An international research team has discovered previously unknown deposits from an eighth century volcanic eruption in Santorini, which could have major implications for hazard planning around the world. 

The researchers, including Keele’s Dr Ralf Gertisser, were part of the International Ocean Discovery Program (IODP) Expedition 398 Hellenic Arc Volcanic Field, finding evidence of an explosive eruption of the Kameni Volcano in Santorini, Greece, which they linked to a historical explosion in 726 CE. 

The eruption took place under the sea and left behind considerable pumice and ash deposits below the sea floor inside Santorini caldera, a large crater formed by a previous volcanic eruption, which the scientists were studying to learn more about the eruption, and the volcano itself. 

Publishing their findings in Nature Geoscience, the researchers report on these newly discovered submarine eruption deposits that support historical writings about the eruption, which produced pumice rafts that covered the sea over an immense area reaching the coasts of Asia Minor, over 400 km away.  

Santorini has been active for approximately 650,000 years and is classified a multi-cyclic caldera volcano. Caldera cycles typically comprise phases of rejuvenation through new magma injections after caldera collapse, with subsequent small but frequent eruptions. This is followed by a build-up stage with few eruptions over many thousands of years before a climactic eruption triggers another caldera collapse. 

The last caldera-forming eruption in Santorini was the Late Bronze Age or Minoan eruption of around 1600 BCE. This eruption is a pivotal event not only in volcanology but also in archaeology, with scientists believing it may potentially have contributed to the decline of the Minoan civilization that populated the island of Crete.   

But deep sea drilling on the site conducted by the researchers in this study has unveiled a 40-metre-thick pumice layer inside the caldera, which challenges the previous understanding of Santorini’s volcanic behaviour. 

The findings suggest that Santorini Volcano is capable of larger explosive eruptions during the early stages of a caldera cycle, which has important implications for hazard assessments of recharging volcanic systems following a large caldera-forming eruption, both locally and globally, and even though there is no imminent danger of a significant eruption in Santorini, the researchers say it offers a “worst-case eruptive scenario” that should be considered in future hazard assessments. 

Dr Gertisser, Reader in Mineralogy and Petrology, said: “The surprising new finding of a larger explosive eruption of Santorini shortly after the caldera-forming event in the Late Bronze Age challenges our views how multi-cyclic caldera volcanoes like Santorini work. It must be emphasized though that while an explosive eruption like that in 726 CE may be regarded as a worst-case future eruption scenario for Santorini, there are currently no indications that such an eruption will happen any time soon.”