Sciency Thoughts: Gunma Prefecture

Friday, 17 November 2023

Hoard of ancient and medieval coins unearthed in Japan.

Archaeologists carrying out a survey at a site in the Sojamachi District of Maebashi, the capital city of Gunma Prefecture, in the northern Kantō region of Japan ahead of a construction project have unearthed a hoard of about 100 000 coins, some of which are thought to be over 2000 years old. The coins were buried in 1060 bindles, each of which contained about 100 coins and was wrapped in straw matting, and are thought to have been buried during the Kamakura Period (1185-1333), during which Japan suffered a number of civil conflicts.

Some of the bundles of coins dug up in Maebashi, Japan. Eiichi Tsunozu/The Asahi Shimbun.

The majority of the coins are badly corroded, and need to be cleaned and examined very carefully. So far only 344 of the coins have been fully examined, with 44 types of coin so far identified. The most remarkable of these appears to be a Chinese Ban Liang coin (so called because it has the symbols Ban Liang, 半兩, meaning 'half tael' stamped upon it). These were the first coins produced in a unified Chinese Empire under the Qin Dynasty, from about 378 BC to about 249 BC, and then by the Western Han Dynasty until about 118 BC. The example in the Sojamachi hoard is thought to date from about 175 BC, and is 2.3 cm in diameter and a millimetre thick, with a square hole in the middle measuring 7 mm to a side.

A Chinese Ban Liang (半兩) coin thought to date from 175 BC, discovered at Maebashi in Japan. Eiichi Tsunozu/The Asahi Shimbun.

Eruption on Mount Kusatsu-Shirane kills one and injures at least fifteen.

One man has died and at least fifteen more have been injured in a rockfall triggered by an eruption on Mount Kusatsu-Shirane, a 2160 m stratovolcano (cone-shaped volcano made up of layers of ash and lava) in Gunma Prefecture on Honshū Island, Japan, on Tuesday 23 January 2018. The eruption occured at about 10.00 am local time, and resulted in rocks being thrown several hundrad meters into the air. The dead man, along with several of those injured, is described as having been a member of the Japanese National Defece Force who was on a training exercise at the time of the eruption.

Cloud of ash over Mount Kusatsu-Shirane following an eruption on 23 January 2017. Yomiuri Shimbun.

Japan has a complex tectonic situation, with parts of the country on four different tectonic plates. Kyushu Island lies at the northeast end of the Ryukyu Island Arc, which sits on top of the boundary between the Eurasian and Philippine Plates. The Philippine Plate is being subducted beneath the Eurasian Plate, in the Ryukyo Trench, to the Southeast of the Islands. As it is drawn into the interior of the Earth, the tectonic plate is partially melted by the heat of the Earth's interior, and liquid magma rises up through the overlying Eurasian Plate to form the volcanos of the Ryukyu Islands and Kyushu.

The movement of the Pacific and Philippine Plates beneath eastern Honshu. Laurent Jolivet/Institut des Sciences de la Terre d'Orléans/Sciences de la Terre et de l'Environnement.