was the mainly homogeneous Osumi Pumice Fall (named because the pumice fall extended across the Ōsumi Peninsula to the south east). Above the Osumi pumice fall deposit, is the second phase Tsumaya pyroclastic flow deposit which is wholly confined within the pre-Aira basin. The Tsumaya pyroclastic flow buried the pre-Aira topography such as box canyons (formed by older pyroclastic flow deposits). The maximum thickness in the caldera is in the Kokubu area with the average thickness being or less. The Tsumaya pyroclastic flow consists of a "pale pinkish brown glass matrix containing a small amount of pumice and lithic fragments" consistent with the Osumi pumice fall and the Tsumaya pyroclastic flow occurred from the same vent. There was only a very short period between the Tsumaya pyroclastic flow and the formation of the present caldera in the Ito eruption. In contrast the Ito pyroclastic flow extends outside the basin as well as occupying inside the basin. The Aira-Tn tephra falls from this eruption were up to thick in the south east and this and Ito Ignimbrite up to thick, are the most significant pyroclastic deposits. The depth of the ash fall over the whole island of Kyūshū was over and more than for much of Japan Volcanic activity The relationship between Aira and Kirishima Magmatic systems Aira caldera is one of the most active and hazardous calderas in the world. It is home to the Kirishima volcanoes, a group of active volcanoes at the north end of Aira caldera. One of these volcanoes, Shinmoedake, has produced two strong magmato-phreatic eruptions, separated by almost 300 years. Starting in December 2009, active diving and inflation before the outbreak were noticed. A series of sub-plinian events then occurred from January 19th to the 31st. The first phase (eruption climax) was accompanied by a strong co-eruptive deflation. Aira Caldera may respond to small eruptions that come from a common reservoir. However, not all the volcanic systems are connected all the time as magma pathways open and close. The connection between Aira and Kirishima represents the clearest example of volcano interconnectivity revealed by geodetic monitoring. The inflation of one volcano can enhance the eruption probability of a neighbouring volcano. The subduction of the Philippine sea plate beneath the Eurasian plate is the reason for the active volcanism. Aira Caldera and Kirishima's magma storage is linked through tunnels that extend horizontally over tens of kilometers which