The Yonaguni Monument is a stepped underwater rock formation off the southern tip of Yonaguni, Japan's westernmost inhabited island, in Okinawa Prefecture about 100 km east of Taiwan. Its base lies about 25 to 26 metres down, its upper terraces rise to within a few metres of the surface, and it is cut from sandstone roughly 20 million years old. Marine geologist Masaaki Kimura argues it was shaped by people; most geologists who have examined it, including Robert Schoch of Boston University, conclude it is natural.
The site matters because it sits at the centre of the lost-civilization debate. If people carved terraces here before the sea rose, East Asian prehistory would need rewriting; if the sandstone simply breaks this way, Yonaguni shows how convincing natural geometry can look underwater. This guide sets out both cases and what has and has not been dated.
Where the Yonaguni Monument is and who found it
The formation lies just offshore below the Arakawabana cliff at the southern tip of Yonaguni, the last island in the Ryukyu chain before Taiwan. Local divers call it Iseki Point, or "Ruins Point", and it is one of Japan's best-known winter dive sites.
It was noticed in 1986 by Kihachiro Aratake, a director of the Yonaguni-Cho Tourism Association, who was scouting the waters for hammerhead sharks when he saw seabed shapes that looked architectural. A survey team from the University of the Ryukyus led by Kimura began studying the site in 1992, using scuba, sonar and underwater robots. Kimura has since made more than a hundred dives there.
By Kimura's own figures the main formation, often called the "pyramid", is a terraced mass roughly 270 metres long and 120 metres wide, its flat platforms stepping down toward the seabed in sharp-edged levels.
What Masaaki Kimura claims
Kimura, now professor emeritus at the University of the Ryukyus, where he taught from 1977 to 2002, is the main scientific voice for human construction. In his reading the main formation is a stepped monument surrounded by a complex: terraces and staircases, a loop road, retaining walls, a gate, drainage channels, a plaza and what he calls a stadium. He has also identified a turtle-shaped structure, a sphinx-like stone and a face-like rock about 7 metres tall that he compares to the moai of Easter Island. He points to what he interprets as tool marks on corners and to scratched lines he reads as rudimentary characters.
Kimura's dates have moved over time. His early work placed construction at least 10,000 years ago, when the sea was lower and the site would have been dry land, and his 1991 book Mu tairiku wa Ryukyu ni atta ("The continent of Mu was in the Ryukyus") linked the ruins to the legendary lost continent of Mu, the Pacific counterpart of Atlantis whose history is traced in our guide to Lemuria and Mu. By the time National Geographic News interviewed him in 2007 he was citing an age of at least 5,000 years, based on stalactites in submerged caves. In a report to the 21st Pacific Science Congress that same year, he proposed a much younger date of about 2,000 to 3,000 years, when sea level was close to today's, and suggested that tectonic movement later dropped the complex beneath the waves. The archaeologist Richard Pearson, a specialist in Ryukyuan prehistory, has called that revised scenario unlikely.
His reading is not the scientific consensus; it remains the position of one marine geologist and a small number of supporters.
Where the "10,000-year" figure comes from
The 10,000-year figure is an inference, not a measured date. No construction event at Yonaguni has ever been dated, and no tools, inscriptions, hearths, pottery or settlement debris have been securely associated with the formation.
The number comes from sea-level history. At the Last Glacial Maximum, about 20,000 years ago, global sea level stood roughly 120 metres lower than today, and it rose rapidly as the ice sheets melted, passing the depths of the Yonaguni base in the early Holocene. If people had shaped the rock on dry land, the argument goes, they must have done so before the water reached it. The same melt-water story underlies the debate over the Younger Dryas impact hypothesis, the cold snap that preceded the Holocene.
That reasoning only works if the rock was shaped by people in the first place, and it ignores local tectonics: the Ryukyu arc rises and sinks independently of global sea level, which is exactly why Kimura's later, younger date relies on subsidence. Kimura has cited radiocarbon dates on marine organisms growing on the rock and beryllium-10 exposure dating of the sandstone surface, but dates of that kind can at most indicate when a surface was exposed or colonized underwater. They cannot show whether a human hand shaped it.
