Sea Turns Red Around Italy's Supervolcano Campi Flegrei

The sea around Italy's supervolcano Campi Flegei turned red, signalling possible volcanic activity beneath the water.

The volcanic crater lake—the Averno—n Pozzuoli, near Naples, turned red last before spreading to wider stretches of the sea in the Gulf of Pozzuoli.

The vibrant red color is caused by microscopic algae that thrive in warmer temperatures. The harmful algae can be particularly toxic to fish and other wildlife in the area. It is a phenomenon that occurs seasonally in the area, however according to Volcano Discovery, this year, the algae bloom is particularly vibrant.

The rapid algae bloom may be linked to activity from Campi Flegei, the supervolcano that lies about nine miles from Naples. Campi Flegei is one of the most populated active volcanoes. It is made up of 24 craters and edifices, and appears as a large depression on the surface of the land. Around 2.2 million people live within three miles of the site.

Enzo Buon captured photographs of the phenomenon and posted them to Facebook.

Enzo Buono captured photos of the red sea

The link between these algae blooms and volcanic activity has not been widely documented, however, some scientists believe that extreme heat flow caused by volcanic activity can trigger the bloom. The heat from the volcano may have caused nutrients, that lie in the deep sea, to rise up and begin fertilizing the algae, causing its rapid expansion and the vibrant red color.

The bloom may be a cause for concern as the volcano has caused a flurry of earthquakes in the area in the past 30 days.

This included two earthquakes with a magnitude of 3.5 and 3.6, which were felt by many local people. The biggest earthquake to hit the area in recent decades was a magnitude 4.2 event in 1984.

The volcano has also shown wider signs of unrest in the last 60 years. Experts have said that this does not mean an eruption is imminent, however the increased activity at the site could signal that the volcano is entering a pre-eruptive state. This means there could be an eurption at some point in the future.

Scientists have said an eruption could cause a 100-foot tsunami that would severely impact coastal areas like Pozzuoli and Sorrento.

The volcano last erupted in 1538 following a century of mounting pressure. It lasted for over a week. However this eruption was quite small compared to those Campi Flegrei can prodice.

Around 40,000 years ago, it produced a "super-colossal" eruption, which is the second highest measure on the volcanic explosivity index, the first being "mega-colossal."

Campi Flegrei
A photograph shows a view of Campi Flegrei, Italy's supervolcano Ivan Romano/Getty Images