A Strange Discovery Beneath the Sea Near Japan’s Western Edge
Off the coast of Yonaguni Island, Japan’s southernmost inhabited island, a massive underwater rock formation lies beneath clear coastal waters about 100 kilometers east of Taiwan. First noticed in 1986 by local diver Kihachiro Aratake, the structure immediately stood out. Flat terraces, sharp angles, and step like features were visible on the seafloor, unlike anything commonly seen by divers in the area. Aratake reported the find to researchers, and within months scientists began visiting the site, which became known as the Yonaguni Monument.
Location and Geological Setting of the Yonaguni Monument
The formation lies below the Arakawabana cliff at the southern tip of Yonaguni Island, oriented south southeast. It consists of medium to very fine sandstone and mudstone belonging to the Lower Miocene Yaeyama Group. These rocks are believed to have formed around 20 million years ago. Most of the structure remains attached to the surrounding bedrock rather than being composed of separate blocks. The area is known for strong ocean currents and frequent seismic activity, both of which affect exposed rock formations over long periods.
Scientific Explanations and Geological Studies
Marine geologist Masaaki Kimura of the University of the Ryukyus studied the site extensively and argued that the features were carved by human hands. He described stepped monoliths and claimed to identify shapes resembling roads, walls, and platforms. His conclusions were challenged by many geologists. Robert Schoch examined the site and noted extensive parallel bedding planes and vertical joints typical of natural sandstone formations. He observed similar formations on land along Yonaguni’s coast. German geologist Wolf Wichmann also studied the site in 1999 and 2001 and concluded that natural processes could explain the structure.
In 2019, Takayuki Ogata and other researchers conducted digital elevation modeling and field studies at multiple Yonaguni geosites. Their analysis found that the monument’s shapes matched erosion patterns caused by weathering along bedding planes and fractures. Comparable formations were documented at the Sanninudai geosite onshore.
Disputes Over Human Construction Claims
Kimura initially proposed that the formation dated back at least 10,000 years, later revising the estimate to 2,000 to 3,000 years. He suggested tectonic movement submerged the structure after construction. He also connected the site to Mu and the Yamatai culture. Archaeologists such as Richard J. Pearson rejected these ideas. Japanese government agencies have not classified the site as a cultural artifact and have not conducted preservation work. Today, the Yonaguni Monument remains an underwater formation studied primarily through geological research and diving exploration.
