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What is the San’in Kaigan Geopark ?

The San’in Kaigan Geopark has had diverse geological and geomorphological features developed through the periods from the time when the Japanese Archipelago was a part of the Eurasian continent, the development of the Sea of Japan and to the present. Based on the background brought by these diverse features, there, also, are unique people’s lives, culture and history in the region.

San’in Kaigan Geopark Newsletter

2023/12/18/
NewsletterVol-19

International geological significanse

Genbudo Cave is the place that led to the discovery of the period of reversal of the earth's magnetic field in the early Quaternary.

Based on the study of the basalt sample collected at "Genbudo" in Toyooka City, Hyogo Prefecture, it was discovered that there was a time when the earth's magnetic field was reversed for the first time in the world. In 1926, Dr. Matuyama of the Kyoto University discovered that the basalt lava erupted from volcano about 1.6 million years ago was magnetized in the opposite direction of the current earth's magnetic field.

This discovery indicated that there was a period in which the earth’s magnetic field was opposite to what it is today. This period is called “Matuyama reversed chron” (dated about 2.6 million to 0.77 million years ago), and the discovery of the reversed period of geomagnetic field has greatly contributed to the development of the theory of the plate tectonics.

In June 2009, an international agreement was made to recognize the Matuyama reversed epoch (Matuyama chron) as indicating the beginning of the Quaternary era. The periods from about 770,000 years ago, the end of the reverse magnetic period, to the present, the earth's magnetic field is the same as it is now. But during that period, the geological age from about 770,000 to 130,000 years ago was ,further, named as "Chibanian". In this way, the change in the direction of the earth's magnetic field is also used as one of the indicators that determine the boundary of the geological age.

国際的な重要性

Dr. Motonori Matuyama

国際的な重要性

In the first half of the Quaternary, the direction of the earth's magnetic field was opposite.

  • 国際的な重要性

    The Genbudo Cave (basalt) was formed by volcanic eruption about 1.6 million years ago.

  • 国際的な重要性

    The Genbudo cave receives many visitors from abroad.

About the efforts of the council

In San'in Kaigan Geopark, by making best use of geoheritage and local resources through activities of conservation, education, tourism and local industry, various activities aiming at establishing sustainable community are conducted in collaboration with local resident, private company and local government.

協議会の取り組みについて