What the rock is: the geology of the Yaeyama Group
The Yonaguni Monument is cut from medium- to very fine-grained sandstones and mudstones of the Early Miocene Yaeyama Group, laid down about 20 million years ago in shallow coastal seas. The same sandstone forms the low hills of Yonaguni itself.
Two properties of this rock explain most of what divers see. First, it is strongly bedded: it was deposited in thin layers, and those layers are separated by flat, parallel bedding planes along which the rock readily splits. Second, it is cut by joints, near-vertical fractures that run at roughly right angles to the bedding. Where flat bedding planes meet vertical joints, the rock breaks into blocks with flat tops, straight edges and right-angled corners. Stack several layers of differing hardness, let the sea strip them back one at a time, and the result is a staircase.
Yonaguni also sits in one of the most seismically active regions on Earth, near the junction of the Ryukyu arc and Taiwan. Repeated earthquakes keep opening the joints, and powerful currents and storm waves carry away the broken pieces. That is why the terraces can look swept clean, a point both sides of the debate return to.
Why most geologists say it is natural
The geologists who have dived the site have mostly concluded that the Yonaguni Monument is a natural formation. Robert Schoch of Boston University made a number of dives there in the late 1990s and sampled the rock. He describes the sandstone as having "numerous well-defined, parallel bedding planes along which the layers easily separate", combined with vertical joints, and told National Geographic News that the straight edges are "basic geology and classic stratigraphy". In his assessment the "walls" are platforms that tilted as softer rock eroded beneath them, the "roads" are erosion channels, the "post holes" are the work of eddies and marine organisms, and the markings read as writing are natural scratches. He also stresses that the structure is solid bedrock, with no separately placed blocks. Schoch has allowed that people may have used or modified parts of the outcrop, but regards it as overwhelmingly natural.
The writer John Anthony West, who dived with Schoch and later described the trip in "Diving for Lemuria" (1998), came to the same view and said Kimura had not looked carefully enough at the natural processes at work. That is notable, because West and Schoch are best known for arguing that the Great Sphinx is far older than Egyptologists accept.
The German geologist Wolf Wichmann studied the formation in 1999, on an expedition for Spiegel TV, and again in 2001 at the invitation of Graham Hancock; he found natural processes sufficient to explain it. A geosite study of Yonaguni by Takayuki Ogata and colleagues, published in the Japanese journal E-journal GEO in 2020, used a digital elevation model and fieldwork at three coastal sites to conclude that the monument, however artificial it looks, is a natural feature shaped by weathering and erosion along bedding and joints.
The comparison sites are the strongest argument. Very similar right-angled steps occur on land at Sanninudai and elsewhere along Yonaguni's coast, where they can be walked and inspected. Patrick Nunn, a geoscientist who has written widely on Pacific sunken-land legends, treats those step-like formations as purely natural.
What still looks engineered, and the case for a closer look
Supporters of an artificial origin make several points that deserve a fair hearing. The concentration of flat platforms, straight channels and right-angled steps in one small area is striking, and photographs of the main terrace look strongly architectural. Graham Hancock, whose book Underworld (2002) brought Yonaguni to a wide audience as a possible relic of an Ice Age culture drowned by rising seas, argues that so many peculiar features in one place is unlikely by chance, and that the relative absence of loose blocks on some flat areas is hard to explain if the rock simply fractured in place. Kimura adds the features he reads as faces, carvings and tool marks.
Geologists answer that the clustering is what you would expect from one uniform rock unit with one joint pattern, that currents remove debris, and that photographs flatten an irregular surface into cleaner lines than divers see in person. Schoch has said the site is "not as regular as many people claim". Even so, a full, published archaeological survey with systematic excavation of the surrounding seabed has never been carried out, and that gap keeps the question open for many readers. The honest summary is that nothing found so far requires a human builder, but the site has not been studied as thoroughly as its fame would suggest.
Is Yonaguni recognized as a cultural site?
No. Neither Japan's Agency for Cultural Affairs nor the Okinawa Prefecture government recognizes the Yonaguni Monument as a cultural property, and neither has researched or protected it as one. Kimura says he reported it to the prefectural board of education in 1998 without any protection measures following. That reflects heritage officials who are not persuaded it is man-made, not concealment: the site is openly promoted to divers and tourists.
