The Unidad Estatal de Protección Civil de Colima reported that on 26 September seismicity at Colima increased, and crater incandescence was observed later that day. On 27 September small landslides originating from a new and growing lava dome traveled 100 m down the S flank. The exclusion zone was increased from 5 to 10 km in the Montegrande canyon; a 5-km exclusion zone was maintained in the other areas. According to news articles, incandescent landslides traveled down the S and SE flanks during 29 September-1 October. Gas-and-ash plumes rose 4 km and caused ashfall in nearby areas including La Becererra, La Yerbabuena, San Antonio, and El Jabali in the municipality of Comala, Montitlán in the municipality of Cuauhtémoc, and Juan Barragan in Tonila, Jalisco. On 1 October the Colima State government stated that the communities of La Yerbabuena (80 people) and La Becerrera (230 people) were preemptively evacuated, and the exclusion zone was extended to 12 km except on the Jalisco side (maintained at 7.5 km). A news article noted that Juan Barragan was also evacuated.

The Washington VAAC reported that on 29 September gas-and-steam emission possibly containing minor amounts of ash rose to an altitude of 4.9 km (16,000 ft) a.s.l. and drifted NW. On 30 September the webcam showed intense activity and crater incandescence, and gas-and-steam emissions that may have contained ash drifting WNW. An intense thermal anomaly was visible in short-wave infrared satellite images. Later that day an ash plume rose to an altitude of 5.8 km (19,000 ft) a.s.l. and drifted 35 km W. Possible emissions with ash were recorded by the webcam on 1 October; weather clouds obscured views of the crater. An ash plume detected in satellite images drifted almost 40 km S and SW. Later that day the webcam recorded explosions and pyroclastic flows. On 2 October ash plumes rose to altitudes of 6.1-8.2 km (20,000-27,000 ft) a.s.l. and drifted SW and W. Emissions later that day were mostly comprised of gas and steam; seismicity decreased, though a thermal anomaly continued to be detected in satellite images. On 3 October ash plumes rose to altitudes of 5.5-6.4 km (18,000-21,000 ft) a.s.l. and drifted 25-40 km SW and SWW. Ashfall was reported in areas on the S and SW flanks. Based on webcam views ash emissions rose to an estimated altitude of 5.5 km (18,000 ft) a.s.l. and drifted S on 4 October.

Geological Summary. The Colima complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the high point of the complex) on the north and the historically active Volcán de Colima at the south. A group of late-Pleistocene cinder cones is located on the floor of the Colima graben west and east of the complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide scarp, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, producing thick debris-avalanche deposits on three sides of the complex. Frequent recorded eruptions date back to the 16th century. Occasional major explosive eruptions have destroyed the summit (most recently in 1913) and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Sources: Unidad Estatal de Protección Civil de Colima, Washington Volcanic Ash Advisory Center (VAAC), Televisa