Earth science: Sea-level changes affect Santorini volcanism

Intervals of low global sea level have influenced the timing of eruptions from the Santorini volcano in Greece over the past 360,000 years, according to a study published in Nature Geoscience.

The behaviour of magma chambers that feed into eruptive volcanoes is, amongst a range of other factors, influenced by downward pressure from overlying material. Erosional and tectonic processes that remove or add sediment can potentially modify eruptive activity over long periods of time. On timescales of several thousand years, fluctuating levels of surface water (in the ocean or within glaciers) might also displace enough mass to impact magma chambers. However, the importance of these changes — often linked to global climatic conditions — on the timing and severity of volcanic eruptions, is not well-understood.

Chris Satow and colleagues compared approximately 360,000 years of records chronicling eruptions of the Santorini volcano with high-resolution global sea level records throughout the last four glacial cycles. Previous research on tephra (pumice or ash) layers preserved in marine sediments near the volcano provided a time-resolved archive of 211 past eruptions, ranging from violently explosive to more effusive. The team found that 208 of these eruptions occurred after the sea level fell to at least 40 metres below present-day levels — a phenomenon that regularly occurred due to the expansion and contraction of large ice sheets on land. Numerical modelling revealed that when this sea-level threshold is surpassed, enough tensile stress is created at the top of the Santorini magma chamber to fracture the crust and allow for the upward propagation of magma through dykes. Some of these dykes reach the surface, causing eruptions.

The authors conclude that, with sea levels having risen since the last ice age and now also rising due to global warming, the relatively small eruptions of Santorini’s recent past may cease, but the threat of large explosive eruptions remains. They also emphasize the need to consider past sea-level changes when assessing volcanic hazards around the world.