Santorini shows signs of restlessness

The almost unbelievable beauty and visual drama of the Greek island group known as Santorini in the southern Aegean Sea is the result of a complex geological history. Santorini is the site of several shield volcanoes which overlap and are cut by a number of calderas created by successive very large explosive eruptions (180,000 years ago, 70,000 years ago, 21,000 years ago and 3,600 years ago). The most recent large eruption around 1650 BC was one of the most powerful of Holocene volcanic eruptions, with a VEI normally rated as 6 or 7. This eruption has been associated with the destruction of the Minoan civilization in nearby Crete, and certainly had a destructive impact across an extensive area of the eastern Mediterranean. Since that most recent caldera collapse event Santorini has periodically reminded everyone that it is still active, with smaller-scale (but locally destructive) eruptions in 1570, 1650, 1707 and 1866, generally involving submarine activity with dome extrusion, island formation, lava flows and phreatic explosions. During the twentieth century there was activity in 1925, 1928, 1939 and 1950. The site of recent activity has been Nea Kameni, which can be seen in the centre of the island group in the image above, which dates from 21 November 2000 and comes from the NASA Earth Observatory.

Santorini, then, is very much an active volcano, and there are currently indications that it is becoming restless once again. A team led by Dr Andrew Newman of Georgia Tech has been monitoring Santorini through a dense network of GPS stations since 2006. Over the past year, since January 2011, these instruments have detected a reawakening of the volcano. Newman’s team has published their observations in Geophysical Research Letters (papers in press). To quote from the abstract:

After approximately 60 years of seismic quiescence within Santorini caldera, in January 2011 the volcano reawakened with a significant seismic swarm and rapidly expanding radial deformation. The deformation is imaged by a dense network of 19 survey and 5 continuous GPS stations, showing that as of 21 January 2012, the volcano has extended laterally from a point inside the northern segment of the caldera by about 140 mm and is expanding at 180 mm/yr. A series of spherical source models show the source is not migrating significantly, but remains about 4 km depth and has expanded by 14 million m3 since inflation began.

An injection of fresh magma is clearly going on at depth. This may not produce eruptive activity at the surface at all (Professor Newman points out that other calderas around the world have shown comparable activity without erupting), but Santorini, a volcano with the potential to be very dangerous, is evidently getting restless once again.

• A. V. V. Newman, S. Stiros, L. Feng, P. Psimoulis, F. Moschas, V. Saltogianni, Y. Jiang, C. Papazachos, D. G. Panagiotopoulos, E. Karagianni, & D. Vamvakaris, ‘Recent geodetic unrest at Santorini Caldera, Greece’, Geophysical Research Letters, doi:10.1029/2012GL051286, in press (accepted 6 March 2012). [abstract]

News
Santorini: the ground is moving again in paradise – Georgia Tech news release, 13 March 2012 (duly recycled at ScienceDaily, esciencenews and probably elsewhere too)
Volcanic island of Santorini shows activity – Greek Reporter, 13 March 2012
Volcanic activity detected on Greek island – TG Daily, 14 March 2012
Volcano on scenic Greek island getting a little restless – msnbc.com, 14 March 2012
Greek volcano reawakens – ScienceNews, 14 March 2012

Information
Global Volcanism Program: Santorini – GVP information for Santorini (0102-04=)
ISMOSAV – Institute for the Study and Monitoring of the Santorini Volcano
Santorini Decade Volcano – Santorini profile from the Decade Volcanoes project