Yonaguni is often listed alongside other submerged "pyramids", such as the Azores seamount discussed in our earlier post on a supposed 20,000-year-old underwater pyramid in the Atlantic, and it appears in the blog's roundup of the most mysterious archaeological discoveries.
Billy Carson's reading
Billy Carson has not published a dedicated video or episode on Yonaguni, and no specific claim about the formation is attributed to him here. His framework for lost civilizations is set out elsewhere. His documented position, explained in our guide to Atlantis and the Anunnaki connection, is that Atlantis was a real, technologically advanced pre-flood civilization tied to the Anunnaki of the Sumerian and Babylonian texts, and that its survivors seeded the ancient cultures that appear fully formed in the archaeological record. Shared features such as stepped pyramids and flood stories are, in his reading, the traces of one dispersed parent culture.
Drowned sites like Yonaguni raise the questions that argument turns on: what lay on the coastlines the post-glacial seas swallowed, and what memories of those losses survive in myth. The evidence at Yonaguni itself has to be weighed on its own terms, and on present evidence it does not settle the matter either way. The wider Anunnaki thread is gathered in the Anunnaki topic hub.
Watch, read and go deeper
The nearest long-form listening on 4BK TV is the stream "Sunken Cities, Ancient Wars, and Catastrophes" on the 4biddenknowledge Podcast show, which sits within the broader sunken-cities conversation. For the lost-continent background that Kimura drew on, read Lemuria and Mu explained. To compare Yonaguni with a Pacific site that is unquestionably human-built, read the Nan Madol guide, where radiocarbon dates and quarry sourcing tell a clear story. The Anunnaki topic hub connects these sites to the texts at the centre of Carson's work.
Frequently asked questions
Is the Yonaguni Monument man-made?
It has not been shown to be. Masaaki Kimura of the University of the Ryukyus argues it was shaped by people, but geologists including Robert Schoch and Wolf Wichmann, and a 2020 study by Takayuki Ogata and colleagues, conclude it formed naturally as sandstone split along bedding planes and joints. No tools, inscriptions or settlement remains have been securely linked to it.
How old is the Yonaguni Monument?
The rock itself is about 20 million years old, part of the Early Miocene Yaeyama Group. No date for any human shaping has ever been measured. Kimura first proposed at least 10,000 years, based on when rising seas would have covered it, and later suggested 2,000 to 3,000 years with tectonic sinking; neither is a measured construction date.
How deep is the Yonaguni Monument?
The base of the main formation lies about 25 to 26 metres below the surface, and its upper terraces rise to within a few metres of it. The site sits off the southern tip of Yonaguni, below the Arakawabana cliff, and is a popular winter dive with strong currents.
Is Yonaguni connected to the lost continent of Mu?
Kimura linked the formation to Mu in his 1991 book, but Mu itself traces back to nineteenth-century writers such as Augustus Le Plongeon and James Churchward, not to ancient sources, and marine geology finds no sunken continent in the Pacific. The idea's history is covered in our Lemuria and Mu guide.
Can you visit the Yonaguni Monument?
Yes. It is an established dive site reached by boat, best known in winter when hammerhead sharks gather, and its strong currents suit experienced divers. It is not a designated cultural property, so access is not restricted on heritage grounds.
Sources and further reading
- Masaaki Kimura, Mu tairiku wa Ryukyu ni atta (Tokuma Shoten, 1991), and "Ancient Megalithic Construction Beneath the Sea off Ryukyu Islands in Japan", Proceedings of Oceans '04 MTS/IEEE Techno-Ocean '04 (2004)
- Robert M. Schoch, "Yonaguni Enigmatic Underwater Monuments" (1999)
- John Anthony West, "Diving for Lemuria" (1998)
- Julian Ryall, "Japan's Ancient Underwater 'Pyramid' Mystifies Scholars", National Geographic News (September 2007)
- Takayuki Ogata, Makoto Otsubo and Hideyuki Ito, "Geosites of Yonaguni Island", E-journal GEO 15(1) (2020)
- Patrick D. Nunn, Vanished Islands and Hidden Continents of the Pacific (University of Hawai'i Press, 2009)
- Graham Hancock, Underworld: Flooded Kingdoms of the Ice Age (2002)
