A debris avalanche at Suphan stratovolcano (Turkey) and implications for hazard evaluation

The Quaternary Suphan debris avalanche deposit is located in Eastern Anatolia, Turkey. The avalanche formed by the sector collapse of a major stratovolcano towards the north, possibly during a single catastrophic event. The deposit has an estimated volume of 4 km(3) and ran out over 25 km to cover an area of approximately 200 km(2). Products of the collapse are overlain by younger eruptive units from the Suphan volcano. We have tested the numerical code VolcFlow to first reproduce the emplacement of the Quaternary Suphan debris avalanche and then to develop a hazard assessment for potential future sector collapses and subsequent emplacement of debris avalanches and associated tsunami. The numerical model captures the main features of the propagation process, including travel distance, lateral spread, and run up. The best fit obtained for the existing flow has a constant retarding stress of 50 kPa and a collapse scar volume of 4 km(3). Analysis of potential future collapse scenarios reveals that northern sector debris avalanches (up to 6 km(3)) could affect several towns. In the case of a sector collapse towards the south, a tsunami will reach the city of Van and several of the biggest towns on the southern shoreline of Lake Van. Cities most affected by the larger amplitude waves would be Van, Edremit, Gevas, Tatvan, and, to a lesser extent, Ercis, with wave amplitudes (first waves after the onset of the collapse) between 8 and 10 m.