Servicio Geológico Colombiano (SGC) reported that a seismic swarm below Cerro Negro de Mayasquer and Chiles volcanoes began at 0100 on 3 December. The events were classified as volcano-tectonic, with epicenters located up to 6 km from the summit of Chiles volcano, at depths of less than 8 km (4.7 km a.s.l.). The maximum local magnitude was 2.3. From the beginning of the swarm until the time of the report posting (1640) there were about 5,400 recorded events, making the swarm the largest since 2015. The report also noted that seismicity had gradually been increasing in recent weeks. The Alert Level remained at Yellow (level 2 of 4).

Geological Summary. The Chiles-Cerro Negro volcanic complex includes both the Pleistocene Chiles and the Cerro Negro de Mayasquer stratovolcanoes astride the Colombia-Ecuador border. Cerro Negro has a caldera open to the west, with andesitic and dacitic lava flows of possible Holocene age (Hall 1992, pers. comm.) and solfataras on the shore of a small crater lake. An eruption reported in 1936 may have been from Reventador (Catalog of Active Volcanoes of the World). The higher, glacier-covered summit of Chiles, about 4 km ESE of Cerro Negro, last erupted about 160,000 years ago, but it has a caldera open to the north with hot springs and an active hydrothermal system on its eastern flank.

Source: Servicio Geológico Colombiano (SGC)