Between 1950 and 1980, about half of Yokoshima Island disappeared beneath the East China Sea. The island lies about 1 km off the coast of Nagasaki and was mined for coal during the late 19th and early 20th centuries. We analyzed the geology of the island and surrounding seafloor to investigate how it became submerged. Two low-cost techniques were used to view underwater structures: a commercial drone fitted with a video camera in waters shallower than 5 m and an echo sounder and side-scan sonar system designed for amateur fishers in waters deeper than 5 m. We showed that the partial submergence of the island could be interpreted as a result of subsidence. Subsidence and northward tilting of sedimentary rocks north of the island, probably caused by collapse of abandoned subsea mine workings, created an extensional regime south of the island that led to the formation of steep cliffs and collapse of the southern side of the island. Our study also shows that low-cost commercially available technology can be used for rapid scientific investigations in shallow water areas.

在1950年至1980年之间，横岛岛约有一半消失在东海下方。该岛位于长崎海岸附近约1公里处，在19世纪末至20世纪初被开采为煤炭。我们分析了岛屿和周围海底的地质状况，以研究其如何被淹没。两种低成本的技术被用于观察水下结构：在低于5 m的水域中装有视频摄像机的商用无人机，以及为在5 m以上的水域中的业余渔民设计的回声测深仪和侧扫声纳系统。我们表明，该岛的部分淹没可以解释为沉降的结果。该岛北部沉积岩的沉陷和向北倾斜，可能是由于废弃的海底矿山开采塌陷造成的，在该岛以南建立了一个扩张政权，导致陡峭的悬崖形成和该岛南侧的倒塌。我们的研究还表明，低成本的商用技术可用于浅水区的快速科学研究。