Increased soil temperature detected at Machín volcano, Colombia

The Colombian Geological Service (SGC) found changes in vegetation and increased soil temperature during their inspection of the Cerro Machín volcano. The last eruption at this volcano took place in 1180 CE ± 150 years.

SGC carried out an inspection on February 18, 2023, at Finca La Florida, close to the Cerro Machín volcano, due to the reported changes in vegetation and a possible increase in soil temperature.

Located 300 meters (984 feet) above the La Florida thermal spring, which recorded a temperature of approximately 79 °C (174.2 °F) during the last geochemical sampling in September 2022, the inspection observed temperature values ranging from 70 to 95 °C (158 to 203 °F), a pulsatile steam outlet, and vegetation with a dry and burned appearance. Despite the changes, no odors were detected.¹

These surface manifestations are typical of active volcanoes with changes in their behavior, denoting the VCM’s yellow level. To monitor these changes and determine their potential origin, the SGC will conduct more detailed sampling in the area.

Seismicity under the Cerro Machín volcano began increasing at 11:23 LT on December 2, 2022, with signals indicating rock fracturing. By 13:20 LT, 393 signals were detected, with the largest event recorded at M4.5 at 12:36 LT. The earthquake occurred 900 m (2 900 feet) SSW of the main dome at a depth of 3 km (1.8 miles) and was felt in Cajamarca (14 km / 8.7 miles WSW), Ibagué (17 km / 10.5 miles ESE), and in other municipalities of Tolima.²

The last eruption of this small but explosive volcano, located at the southern end of the Ruiz-Tolima massif, took place in 1180 CE ± 150 years. Since then, the volcano has experienced several instances of increased seismic activity, most notably in 2008, when approximately 400 – 450 people evacuated to shelters or other safe areas due to 1 210 volcano-tectonic earthquakes recorded from November 8 to 10.

Geological summary

The small Cerro Machín stratovolcano lies at the southern end of the Ruiz-Tolima massif about 20 km (12.4 miles) WNW of the city of Ibagué.

A 3 km (1.8 miles) wide caldera is breached to the south and contains three forested dacitic lava domes. Voluminous pyroclastic flows traveled up to 40 km (24.8 miles). away during eruptions in the mid-to-late Holocene, perhaps associated with the 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.³

References:

¹ Posibles cambios de temperatura del suelo en el volcán Cerro Machín – SGC – February 28, 2023

² Increased seismicity under Machín volcano, Colombia – The Watchers – December 8, 2023

³ Machín – Geological summary – GVP

Featured image credit: Machin volcano on February 2, 2023. Credit: Copernicus EU/Sentinel-2, The Watchers

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