What a rimstone pool is
A rimstone pool is one of a series of dish-shaped pools where water carrying calcium carbonate flows: the deposited carbonate builds up a raised rim, like the bund of a paddy field, holding water within, and the pools step down one below another like terraced fields. They are common on the floors of limestone caves where water flows gently.
They form as calcium carbonate precipitates from the water and accumulates. The commentary on the travertine terraces at Bora on Miyakojima, Okinawa, explains that calcium carbonate in spring water is deposited as travertine as the water evaporates, forming small pools rimmed with travertine one after another. Such formations outside caves are called travertine terraces and are said to be rare in Japan.
Reading the records and the site
Akiyoshido in Mine, Yamaguchi, a limestone cave formed by solution and one of the largest in Japan, is a Special Natural Monument. Mine City describes one of its famous sights, the Hyakumaizara or hundred plates, as a huge rimstone pool of unrivalled beauty. The travertine terraces at Bora on Miyakojima, spreading about 70 by 30 metres at the foot of a cliff, are the largest open-air travertine terraces in Japan and a Natural Monument.
On site, look for shallow dish-like pools stacked in steps, their rims built up in pale calcareous deposit.
References
Last verified: 2026.09.27