Jokulsarlon lagoon. The Breidamerkurjokull glacier has been retreating since about 1920. The lagoon formed at the glacial front shows a yearly increase.| J-STAGE
Palagonite ridge formed by subglacial eruption. Langjokull glacier in the background.| J-STAGE
Lakagigar fissure eruption. The 1783-84 Laka- gigar eruption resulted in a great famine, due to which Iceland lost 20% of its population.| J-STAGE
Valley of Eldgja. The 934-40 Eldgja eruption occurred along a 75 km-long fissure.| J-STAGE
Gullfoss waterfall. The two-step cataract has a total drop of 32 m.| J-STAGE
The braided course of the Jokulfell downstream from Hofsjokull.| J-STAGE
Geyser Strokkur. The geyser erupts at 5-10 minute intervals.| J-STAGE
Reykjavik is a smokeless city. Almost 100% of the electricity and the heating depends upon hydropower and geothermal energy.| J-STAGE
Normal fault at Thingvellir. The boundary between the North American plate on the left-hand side and the Eurasian to the right.| J-STAGE
Basaltic lava field, the Svartshengi geothermal power plant (right), and the Blue Lagoon (left).| J-STAGE
Earth hummock. Earth hummocks are among the periglacial phenomena. The knoll covered with vegetation is |about 0.5 m high.| J-STAGE
Dettifoss waterfall. The waterfall is 44 m high. The river water is rich in suspended sediments and the waterfall volume is the greatest in Iceland.| J-STAGE

Latest Issue

2022 Vol.131 No.1

Pumice Raft from August 2021 Eruption of Fukutoku-Oka-no-Ba Volcano, at Shidooke Beach, Kikaijima Island, Kagoshima

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)

Reference

[Inagaki, M. and Omura, A. (2006): Uranium-series age of the highest marine terrace of the upper Pleistocene on Kikai Island, central Ryukyus, Japan. Quaternary Research (Daiyonki-Kenkyu), 45, 41-48. (in Japanese with English abstract)]