Volcanic block presumed to be a breadcrust volcanic bomb discovered in Jogashima, Kanagawa Prefecture

Abstract

In the "Earth Science Experiment" class at the Tokyo University of Agriculture, field observations are conducted for one day in Jogashima, Miura City, Kanagawa Prefecture. In the field training conducted in May 2022, volcanic block presumed to be a breadcrust volcanic bomb was discovered in the scoria layer of the Misaki Formation. In general, volcanic bombs erupt as masses of magma larger than 64 mm in diameter, and volcanic bomb, volcanic block and lapilli with ballistic trajectories have an average reach of less than 2 km, and reach more than 5 km from the volcanic crater is considered to be rare (Blong 1984). According to Ui (1997), cinder and volcanic bomb cause disasters within a radius of 2 to 3 km from the volcanic crater. Volcanic block presumed to be a breadcrust volcanic bomb with a diameter of more than 64 mm discovered this time indicate that a volcano with a crater above sea level was within a radius of about 10 km from Jogashima. This suggests that it has important implications for estimating the location of source volcano.