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Open Access

Gravity structure of Akan composite caldera, eastern Hokkaido, Japan: Application of lake water corrections

Earth, Planets and Space200961:BF03353205

Received: 1 October 2008

Accepted: 9 January 2009

Published: 31 August 2009


Akan volcano, eastern Hokkaido, Japan, is characterized by a rectangular-shaped caldera (Akan caldera: 24 km by 13 km) with a complex history of caldera-forming eruptions during the Quaternary. A new Bouguer anomaly map of the caldera is presented on the basis of a gravity survey around Akan volcano. As part of and in addition to this survey, we applied gravimetry over the frozen caldera lake including lake water corrections. The Bouguer map shows the distribution of at least three sub-circular minima indicative of multiple depressions inside the caldera. Lake water corrections, performed by a numerical integration method using rectangular prisms, sharpen edges of the sub-circular minima. This gravity feature is consistent with geological investigations suggesting that caldera-forming eruptions of Akan volcano occurred from at least three different sources. It is concluded that Akan caldera can be described as a composite caldera with three major depressed segments.

Key words

Gravity anomalyAkan volcanocomposite calderalake water correction