Pumice study may reveal cause of undersea eruption

Japanese researchers say the recent undersea volcanic eruption that spewed a large volume of pumice stones, might have been caused by mixing substances in a magma chamber.

The massive undersea volcanic eruption occurred in August in the Pacific near the Ogasawara Islands. Pumice stones began washing up in October along the southwestern coastline up through central Japan.

Shortly after the eruption began, a team led by Tamura Yoshihiko of the Japan Agency for Marine-Earth Science and Technology analyzed pumice stones taken from the sea surface about 300 kilometers west-northwest from the volcano.

The researchers found that the stones consist largely of trachyte volcanic rock. The substance was also found in pumice produced in a previous eruption at the volcano in 1986.

This time, the team also identified a minute volume of basalt, a volcanic substance that usually exists about 30 to 60 kilometers under the seabed in a magmatic form. Usually, basalt is not found in a magma chamber near the seabed.

Tamura said the substance in a hot, liquid form deep under the seabed may have moved up for some reason, then mixed with trachyte in the magma chamber.

He said this may be responsible for the recent explosive eruption that released a large volume of pumice.