Underwater volcano in Antarctica sets off 85,000 earthquakes

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A long-dormant undersea volcano in Antarctica has erupted, causing an outbreak of 85,000 earthquakes. 

The swarm, which began in August 2020 and ended in November of that year, is the region's greatest earthquake activity ever recorded. According to a recent study, the quakes were most likely produced by a "finger" of hot magma probing into the crust.

Simone Cesca, the study's co-author and a seismologist at the GFZ German Research Centre for Geosciences in Potsdam, told Live Science that "there have been similar intrusions in other places on Earth, but this is the first time we have observed it there," adding that these processes usually occur over geologic time scales.

The swarm occurred on the Orca Seamount, an inactive volcano rising 2,950 feet from the seafloor in the Bransfield Strait, a short strait between the South Shetland Islands and Antarctica's northern coast. According to a 2018 research published in the journal Polar Science, the Phoenix tectonic plate is sinking beneath the continental Antarctic plate in this location, generating a network of fault zones, stretching certain parts of the crust, and forming rifts in others.

Scientists on King George Island, one of the South Shetland Islands, were the first to notice the rumblings of tiny earthquakes. The news quickly spread to Cesca and his colleagues all over the world, some of whom were working on other projects with the researchers on the island.

Researchers utilized data from two nearby seismic stations since King George Island is so remote, as well as data from ground stations for the international satellite navigation system.

Cesca stated that with the pieces of all the data coming together, enough information was gathered about the underlying geology triggering the earthquakes.

The series' two most powerful earthquakes were a magnitude 5.9 quake in October 2020 and a magnitude 6.0 quake in November. Seismic activity decreased following the November quake. According to the analysis, the quakes moved the earth on King George Island by around 4.3 inches (11 cm).

Cesca stated that "what we think is that the magnitude 6 somehow created some fractures and reduced the pressure of the magma dike."

Cesca said that if there was an undersea eruption at the seamount, it most likely occurred at that time. However, there is no clear proof of an eruption as of yet; to establish that the gigantic shield volcano blew its top, scientists would need to send a mission to the strait to measure the bathymetry or seafloor depth, and compare it to previous maps, he explained.