Geodetic Characterization of Santorini Caldera From Continuous GPS Measurements

Santorini Caldera, in the southern Aegean, is part of a well developed, and very active volcanic system fueled by subduction along the Hellenic arc. The caldera is partially submerged, with only pieces of caldera wall, flanks, and central post-caldera lavas exposed above the sea level comprising a grouping of five small islands. The system had its most recent caldera-forming event around 1650 B.C. in a massive series of Plinean eruptions that expelled some 60 km3 of volcanic material, burying the previous island surface. The system remains active with ongoing smaller pyroclastic and phreatic eruptions, forming the central islets atop of the submerged caldera floor. In late-spring 2006, with UNAVCO field support and support form the Santorini Volcano Observatory, a network of two continuous GPS monuments spanning the caldera was established, and completion of a third monument is planned for this coming year. Additionally, 18 existing and new geodetic markers were first established with GPS across the 5-island group in 2006. These locations cover the caldera rim and flanks, and the central volcanic flows. Preliminary data from the two continuous GPS sites suggest that deformation across the caldera is currently minimal, and below the detection threshold for the 1.5 year continuous network. Through continuing analysis of the continuous network, along with additional campaign measurements, we hope to establish the temporal character and spatial extent of potential deformation in the volcanic complex, and determine if there exists any significant transient deformation associated with ongoing magma movement or edifice cooling. Monitoring such a rate over time may be useful for early hazard awareness and mitigation during regional volcanic crises.