Observatory Vulcanológico and Sismológico de Manizales reported a seismic crisis at Cerro Machín on 24 July, characterized by volcano-tectonic earthquakes. One of the earthquakes was a M 2.6, located S of the main lava dome at a depth of 3.96 km. The next day a M 4.1 volcano-tectonic earthquake occurred 0.8 km S of the main dome at a depth of 3.88 km. On 29 July the number of volcano-tectonic events increased; the earthquakes were a maximum M 1.73 and between 3 and 4 km depth, S of the main dome. The Alert level remained at III (Yellow; "changes in the behavior of volcanic activity").

Geological Summary. The small Cerro Machín stratovolcano lies at the southern end of the Ruiz-Tolima massif about 20 km WNW of the city of Ibagué. A 3-km-wide caldera is breached to the south and contains three forested dacitic lava domes. Voluminous pyroclastic flows traveled up to 40 km away during eruptions in the mid-to-late Holocene, perhaps associated with formation of the caldera. Late-Holocene eruptions produced dacitic block-and-ash flows that traveled through the breach in the caldera rim to the west and south. The latest known eruption of took place about 800 years ago.

Source: Servicio Geológico Colombiano (SGC)