A fall in the level of the Mediterranean Sea about 6 million years ago may have triggered volcanic eruptions in the region, according to a study published online this week in Nature Geoscience.
Vast salt deposits exist beneath the Mediterranean seabed. These deposits are thought to have formed when the Mediterranean Sea became isolated from the Atlantic Ocean about 5 to 6 million years ago, leading to evaporation and sea-level fall in an event known as the Messinian salinity crisis. The rate and amount of sea-level fall in the Mediterranean during this time is debated. However, if the sea-level drop was dramatic and rapid, it could have unloaded Earth’s surface, decompressing the mantle below. Such mantle decompression can enhance magma production and, in turn, lead to volcanic eruptions at the surface.
Pietro Sternai and colleagues test this idea using a combination of geological data and numerical modelling. They compile existing data on the timing of magma intrusions and volcanic eruptions in the region, and show that there was a pulse of increased volcanic activity towards the end of the Messinian salinity crisis. The researchers calculate changes in the surface load caused by a kilometre-scale drop in sea level, taking into account the counter weight of the increased density of the remaining highly saline water and accumulating salt deposits. They then use a numerical model to verify that such changes in sea level would have been sufficient to unload and decompress the mantle, triggering increased volcanism in the Mediterranean.
The results provide independent support the idea that sea-level fall during the Messinian salinity crisis was rapid and occurred on a dramatic scale, and also highlight the sensitivity of Earth’s solid interior to changes at the surface.
In an accompanying News & Views article, Jean-Arthur Olive writes that “This proposed link will motivate the collection of high-resolution field data that better constrain the timing of volcanism in the Mediterranean, along with the development of novel approaches for coupled lithosphere-magma dynamics.”