Aira Caldera was created 22,000 years ago after a large scale of pyroclastic surges. The eruption of the Caldera assisted in its formation creating its total area of 17 x 23km. The formation of Aira Caldera started with a Plinian Pumice Eruption and was quickly followed by an oxidised Tsumaya pyroclastic flow (Aramaki, S. 1984). Basement rock fragments and pumiceous materials from a violent explosion formed the Ito pyroclastic flow about 300km3 in volume (Aramaki, S. 1984). The Caldera is known for its gravitational anomalies which have caused a funnel-like shape in the strata.