Puracé has been seismically monitored since 1989; during February-April 2000 some anomalous seismicity occurred. First, on 2 February a MR 4.7 tectonic earthquake and some volcano-tectonic (VT) earthquakes struck with epicenters near the town of Paispamba almost 15 km SW of the volcano. Next, a swarm consisting of 32 earthquakes occurred with M 0.0 to M 1.5; these events took place during 2-3 February; depths were at 7-9 km, and their magnitudes were over 1.5. Subsequently they migrated to the SE, ending on 21-22 April with 53 earthquakes in a cluster located 4.5 km NE of the volcano at depths of 2.5-8 km. A synopsis of the epicenter data appears in figure 1.

Figure 1. Epicenters determined for seismic events at Puracé during February to April 2000. The figure also shows the locations of the six telemetered seismic receivers. Courtesy of Observatorio Vulcanológico y Sismológico de Popayán (INGEOMINAS).

Geological Summary. Puracé is an active andesitic volcano with a 600-m-diameter summit crater at the NW end of the Los Coconucos Volcanic Chain. This volcanic complex includes nine composite and five monogenetic volcanoes, extending from the Puracé crater more than 6 km SE to the summit of Pan de Azúcar stratovolcano. The dacitic massif which the complex is built on extends about 13 km NW-SE and 10 km NE-SW. Frequent small to moderate explosive eruptions reported since 1816 CE have modified the morphology of the summit crater, with the largest eruptions in 1849, 1869, and 1885.

Information Contacts: Fabiola Rodríguez and Jaime Raigosa, Observatorio Vulcanológico y Sismológico de Popayán, INGEOMINAS, Popayán, Colombia; Hector Cepeda, INGEOMINAS, Bogotá, Colombia.