Rising, falling sea levels linked to volcanic activity
The island of Thera in the south Aegean Sea, about 120 miles southeast of the Greek mainland, is a fragment of what used to be a much larger island produced by the volcano known as Santorini.
Around 3,600 years ago, late in the Bronze Age, Santorini exploded in one of the largest eruptions in recorded history. It expelled the equivalent of 15 cubic miles of rock, and produced huge tsunamis.
The cataclysm is blamed for the demise of the Minoan civilization, based on the island of Crete, just 68 miles to the south, which was buried by as much as 200 feet of volcanic debris. That may have been the origin of the story of Atlantis.
That eruption was not the first for Santorini. A recent bit of research by scientists from the United Kingdom and Sweden, published in the journal Nature Geoscience, examined the 360,000 year history of volcanic activity preserved there.
Looking at the record of eruptions in cores obtained by drilling in nearby marine sediments, whose ash layers can be precisely dated using radiometric methods, they discovered something interesting.
It has been known for some time that eruptions of volcanoes on land can be triggered or suppressed by the advance and retreat of overlying glaciers due to the weight of the ice. The new research showed the same thing occurs for ocean volcanoes when sea levels rise and fall – the weight of the water can suppress or release volcanic activity.
Numerical modeling had already indicated the weight of water could
It has been known for some time that eruptions of volcanoes on land can be triggered or suppressed by the advance and retreat of overlying glaciers due to the weight of the ice.
suppress or release volcanic activity. That weight is significant. At eight pounds per gallon, I realize how heavy it is every time I haul a jug of water up from the basement.
When sea level fell by more than 40 meters (about 130 feet), lava started working its way up into the rocks above the chamber. When sea level fell to minus 70 or 80 meters (-230 to -260 feet) eruptions occurred.
As sea level rose again, volcanic activity decreased: 208 of 211 eruptions occurred when sea level dropped.
It takes time for the changes in stress to propagate through solid rock, so the changes aren’t instantaneous. There is a time lag of about 30,000 years between sea level dropping below minus-40 meters and the start of eruptions. Also, because sea level rises much faster than it falls, there is a time lag of only about 11,000 years between sea level rising above the minus-40 meter mark and the cessation of eruptions.
The analysis suggests that Santorini might be entering a quiet phase. The magma chamber feeding Santorini is shallow, only about two and a half miles below the sea bottom. Other volcanoes have deeper magma chambers, so the stress should change more slowly, but still react to changes in sea level. That is significant because 57% of the world’s volcanoes are islands or along the coast, subject to pressure produced by rising and falling seas.