Genbudo Cave

Genbudo is one of the Quaternary Monogenic Basalt volcanoes in central Japan. The lava of Genbudo Cave is 1.61-Ma alkaline basalt (Genbudo Research Group, 1991; Kawai and Hirooka, 1966). It exhibits spectacular columnar jointing reflecting its complex cooling history. In 1926, Dr. Motonori Matuyama discovered that the basalt of Genbudo Cave exhibited magnetic polarity opposite to the present geomagnetic field. This discovery led to the recognition of the presence of a period of the earth’s magnetic field opposite to the present, and in 1929, he proposed “geomagnetic reversal polarity” (Matuyama, 1929). The geomagnetically reversed period, including the age of Genbudo, was named “Matuyama Reversed Chron” in the 1960s, whose start corresponds to the beginning of Quaternary.

Ritsuzan Shibano, a Confucian scholar, visited Genbudo Cave in 1807 and named it Genbudo because he compared the outcrop’s irregularly oriented columnar joints to a Chinese legendary animal, Genbu (black tortoise). In 1884, Koto Bunjiro named the basalt “Genbugan” in Japanese from Genbudo, whose Chinese characters are used also in China. In 1931, Genbudo Caves were designated as a national natural monument. Since then, they have been preserved and managed as educational sites, accessible only for research