UNGRD

In: Hermelín A., Michel, ed. Memorias. Medellín, Antioquia. Universidad EAFIT, jul. 1992. v.1. v.1. Presentado en: Simposio Latinoamericano de Riesgo Geológico Urbano, 2; Conferencia Colombiana de Geología Ambiental, 2; Pereira, 15-18 jul. 1992. The upper catchment of the San Carlos River (Antioquia, Colombia)contains several levels of old torrential deposits Which overlie saprolite derived from the Antioquian Batholite granodiorite. Around Calderas Hydrielectric Plant, which was partially destroyed by a convulsive event on Septembrer 2lst, 1990, four levels were observed: Betulia 3 (B3), the oldest; Betulia 2 (B2), Betulia 2A (B2A)and Arenosa 1 (A1), the youngest. Each one of this levels was formed by a single deposit, excepting Betulia 2 which contains two. The older torrential deposits are covered by Quaternary andesitic ashes erupted in the Ruíz-Tolima Massif, located 100 km soutward. Four volcanic units were identified: a mixed unit containing volcanic minerals (UD)overlying Arenosa 1; another mixed unit (UVD)covering Betulia 2A; an anphibole-hypersthene volcanic unit (UV2)overlying Betulia 2 and Betulia 3, also identified in a neightbouring Calderas alluvial terrace; and a amphibole unit (UV1)encoutered only in the Calderas terrace. Units UV1 and UV2 may tentatively be correlated with Unidad Superior (10.000 BP)and Unidad Volcanic Intermedia (20.000 BP)respectively, which were defined in a preliminary tephrastratigraphic classification made in the Antioquia highlands located west of the study area. This correlation permits the inference that at least similar torrential events (Arenosa 1 and Betulia 2A)ocurred during the last 10.000 years in the catchment; three more torrential events (Betulia 3 and two compresed in Betulia 2)happened between 10.000 and 20.000 years BP (AU). / ANTIOQUIA