The case in 60 seconds
The Yonaguni formation looks remarkably geometric. But “looking geometric” does not, by itself, establish that something is human-made.
The main formation measures approximately 100 × 60 metres and stands about 25 metres high. It contains large flat surfaces, terraces, steep edges and step-like fractures.
The local geology has precisely the characteristics that can produce such shapes naturally: Miocene sandstones are widespread on Yonaguni, and the rocks contain numerous joints, fractures and faults. A 2020 geomorphological study documents pronounced joint systems and erosion forms on the island's rock surfaces; new submarine geomorphological research in 2024 also examines sandstone erosion forms around Yonaguni using multibeam sonar, ROV photogrammetry and diving.
The strongest advocate of a human-made interpretation is Masaaki Kimura of the University of the Ryukyus. Kimura interpreted the formation as a complex built or worked about 10,000 years ago, when it was on land. Geologist Robert Schoch, by contrast, concluded that it was largely natural, although ancient people might have used or modified parts of it.
The claim
“Yonaguni is a pyramid or temple complex of a lost civilisation more than 10,000 years old, submerged at the end of the last Ice Age.”
This claim links two different propositions: that the formation was once above sea level and that people built it. The first is palaeogeographically possible; the second requires separate archaeological evidence.
What we know
The evidence
1 — The strongest point of the natural explanation: how does the rock break?
Yonaguni sandstone can separate along horizontal bedding and vertical joint systems. Together, these directions can produce steep walls, broad flat platforms and a “step” appearance. Fieldwork published in 2020 reported numerous joints and normal faults developed under horizontal stresses in the island's Sanninu-dai area.
Strong support for the natural model2 — Similar angular forms occur on land on the same island
This comparison is crucial. If the same rock unit produces flat surfaces, steep edges, terrace-like platforms and fractured blocks onshore and along the coast, the underwater geometry need not require human workmanship. This is also Robert Schoch's central field argument.
Comparative geology3 — Kimura's human-made interpretation is a genuine academic proposal
Combining submarine geological/geophysical research, diving observations and Ryukyu palaeogeography, Masaaki Kimura interpreted the Yonaguni formation as a human-made complex 6,000–10,000+ years old. His 2003 paper described it as a large gusuku-like structure.
This does not mean that “scientists have proven it is human-made”. It is a published interpretation on one side of the debate.
A genuine academic view, not a consensus4 — The critical gap: definite traces of human workmanship
Evidence strongly supporting an architectural-complex interpretation would include repeated tool marks, quarrying traces, masonry, mortar, human-made fill, a reliable cultural layer, or datable archaeological material directly associated with the structure. None has been demonstrated for Yonaguni's main formation in a generally accepted way.
The central weakness of the human-made hypothesis5 — “It was on land 10,000 years ago” ≠ “It was built 10,000 years ago”
Global sea-level rise after the last Ice Age makes it plausible that some coastal areas now in shallow water were once dry land. Kimura's palaeogeographic studies discuss the progressive submergence of the Ryukyu region. A rock being on land at that time, however, does not establish that people made it.
A crucial distinction6 — Research in 2024 still focuses on geomorphology
Work presented in 2024 by teams from Kyushu University and other Japanese research institutions examined submarine sandstone erosion forms around Yonaguni using multibeam sonar, ROV photogrammetry and SCUBA surveys. This shows that the site remains a subject of serious geomorphological research.
Current scientific contextTimeline
The Yaeyama Group sandstones making up much of Yonaguni are formed.
Sea level is lower than today; some parts of the present coast are dry land.
Rising sea level progressively submerges the coastal landscape.
Kihachiro Aratake discovers the main underwater formation.
Masaaki Kimura develops the human-made-complex interpretation; international interest grows.
Kimura argues for his Ryukyu palaeogeographic and human-made Yonaguni interpretations in academic publications.
A study of Yonaguni's onshore geomorphology details its sandstones, faults, joints and erosion forms.
New sonar, ROV photogrammetry and diving surveys focus on submarine sandstone erosion forms.
Theories
Theory A — An entirely natural rock formation
Strength: Sandstone bedding, joint systems, faulting and marine erosion can explain the broad flat surfaces and steep steps. Similar shapes also occur on land on the island.
Weakness: Some details—particularly combinations of regular terraces—look unusually “architectural” at first sight. Visual intuition is not evidence, but keeps the question alive.
Theory B — A natural formation partly modified by people
Strength: An intermediate model also adopted by Robert Schoch. Ancient people could theoretically have used the natural rock surface as steps, a passage or a ritual area, or made small alterations.
Weakness: There are still no indisputable tool marks or cultural layers reliably demonstrating such “touch-ups”.
Theory C — An entirely human-made ancient monument
Strength: The platforms, steps, passages and some surrounding forms described by Kimura suggest an architectural plan. Lower past sea levels make human access chronologically possible.
Weakness: “People could reach it” is different from “people built it”. Definite construction techniques, tool marks, archaeological culture and datable building material have not been demonstrated.
Theory D — Mu / Atlantis / a lost advanced civilisation
Strength: It provides a powerful popular-cultural narrative.
Weakness: No independent archaeological, written or technological evidence links Yonaguni with Mu or Atlantis.
Viral claims: are they true?
| Claim | Assessment | Why? |
|---|---|---|
| “It is definitely a 10,000-year-old pyramid.” | Not established | The roughly 10,000-year human-made interpretation is Kimura's proposal; it has not been independently verified as a construction date. |
| “Scientists say it cannot be natural.” | False | The geological explanation is strong; geologists who have examined the site include advocates of a natural or mostly natural interpretation. |
| “Nature cannot make stairs at 90 degrees.” | Faulty reasoning | Approximately right angles can form through natural fracturing in jointed, layered rock. |
| “Hieroglyphs have been found on it.” | Disputed / weak | Various scratches and shapes have been interpreted as writing or symbols, but there is no generally accepted epigraphic reading. |
| “A city, roads and stadium complex have been found.” | An interpretation | These names rely on Kimura's morphological interpretations, not independently verified architectural functions. |
| “Sea level rose, so an ancient civilisation definitely sank.” | An invalid inference | Ancient coasts really were submerged, but the conclusion that a monumental civilisation occupied them requires separate evidence. |
What remains unknown
My assessment
🟡 It looks highly “artificial”; the weight of evidence favours a natural formation.
Yonaguni's greatest trap is visual intuition. Steps, flat surfaces and steep corners immediately suggest “architecture” to us. Yet geology—particularly horizontally bedded, vertically jointed sandstone—can produce strikingly geometric surfaces. Yonaguni's onshore geology directly demonstrates this mechanism.
The current evidence is therefore insufficient for the entirely human-made lost city/pyramid hypothesis. I nevertheless do not assign the case 🟢, because the narrower possibility of people using or locally modifying a natural formation has not been fully closed archaeologically.
The best working hypothesis is therefore: the main mass is natural; possible human use or small-scale intervention merits investigation.
References
Popular “Atlantis/Mu” accounts were not used as evidence. The main framework compares geology, palaeogeography and the published human-made interpretation.
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Schoch – Yonaguni
Last updated: 6 October 2026.