| Summary: | Santorini Volcano, the site of the catastrophic Minoan eruption in Greece, exhibits two distinct eruptive styles: small, effusive eruptions occur relatively frequently and build shields and domes of lava, whereas large explosive eruptions occur rarely, at intervals of 10,000-30,000 years. Both types of eruption were thought to incubate in a shallow magma chamber that is continually charged by small batches of melt injected into the chamber from below. However, petrological work suggests that at least 15% of the material ejected during the Minoan explosive eruption arrived in the magma chamber less than 100 years before the eruption. Here we use Satellite Radar Interferometry (InSAR) and Global Positioning System (GPS) measurements of surface deformation at Santorini to show that 10-20 million m 3 of magma have been intruded beneath the volcano since January 2011. This volume is equivalent to 10-50% of the volumes of recorded dome-forming eruptions. GPS and triangulation data show that this is the only volumetrically significant intrusion to have occurred since 1955, shortly after the last eruption. Our observations imply that whether Santorini is in an explosive or dome-forming phase, its shallow magma chamber is charged episodically by high-flux batches of magma. The durations of these events are short in comparison with the intervening periods of repose and their timing is controlled by the dynamics of deeper magma reservoirs.
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