Cause and risk of catastrophic eruptions in the Japanese Archipelago

The Japanese Archipelago is characterized by active volcanism with variable eruption styles. The magnitude (M)-frequency relationships of catastrophic caldera-forming eruptions (M >= 7) are statistically different from those of smaller eruptions (M <= 5.7), suggesting that different mechanisms control these eruptions. We also find that volcanoes prone to catastrophic eruptions are located in regions of low crustal strain rate (<0.5 x 10(8)/y) and propose, as one possible mechanism, that the viscous silicic melts that cause such eruptions can be readily segregated from the partially molten lower crust and form a large magma reservoir in such a tectonic regime. Finally we show that there is a similar to 1% probability of a catastrophic eruption in the next 100 years based on the eruption records for the last 120 ky. More than 110 million people live in an area at risk of being covered by tephra >20 cm thick, which would severely disrupt every day life, from such an eruption on Kyushu Island, SW Japan.