Once upon a time, between 5 and 6 million years ago, much of the Mediterranean Sea disappeared in what came to be known as the Messinian Salinity Crisis (MSL), named after the age it took place in. Weirdly, as a new Nature Geoscience study reveals, it likely triggered a series of powerful volcanic eruptions too.
It may seem odd that the two dramatic events had any connection – so in order to understand what it may be, let’s go back to when the crisis began.
The first half of this geological epic is well-known to scientists. Around 6 million years ago, the Strait of Gibraltar – the gap between Spain and Morocco that connects the Mediterranean Sea with the Atlantic Ocean – was closed off rather suddenly at the same time the area was experiencing a dry, warm climate. These factors meant that much of the water that evaporated off the sea was never replenished. As a result, it became a giant salt depository.
For several hundred thousand years, the Mediterranean Basin reigned supreme, with a sea level up to 5 kilometers (3.1 miles) deeper than normal. Any pools of water that remained were so salty that they proved to be deadly to most types of life.
Around 5.3 million years ago, the crisis ended when the Strait of Gibraltar opened up again, triggering an Atlantic Ocean-based multi-step waterfall that was over a kilometer (0.62 miles) high and had an outflow of around 1,000 times that of the modern-day Amazon River. Shortly afterwards, the Mediterranean Sea had returned.
An international team led by the University of Geneva suspected that this wasn’t all there was to the story. They suspected that such a massive loss of water would have had a rather bizarre secondary effect – namely, it would have triggered volcanic eruptions nearby.
The premise isn’t a new one. Volcanologists suspect that when ice melts off the top of a volcano, it alleviates the confining pressure on the magma chamber fueling it. This allows bubbles to form, which in turn increases the internal pressure of the magma chamber.
If this reaches a critical point, the encapsulating rock collapses and the volcano erupts. The same principle applies to the MSC too. With all that water gone, any underlying magma chambers would have experienced a huge drop in confining pressure – and, according to their numerical simulations, volcanism should have been more prominent back then.
The team needed to find several contemporaneous eruptions to back up this idea, and indeed they did: There were 13 eruptions around the Mediterranean at the time, twice the average volcanic activity in that part of the world.
Ultimately, this means that climate change has multiple ways of setting off volcanoes – something we’d do well to remember considering our prevailing addiction to fossil fuels.