Falling sea levels in the Mediterranean led to unstoppable volcanic eruptions 5 million years ago

Falling sea levels in the Mediterranean tripled the number of volcanic eruptions in the area between 5 and 6 million years ago.

A total of 13 eruptions took place in this million-year period of history in the Mediterranean, a study in the journal Nature Geoscience finds. Normally there are between 4 and 5 eruptions every million years.

The trigger of this unusual period of volcanism was the Mediterranean Sea drying out, after it was cut off from the Atlantic Ocean. The local climate meant that the Mediterranean dried out and wasn't replenished, leading to dramatically lower sea levels.

This was known as the Messinian salinity crisis. Previous evidence for the Messinian salinity crisis includes very thick layers of salt found deep in the sediment of the Mediterranean area. When the water evaporated during the period of drying, the salt was left behind and formed a tell-tale thick layer.

Less water on the surface of the Earth in this region meant a lot less pressure on the crust. This lowered pressure on the mantle beneath the crust encouraged magma formation. More magma eventually means more eruptions.

"The single logical explanation is the hypothesis that the sea dried out, since this is the only event powerful enough to alter the Earth's pressure and magmatic production over the entire Mediterranean," said study author Pietro Sternai of the University of Geneva and the Department of Earth Sciences in UNIGE's Science Faculty.

Sternai and his colleagues carried out computer simulations to investigate the effect of sea level changes on the magma below.

"The simulations showed that the only way to account for the proven increase in volcanic activity was that the level (and thus the weight) of the Mediterranean Sea dropped by about two kilometres," said Sternai. "I leave it to you to imagine what the landscape looked like."

The findings suggest that surface-level changes to climate could potentially have significant effects on volcanic activity. It's been known for many years that volcanic activity can affect the Earth's climate, but much less evidence that the relationship works the other way as well.