A magnitude 3.6 earthquake has been recorded at the supervolcano Campi Flegrei, which sits around nine miles from Naples. Campi Flegrei is one of the world's most populated active volcanoes, with over 2.2 million people living within around three miles of the site.
The earthquake was reported at approximately 7.45 p.m. by the INGV, Italy's earthquake monitoring body. It struck at a depth of around 1.8 miles.
The largest earthquake to hit Campi Flegrei in 2021 was a magnitude 3 in May. There was a magnitude 4 earthquake in August 2017. The biggest earthquake to hit the area was a magnitude 4.2 event in 1984.
Volcanic activity in the region relates to the convergence of the African plate and the Eurasian plate. The volcano consists of 24 craters and edifices.
Campi Flegrei's last eruption was a fairly small event in 1538. This event, known as the Monte Nuovo eruption, was preceded by years of huge uplift of the ground, with the land at the center rising by tens of feet out of the sea. According to the U.S. Geological Survey, in the hours before the eruption, the shore rose so fast that fish were trapped and the coastline moved 1,200 feet into the sea.
On the day of the eruption, a crack opened in the uplifted area, releasing huge amounts of pumice, fire and smoke.
The volcano has also produced much larger eruptions, with one 40,000 years ago being classed as a "super-colossal" eruption. This is one down from the "mega-colossal" eruptions recorded at Yellowstone.
In the last 60 years, the region has shown signs of unrest, with uplift recorded at the site. Scientists have said the volcano could be entering a pre-eruptive state, with magma accumulating beneath.
While scientists say this does not mean an eruption is imminent, it could mean there will be one at some point in the future, so should be used in mitigation plans for the area. If and when the volcano does erupt, models indicate it could produce a 100-foot tsunami that would severely impact coastal areas like Pozzuoli and Sorrento.
In research published in Scientific Reports in February, scientists looked at the patterns of seismic activity at Campi Flegrei to estimate the mechanisms involved. They analyzed six earthquake swarms that have taken place over the last two decades.
Findings showed these swarms were associated with stress related to uplift at the caldera. They said they believe the current unrest is the result of the gradual increase of activity at a wide hydrothermal system at the Pisciarelli Fumarole Field.
Anna Tramelli, from Italy's National Institute of Geophysics and Volcanology, told Newsweek that ongoing tectonic earthquakes are part of the activity at Campi Flegrei. She said earthquakes at the volcano are not an alarming signal of activity.
"An alarming signal would be a migration towards the surface or a local surficial deformation," she said.
Correction 03/30/2022 5.46 a.m. ET: This article has been corrected to say the earthquake was a magnitude 3.6 event.
This article has been updated to include quotes from Anna Tramelli.
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