with an age estimated in about 10.500 years BP.