But now it can't be seen from land at all.
"There is a possibility that the islet has been eroded by wind and snow and, as a result, disappeared," senior coast guard official Tomoo Fujii told the Asahi Shimbun newspaper.
A coast guard official also told Agence France-Presse that the disappearance "may affect Japan's territorial waters a tiny bit . . . if you conduct precision surveys."
Land disappearances are not unheard of. A study published in Environmental Research Letters in 2016, for example, found that five reef islands in the Pacific Ocean's Solomon Islands had disappeared between 1947 and 2014. That study determined that although sea-level rise has caused erosion in the central Pacific, research in the western Pacific found that "extreme events, sea walls and inappropriate development" were likely responsible for the majority of shoreline changes in that region.
For its part, Japan has taken measures to ensure it lays claim to certain islands to avoid further territorial disputes with its neighbors.
In 2016, Japan announced it would spend $107 million to rebuild the observatory tower on a Pacific island called Okinotorishima, which is about 1,000 miles south of the capital Tokyo.
The Guardian reported at the time that Beijing had claimed the island was made of only rocks and thus disqualified Japan from including it in its exclusive economic zone. A United Nations convention claimed that "rocks which cannot sustain human habitation or economic life of their own" don't qualify for such a zone.