Does sea level influence the eruption frequency of island volcanoes?

This NERC grant in kind provided £56,000 worth of Argon Isotope dating at the NERC isotope facility in East Kilbride, Glasgow. The aim of the work was to refine the chronology for the volcanic island of Santorini to test geophysical models which implied that sea level change on glacial-interglacial timescales could influence eruption frequency and/or style.

Argon Isotope dating is a technique through which the age of volcanic rocks and ashes can be determined with high precision (to within 2-5%). The Greek island of Santorini displays excellent evidence of 250,000 years of eruptions, and geophysical models imply that these eruptions may be influenced by the large (over 100m) sea level changes which occur as the earth moves from a glaciated (ice age) state to an interglacial state (e.g. now) and back again. The models implied that lower sea levels would result in more frequent, low magnitude eruptions because the lower the mass of water on the crust, the easier it is to create the fractures required for the magma to escape. Testing this theory with the island of Santorini required comparison of a precisely dated history of eruptions (the Argon Isotope dates combined with dates from other techniques) with a sea level record (already known) over the last 250,000 years.

A comparison of the empirical evidence from the sea level and eruption records confirms the prediction of the geophysical models that lower sea levels facilitate more frequent, lower magnitude eruptions. Conversely higher sea-levels restrict the ability of the crust to fracture and therefore only allow the largest, infrequent eruptions to occur. This result has very important for the hazard assessment of the island because it implies that as we are now in a time period of high sea levels the hazard assessment should assume large, low frequency eruptions rather than small high frequency eruptions.