Yonaguni Monument

A submerged sandstone formation off Yonaguni Island, Japan, marked by broad terraces and sharp edges. Whether its shapes are natural or partly human-made remains disputed.

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Masaaki Kimura: A Japanese marine geologist who argues that the Yonaguni formation includes structures shaped by humans. His interpretation is the most prominent case for ancient construction at the site.
Yonaguni Island: The westernmost inhabited island of Japan, located in the Yaeyama Islands near Taiwan. The formation lies off this island’s southern coast.
Sandstone: A sedimentary rock composed mainly of sand-sized mineral or rock fragments cemented together. The formation consists largely of sandstone, which can split along natural planes.
Kihachiro Aratake: A Japanese dive operator credited with discovering the submerged formation off Yonaguni Island in 1986. His discovery brought the formation to wider attention.
Robert Schoch: An American geologist known for arguing that the Yonaguni formation is naturally fractured sandstone. His geological interpretation challenges claims that the terraces are human-built.
Iseki Point: A coastal headland on Yonaguni Island near the submerged rock formation commonly called the Yonaguni Monument. The formation is located offshore from this part of the island.
Sedimentary rock: Rock formed from accumulated sediment that has been compacted or cemented. Its layered structure helps explain how broad ledges may develop without construction.
Ryukyu Islands: An island chain extending southwest from Kyushu, Japan, toward Taiwan. Yonaguni belongs to this island chain and shares its regional geological setting.
Tafoni: Cavities and honeycomb-like features formed in rock by weathering processes, especially salt weathering. Weathering features offer natural explanations for some of the formation’s sharp-edged shapes.
Yonaguni underwater ruins: The submerged terraces, ledges, and block-like features on the seabed off Yonaguni Island. This name emphasizes the formation’s appearance without resolving its origin.