FIELD OBSERVATION OF DEPOSITION OF PUMICE AROUND DETACHED BREAKATERS -AN EXAMPLE OF OGIMI COAST ON OKINAWA ISLAND

Abstract

 A underwater volcano, Fukutoku-no-oka, of Ogasawara Islands erupted on 13 August 2021. A large amount of pumice produced by this eruption was transported westward by the ocean current and reached the north part of Okinawa Island since 17 October 2021. At the Ogimi coast located in the northwest part of Okinawa Island, much pumice was deposited along the coastline burying the white sandy beach composed of coral sand. On 28 October 2021, field observation using a UAV was carried out to measure the distribution of floating and deposited pumice around the detached breakwaters. The thickness of the deposited pumice was measured using an RTK-GPS to be approximately 40 cm. Deposition of pumice was significant between the detached breakwaters because of closed sea.