Volcano-Tectonic Evolution of the Christiana-Santorini-Kolumbo Volcanic Field, Central Aegean Sea

Abstract

The Christiana-Santorini-Kolumbo volcanic field (CSKVF) in the southern Aegean Sea lies in an active continental rift zone and is one of the most hazardous volcanotectonic regions in the world. Here, the historic eruption of the submarine Kolumbo Volcano occurred in 1650 CE, as well as the iconic Minoan eruption in 1600 BCE, which is thought to have contributed to the fall of the great Minoan civilization. Extensive research in the last decades has led to a detailed understanding of the onshore volcanic history of Santorini. However, since most of the volcanic edifices and their deposits lie offshore, critical observation gaps regarding the volcano-tectonic evolution of the CSKVF remain. In this thesis, I exploit a dense array of highresolution seismic reflection profiles to address the following questions: How did the CSKVF evolve in time and space, and how did volcanism and crustal tectonics interact? What is the volume of the Minoan eruption and how did the eruption shape the seafloor morphology of Santorini? What processes led to the tsunamigenic eruption of the Kolumbo volcano? Can seismic diffractions support the depth conversion and interpretation of offset-limited seismic data? By linking the marine stratigraphy to onshore volcanic sequences, I present the first consistent seismostratigraphic framework for the CSKVF that allows linking the tectonic evolution of the rift basins to the evolution of the volcanic centers. I demonstrate that the CSKVF evolved from a volcanic field with local centers, and only matured in the last ∼350,000 years to form the vast Santorini edifice. Volcanism emerged in the Late Pliocene when an ESE-WNW-oriented tectonic regime was overprinted by a newly emerging NE-SW-directed rift system. Thereafter, all volcanic centers aligned parallel to this trend and evolved above distinct NE-SW-directed faults that cross-cut present-day Santorini. A major tectonic pulse occurred at ∼0.7 Ma, triggering a large mass-wasting cascade on the flanks of Santorini and Christiana, while another rift pulse at ∼0.35 Ma led a focus of volcanic activity on Santorini with increasing explosivity. In addition, the seismic reflection data enable the Minoan ignimbrites to be identified and mapped in the offshore domain. Combining these data with a multidisciplinary dataset comprising sediment cores and P-wave tomography data, allowed the calculation of the volume of the Minoan eruption, which is estimated to 31.4 ± 5.2 km3. This estimate is significantly smaller than previously assumed but consistent with an independent caldera collapse reconstruction. The emplacement of vast amounts of ignimbrites, as well as major slumping events during the Minoan eruption, caused the formation of large-scale undulating seafloor bedforms around Santorini. Further, high-resolution 3D seismic and bathymetry data show that the 1650 CE Kolumbo eruption was triggered by a major slumping event of its NW flank that depressurized the magma system, leading to a catastrophic explosion. This chain of events is supported by tsunami models that reproduce historic eyewitness accounts. Finally, I show that diffraction-based wavefront tomography, in combination with an interpretation-driven refinement, enables depth migration of offset-limited seismic data and that the focussed diffracted wavefield is a valuable tool for the interpretation of small-scale heterogeneities, e.g. faults and unconformities. Combining all results, this thesis highlights that tectonics, volcanism, and masswasting are fundamentally interconnected at the CSKVF and can trigger each other as hazardous disaster cascades. Shoreline crossing monitoring and early warning systems are urgently needed on the flanks of Santorini and Kolumbo to prevent the next major event from becoming a disaster.