The Servicio Geologico Colombiano (SGC) reported increased activity and gas-and-ash emissions at Puracé. Continuous volcanic tremor was recorded by the seismic network during 19-25 November. Seismic signals indicting rock fracturing occurred at similar levels compared to the week before with events located between the Puracé, Piocollo, and Curiquinga volcanoes at depths of 1-3 km. Sulfur dioxide emissions remained within the range recorded in previous weeks. Slow deformation between the Puracé, Piocollo, and Curiquinga volcanoes had continued since the eruptive episode at Curiquinga on 20 January. On 23 November the characteristics of seismic signals indicating fluid movement changed, with some signals accompanied by ash emissions identified by the monitoring network and observed by surrounding communities and SCG employees conducting fieldwork. The earthquakes were mainly located beneath the W flank at depths less than 1 km. At 0638 on 25 November a gas-and-ash plume rose 1.6 km above the summit and drifted SW. On 27 November ashfall was reported in various locations NW in the municipality of Puracé, specifically in rural areas including Cristales, Anambío (7 km NW), Alto Michabala, and Chapío, and to the W in the municipal seat of Coconuco (11 km WNW). Minor ashfall and strong sulfur odors during 0800-1000 on 29 November were reported by residents of the Río Negro village in the Paletará district (16 km SW), from the Mina de Azufre, Agua Hirviendo (10 km WNW), and Totoró road areas, and the N part of Popayán (28 km NW). Activity intensified during the morning of 30 November. The seismic network detected an increase in both the intensity and number of earthquakes associated with fluid movement. Several ash-and-gas plumes were observed rising as high as 1 km above the summit and drifting NW. At 0830 the Alert Level was raised to Orange (the second highest level on a four-color scale) and the public was warned to stay away from the crater. Unidad Nacional para la Gestión del Riesgo de Desastres (UNGRD) recommended that local authorities consider evacuating about 70 residents living in a high-threat sector.

On 1 December a resident of Pululó village (about 7 km SW) noted that the color of the San Francisco River had changed color and had a brown hue, possibly related to rain transporting ash into the river. Ashfall was noted in San Juan de Puracé area at around 1400. Later that day, at 2327 a tremor signal was associated with a gas-and-ash plume that rose 500 m above the summit and drifted SE. During 1-2 December seismicity remained elevated and was associated with continuous gas-and-steam emissions that drifted in various directions. Some of the emissions contained ash and rose around 500 m above the summit, though weather conditions sometimes obscured views.

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.

Sources: Servicio Geológico Colombiano (SGC), Gestión del Riesgo de Desastres (UNGRD), Gobernación del Cauca