According to INGEOMINAS, Observatory Vulcanológico and Sismológico de Manizales reported a period of increased seismicity from Cerro Machín on 31 December. A total of 346 volcano-tectonic events no stronger than M 2.1 were located S and SW of the main lava dome. On 1 January seismicity again increased, and at the time of the report, 367 events had been detected. The low-magnitude events were located S and SW of the main dome at depths between 2.5 and 4.5 km. The largest event, M 2.3, was located S of the dome at a depth of about 3.3 km and felt by residents near the volcano and in the municipality of Cajamarca, 14 km WSW. 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)