Capturing a new episode of unrest at Santorini volcano, Greece

Santorini is a major volcano in the Aegean sea (Greece), which is best known for a major eruption (the Minoan eruption) that occurred about 3,600 years ago, and has been implicated in major environmental and political impacts across the eastern Mediterranean.

Since that eruption, which formed a large caldera, now flooded by the sea, volcanic activity at Santorini has been restricted to a small region in the middle of the caldera. Over the past 500 years, six moderate eruptions have taken place, forming the young islands of Nea and Palea Kameni. These eruptions have usually happened with little warning - a few very small earthquakes; some movements of the islands (up and down), and some changes in the seawater around the many hotsprings in the area. Each of these eruptions has involved the slow squeezing out of lava, with a few more dramatic explosions and the ejection of blocks of lava, ash and noxious gases. The last, and smallest, of these eruptions took place in 1950.

Since 1950, Santorini has been quiescent - with very few earthqaukes, and very little gas emission. Recently, during fieldwork, we measured a large increase in gas emission rates from near the youngest volcanic vent. We have also now seen some rapid movements of the main island of Santorini (measured by GPS), and of New Kameni (measure by satellite): these show that the islands are being lifted up by a few centimetres per month. There has also been a major swarm of very small earthquakes, some of which have been large enough to be felt by the residents of the islands.

We think that all of this evidence shows that Santorini has begun a significant phase of 'unrest'. The pattern of unrest that we have seen is similar to the signals reported that happen before some of the historical eruptions, amd we propose an intensive field campaign to measure the ground deformation and gas emissions, associated with the inflation of this major caldera volcano.

Because there have been very few opportunities for scientists to monitor the behaviour of caldera volcanoes during periods of unrest, we really don't yet know how to distinguish between background activity, and activity which might happen before an eruption, at least until just a very short time before an eruption happens. For this reason, we wish to use this rare opportunity to measure the changes with a shallow disturbance at a quiescent but dangerous volcano.

This research will be of benefit to anyone concerned with hazard assessment and monitoring of volcanoes; in particular restless or quiescent calderas.

Beneficiaries:

In Greece: the scientific agencies and universities involved in monitoring of Santorini and other young volcanoes, including IGME, the Hellenic Centre for Marine Research and the Institute for the Monitoring of Santorini Volcano, ISMOSAV.

On Santorini: through contacts with IGME, HCMR and ISMOSAV, our work will benefit the decision makers and tourist agencies of the islands of Santorini, by informing them of the 'intra-eruptive' behaviour of the volcano, and through a better understanding of the features that can happen during the background activity of a restless volcano.

Elsewhere: volcano observatories with responsibility for monitoring large restless volcanic systems, including USGS, USA (Yellowstone, Long Valley), INGV, Italy (Campi Flegrei), and others around the world.