Santorini erupts at sea level

Recent studies have shown that when the sea level drops more than 40 meters below today’s level, it causes a cluster of eruptions from the Santorini volcano. When the sea level is higher, the volcano is calmer. The researchers suggest that the same may be true for other volcanoes scattered around the world — most of them in or near oceans.

“It’s hard to imagine why sea levels wouldn’t affect coastal or island volcanoes,” said Ian Stewart, a geologist at the Royal Jordanian Society of Sciences in Amman, who was not involved in the study.

Taking these effects into account can improve the accuracy of volcanic hazard prediction.

Santorini consists of a ring of islands surrounding the tip of the central volcano protruding from the Aegean Sea. The entire volcano was above water, but a violent eruption in about 1600 BC caused the volcano to partially collapse to form a lake. This particular eruption is known to have destroyed the Minoan civilization and inspired the myth of Atlantis.

To investigate how sea levels affect the volcano, scientists created a computer simulation of Santorini’s magma chamber, which lies about four kilometers below the volcano’s surface. In the simulation, when sea level fell at least 40 meters from the current level, the crust broke apart over the magma chamber.

“This gives the possibility that the magma that has built up under the volcano will move up through these fissures and rise to the surface,” said Christopher Sato, a physical geographer at Oxford Brookes University.

According to the simulation, it will take about 13,000 years for these fissures to reach the surface and awaken the volcano. After the water rises again, it should take about 11,000 years for the fractures to close and the eruptions to stop.

It would seem counterintuitive that lowering the amount of water at the top of a magma chamber would cause the crust to split. Sato compares this scenario to wrapping his arms around an inflated balloon, with rubber being the crust of the Earth and hand pressure inward as the weight of the ocean. When someone else pumps air into the balloon—like magma accumulating under the earth’s crust—hand pressure helps prevent the balloon from popping.

“Once you start releasing the pressure with your hands, as in lowering sea level, the balloon will expand and eventually explode,” Sato added.

Sato’s team tested simulation predictions by comparing the history of the eruption of Santorini with evidence of sea-level passage of marine sediments. All but three of the 211 volcanic eruptions over the past 360,000 years occurred during periods of low sea level, the simulation predicted. Periods of lower sea levels occurred when more of Earth’s water was trapped in glaciers.

Sato says volcanoes around the world are likely to be affected by changes in sea level, although their intensity is likely to vary. Some will be very sensitive to changes in sea level, and for others, changes in temperature will have no effect. These effects will depend on the depth of the magma chambers feeding each volcano and the characteristics of the surrounding Earth’s crust.

For Santorini, with the last time sea level was less than 40 meters below its current level about 11,000 years ago, and sea levels still rising due to climate change, the volcano is expected to enter a period of relative calm. However, scientists say that two major eruptions in the volcano’s history occurred at high sea levels, so future violent eruptions are completely out of the question.