Lay summary
~160,000 years ago, one of the largest Quaternary explosive eruptions occurred off shore of the eastern Mediterranean island of Kos, during which >60 km3 of volcanic ash and pumice were emplaced as pyroclastic fall and flow deposits over an area >2000 km2. In comparison to the Minoan eruption on the nearby island of Santorini (e.g., Pyle, 1997), the Kos Plateau Tuff (KPT) was at least twice as large. Since the KPT eruption, several smaller but similarly explosive events occurred in the same area, indicating that the system continues to produce hazardous magmas. Although the repose periods for such volcanic systems are on the order of 103-104 years (increasing with increasing erupted volume), similarly cataclysmic eruptions will occur again in the Mediterranean basin and elsewhere, with devastating consequences on a regional or even hemispheric scale.
Whether a volcanic eruption of viscous, water-rich magma occurs as a (relative slow) effusion of lava or as a highly hazardous explosive burst of hot gases and volcanic pyroclasts depends primarily on how the magma behaves in the conduit prior to reaching the earth’s surface. If the conditions are such that bubble expansion is rapid, the magma may reach fragmentation (the process by which viscous, bubbly magmatic foam disintegrate into a low-viscosity particle-laden hot gas), triggering an explosive event. Understanding how magma ascends in conduits and how it fragments as a function of its physico-chemical characteristics is therefore fundamental to predict the impact of the eruption on human infrastructures and populations. Despite the fact that this area of research has been very active over the last decade, much remains to be done.
Juvenile pyroclasts of explosive silicic eruptions are the only available natural sample that preserves information on the state of magma at fragmentation. We propose to characterize the pyroclastic products from the KPT and its precursor (Kefalos pyroclastic series). These units are exceptional mines of textural information due to abundance of fresh, unconsolidated volcanic ash and pumice, and will permit a detailed comparison of pyroclasts from different eruptive styles, including (1) phreato-magmatic activity (early and late part of the KPT, Kefalos pyroclastic series), (2) a magmatic, central-vent? pre-caldera phase of the KPT, and (3) the magmatic, caldera-forming phase (climactic part of the KPT). The nature of the volcanic ash and pumice will be characterized using a number of different methods (including state-of-the-art 3-D reconstruction of the pore space structure by X-ray computed microtomography) and will lead to novel ways of interpreting eruption dynamics.