Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Cover
Pumice Raft from August 2021 Eruption of Fukutoku-Oka-no-Ba Volcano, at Shidooke Beach, Kikaijima Island, Kagoshima
JOURNAL FREE ACCESS

2022 Volume 131 Issue 1 Pages Cover01_01-Cover01_02

Details
Abstract

 Fukutoku-Oka-no-Ba (FOB) volcano is a submarine volcano located in the southern Izu-Bonin Arc. Based on observation data collected by the Himawari-8 meteorological satellite, FOB volcano erupted from around 06:00 on August 13, 2021. The climax of the eruption occurred on the same day, generating an eruption column of about 16 km in altitude, which reached the tropopause. It was visible from the Ogasawara Islands, which are located more than 300 km away. Furthermore, aircraft observation by the Japanese Coast Guard found a new emergent island formed from the eruption on August 15. Formation of a new island at FOB volcano occurred for the first time since the 1986 eruption 35 years before. From the satellite observations, it was recognized that a large volume of pumice started to float with water discoloration in the proximity of the eruption center soon after the eruption began.

 Pumice is a highly vesicular, low-density, pyroclastic rock, which can float in water for long periods of time. A large volume of floating pumice (pumice rafts) generated from this eruption was transported west by currents and winds. It started to arrive at the Daito and Ryukyu Islands from early October, washing up on local beaches and coasts and causing hazards to fisheries and marine transportation.

 Kikaijima is located ∼20 km east of Amami-Oshima. It is a flat-topped island with thick Pleistocene limestone covering sedimentary rocks of the Pliocene Shimajiri Group. Radiometric ages of ca. 100 ka were obtained from fossilized coral at the highest plateau of the island (∼200 m above sea level), indicating rapid uplift of the island (Inagaki and Omura, 2006). Pumice rafts from the FOB eruption choked many complex inlets around the island, where they are expected to remain for a long period of time.

(Photograph & Explanation: Kenichiro TANI; Photographed on October 16, 2021)

© 2022 Tokyo Geographical Society
Next article
feedback
Top