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San'in Kaigan NP, Hyogo
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Genbudo’s 1.61-million-year-old basalt preserves reversed magnetism. Motonori Matuyama detected it in 1926 and proposed geomagnetic reversals in 1929; the discovery later helped underpin plate-tectonic science.
The “caves” are quarry scars, not natural hollows: workers pried out basalt columns for sturdy building stone. The nearby Maruyama River made the heavy blocks easier to transport.
After the 1925 North Tajima earthquake and fires devastated Kinosaki Onsen, the town rebuilt the banks of the Otani River with basalt quarried at Genbudo—making the cave’s stone part of the town’s recovery.
The Japanese name for basalt, genbugan (玄武岩), comes from Genbudo: in 1884, geologist Koto Bunjiro named the rock after this quarry. A local place-name entered geology’s vocabulary.
In 1807, scholar Shibano Ritsuzan named the outcrop for Genbu, a tortoise-and-snake guardian whose form he saw in the columns. The 5 caves draw on China’s Four Symbols, with Suzaku split into north and south.
Seiryudo is nicknamed the “Music Cave” for its natural acoustics. Artists from different musical genres have held concerts beneath its basalt columns.
Genbudo is IUGS Geological Heritage Site No. 010, included among the organization’s first 100 sites recognized worldwide for their importance to the history of geology.
In nearby Akaishi, stone walls pair dark Genbudo basalt with local red rhyolite—known as “red stone.” The village’s masonry sets two very different regional volcanic rocks side by side.
A 1925 earthquake triggered a collapse on Genbudo’s north side, according to the San’in Kaigan Geopark’s history of the site. Even this famous cliff records the region’s seismic past.
