Will she blow? Magma chamber inflation at Santorini caldera

By Rachel Berkowitz

All that is visible of the mostly submerged Santorini caldera, a cauldron-like volcanic feature, are a few exposed islands that trace a circular outline in the Aegean Sea.

The caldera began its volcanic activity some 600 000 years ago due to subduction along the Hellenic arc . The Minoan eruption in 1650 BC caused the then central island surface to collapse and form the present caldera. Over the past 2000 years small eruptions have continued to occur, and the five most recent dacite eruptions have led to dome growth and lava flows.

Since 1950, when central vent and regional fissure eruptions produced lava flows and explosive events, the popular tourist destination had seemed peaceful enough. But a year ago the submerged volcano reawakened with a swarm of seismic events and rapidly expanding radial deformation, all of which suggests that something is going on in the magma chamber system beneath the surface.

Deformation levels are measured by tracking the movement of more than 20 GPS stations placed on the islands. Seismic activity is recorded by a local network of 10 seismometers.

As of January 2012 the volcano had extended laterally from a point on its north side by about 140 mm and is expanding at 180 mm/year, according to a paper published this week in Geophysical Review Letters by Andrew Newman of the Georgia Institute of Technology and his collaborators.

Models based on simple volumetric changes of spherical sources suggest that the source of deformation remains about 4 km deep below the volcano and has expanded by 14 million cubic meters since the inflation began. Santorini’s unprecedented amount of deformation could indicate that a huge volume of magma has found its way from Earth’s mantle into a reservoir beneath the surface.

The volcano will not necessarily erupt, however. Other similar calderas have experienced comparable deformation activity without imminent eruption.

Compared with the 1650 BC eruption, the current source growth event involves a much smaller volume of magma, which is not sufficient to cause a repeat of that large-scale event. Rather, it could lead to a much smaller eruption or contribute to long-term dome growth.

If the volcano does erupt, the ashfall and earthquake activity could be catastrophic for boat traffic in the caldera and for homes along the cliffs. For now, geophysicists will keep monitoring seismicity and deformation. The residents of Santorini will have to wait and see what happens.