What a doline is
A doline is a bowl-shaped hollow on the surface of a limestone plateau. The Chugoku-Shikoku branch of the Japan Society of Engineering Geology describes it as a depression formed along the routes by which rainwater seeps underground or by the collapse of a cave below, also called a sinkhole, ranging from a few metres to several hundred metres across.
Limestone slowly dissolves in rain and groundwater containing carbon dioxide. Where water drains down through cracks in the surface, more rock is dissolved and the ground sinks. Dolines are regarded, together with Karrenfeld and limestone caves, as typical features of karst. When dolines grow and merge they form an uvala, and still larger basin-like plains are called poljes.
Reading the records and the landscape
Akiyoshidai in Mine, Yamaguchi, the largest karst plateau in Japan, is a Special Natural Monument. The Agency for Cultural Affairs notes that dolines, uvalas, poljes, karrenfeld, limestone caves and other karst features are well developed there and represent the landforms of successive stages of karst development. Mine City notes a dense group of dolines at the place called Umakorobi.
On site, look for round hollows scattered across the grassland. Some have fields or trees in their floors, and their pattern is easiest to see from higher ground.
References
- 秋吉台｜文化遺産オンライン
- https://online.bunka.go.jp/heritages/detail/173085
- 石灰岩の空洞はどうしてできるのか｜日本応用地質学会中国四国支部
- https://jseg.or.jp/chushikoku/assets/file/faq/1-07.pdf
- 秋吉台｜美祢市
- https://www2.city.mine.lg.jp/soshiki/kyoiku/hogoka/bunkazai/bunkazai/kunishitei/tokubetsu/1530.html
Last verified: 2026.09.27