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Earthquake swarm in the vicinity of El Chichon volcano, Mexico

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Mexico's National Seismological Service (SSN) has registered a total of 22 earthquakes within 35 km (22 miles) of El Chichon (El Chichonal) volcano from December 24, 2020, to January 19, 2021. The last eruption of this volcano took place in 1982 (VEI 5). More than 10 large explosive eruptions have occurred there since the mid-Holocene. 

The quakes had magnitudes between 3.4 and 4.1 and depths between 3 and 83 km (1.8 – 51 miles).

To protect the neighboring populations, authorities ordered geological-structural studies and the installation of a local seismic network near the volcano.

In addition, scientists were asked to update permanent seismic stations, take spring water samples for chemical analysis, and measure gas emissions among other measures, which include obtaining photogrammetric data via drones, etc.

Authorities are urging the population to remain calm, avoid rumors and be aware of the information disseminated by official sources.

The last eruption of this volcano took place from March 28 to September 11, 1982 (Volcanic Explosivity Index 5).

This volcano has a history of VEI 5 eruptions – in 2030 BCE ± 100 years, 780 ± 100 years, 1360 ± 100 years and 1982.

El Chichon volcano on December 31, 2020. Credit: Copernicus EU/Sentinel-2, RAMMB/CIRA, TW

Geological summary

El Chichón is a small, but powerful trachyandesitic tuff cone and lava-dome complex that occupies an isolated part of the Chiapas region in SE México far from other Holocene volcanoes.

Prior to 1982, this relatively unknown volcano was heavily forested and of no greater height than adjacent nonvolcanic peaks.

The largest dome, the former summit of the volcano, was constructed within a 1.6 x 2 km (1 x 1.2 miles) summit crater created about 220 000 years ago.

Two other large craters are located on the SW and SE flanks; a lava dome fills the SW crater, and an older dome is located on the NW flank.

More than ten large explosive eruptions have occurred since the mid-Holocene.

The powerful 1982 explosive eruptions of high-sulfur, anhydrite-bearing magma destroyed the summit lava dome and were accompanied by pyroclastic flows and surges that devastated an area extending about 8 km around the volcano.

The eruptions created a new 1 km (0.62 miles) wide, 300 m (984 feet) deep crater that now contains an acidic crater lake. (GVP)

Featured image: El Chichon volcano on December 31, 2020. Credit: Copernicus EU/Sentinel-2, RAMMB/CIRA, TW

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