Discovery & Location
The Yonaguni Monument is a massive underwater rock formation located off the southern coast of Yonaguni Island, the westernmost inhabited island of Japan. Discovered in 1987 by local dive tour operator Kihachiro Aratake, the formation features what appear to be terraced platforms, right angles, and smooth surfaces that have sparked intense debate about whether it is a natural geological formation or a human-made structure submerged by rising sea levels at the end of the last Ice Age.
Site Specifications
- Location: 24°26'N, 123°0'E, off southern coast of Yonaguni Island
- Distance from Shore: Approximately 100 meters offshore
- Depth: 5 to 40 meters below sea level
- Main Feature Dimensions: Approximately 150m long × 40m wide
- Highest Point: About 5 meters below surface
- Discovery Date: 1987 by Kihachiro Aratake
- Geology: Fine sandstone and mudstone of the Yaeyama Group (Early Miocene, ~20 million years old rock formation)
Discovery Story
Kihachiro Aratake, a local dive tour operator, discovered the formation while searching for new dive sites to observe hammerhead sharks:
- Date: 1987 (exact date uncertain)
- Circumstances: Aratake was exploring waters off Yonaguni for shark diving sites
- Initial Impression: Believed he had found an artificial structure due to apparent geometric features
- Public Announcement: News spread in diving and then mainstream media
- Academic Interest: Discovery attracted geologists, archaeologists, and alternative researchers
Location Context
Yonaguni Island
- Position: Westernmost island of Japan, closer to Taiwan (108 km) than main Japanese islands
- Population: ~1,700 inhabitants
- Known History: Inhabited for at least 2,000 years, part of Ryukyu Kingdom (15th-19th centuries)
- Archaeology: No known ancient megalithic construction in local archaeological record
- Geology: Island composed of sedimentary rock formations prone to fracturing
Description of Features
The Main Monument
The largest and most studied formation exhibits several striking features:
Main Feature Characteristics
Platform or Terrace:
- Large flat top surface approximately 150m × 40m
- Appears to be leveled or naturally flat
- Regular height differences suggest terraces or steps
Vertical Walls:
- Near-vertical faces on multiple sides
- Walls meet at approximately 90-degree angles
- Heights ranging from 2-10 meters
Stepped Structures:
- Series of step-like formations
- Some appear remarkably regular in height and depth
- Largest "steps" approximately 1-2 meters in height
"The Road":
- Flat pathway approximately 5 meters wide
- Runs along base of main structure
- Appears suspiciously uniform in width
Additional Features
| Feature Name |
Description |
Artificial Arguments |
Natural Explanation |
| "The Stadium" |
Semi-circular depression adjacent to main structure |
Regular shape suggests excavation |
Natural erosion basin in softer rock layers |
| "The Turtle" |
Oval rock formation resembling turtle |
Zoomorphic carving? |
Erosion of rounded rock formation |
| "The Gateway" |
Narrow passage through rock |
Intentional doorway? |
Natural joint or fracture widened by erosion |
| "Pillars" or "Columns" |
Upright rock formations |
Structural supports? |
Erosion-resistant rock cores remaining after softer material eroded |
| "The Triangle" |
Triangular cutout in rock face |
Carved symbol or niche? |
V-shaped joint or fracture |
Measurements & Angles
Geometric Analysis (Kimura Measurements)
- Right Angles: Multiple intersections of planes at ~90 degrees (±5°)
- Parallel Lines: Some edges appear parallel over 10+ meter distances
- Step Regularity: Step heights vary but some series show consistent ~1m risers
- Flat Surfaces: Top platform relatively flat (±50cm variation over large area)
- Face Orientations: Main faces oriented roughly cardinal directions (±15-20°)
Masaaki Kimura's Research (Artificial Hypothesis)
Professor Kimura's Investigation
Masaaki Kimura, marine seismologist at Ryukyu University, has conducted the most extensive investigations arguing for artificial origin:
Kimura's Artificial Structure Theory
Human-Made Monument (10,000-5,000 years old)
Background:
- Credentials: Professor of Marine Seismology, Ryukyu University (now emeritus)
- Research Period: 1992-present (30+ years)
- Dive Count: Made over 100 dives to site
- Methodology: Detailed measurements, photographs, drawings, comparisons
Evidence Cited for Artificial Origin:
- Tool Marks: Claims to have identified marks consistent with stone tools
- Regularity: Right angles, parallel lines, uniform steps exceed natural variation
- Missing Debris: Absence of fallen blocks where "carved" material should be
- Deliberate Shaping: Features arranged in deliberate patterns
- Stone Holes: Claims circular holes are quarrying marks or postholes
- Carved Symbols: Interprets some features as carved animals or symbols (highly disputed)
- Comparison Sites: Similarities to castle walls and other structures in Okinawa region
Proposed Dating:
- Submersion Date: Must predate sea level rise that submerged it
- Sea Level History: Waters were ~40-100m lower during last Ice Age (ended ~12,000 years ago)
- Kimura's Estimate: Structure built 10,000-2,000 years ago when site was above sea level
- Problem: No known civilization in region with megalithic building capability in this period
Cultural Attribution:
- Kimura suggests connection to ancient Ryukyuan people
- Possibly related to Jomon culture of ancient Japan (14,000-300 BCE)
- However, no Jomon megalithic architecture known from archaeological record
Kimura, M. (2004). "Diving survey of underwater ruins off Yonaguni Island, Ryukyu Islands, Japan." Marine Technology Society Journal, 38(4), 92-108. [Kimura's published research]
Kimura's Reconstructed Map
Kimura created detailed maps interpreting the formation as a deliberate structure:
- Identifies main pyramid-like structure
- Labels various features as "gates," "roads," "plazas," "staircases"
- Proposes it was a religious or ceremonial complex
- Suggests it may be one of multiple submerged sites in region
Robert Schoch's Geological Analysis (Natural Hypothesis)
Dr. Schoch's Investigation
Robert Schoch, Ph.D. in geology from Yale and Associate Professor of Natural Sciences at Boston University, conducted geological analysis of Yonaguni:
Schoch's Natural Formation Theory
Naturally Fractured Sandstone
Background:
- Credentials: Ph.D. Geology (Yale), specialization in erosion and weathering
- Site Visits: Multiple dives to Yonaguni in 1997, 1998, 2000
- Methodology: Geological analysis of rock type, fracture patterns, erosion mechanisms
- Context: Also known for Sphinx water erosion hypothesis - not dismissive of alternative theories
Geological Explanation:
1. Rock Type and Fracture Properties:
- Lithology: Fine-grained sandstone and mudstone (Yaeyama Group)
- Bedding Planes: Horizontal sedimentary layers create natural flat surfaces
- Joint Sets: Vertical fractures (joints) oriented roughly perpendicular to bedding
- Natural Geometry: Intersection of horizontal bedding and vertical joints naturally creates right angles and rectangular blocks
2. Regional Comparison:
- Nearby Formations: Schoch documented similar formations above sea level on Yonaguni Island itself
- Identical Geometry: Above-water formations show same right angles, terraces, and steps - clearly natural
- Same Rock Unit: Both underwater and above-water formations are same geological formation
- Key Argument: If identical features on land are natural, underwater features likely natural too
3. Sandstone Fracture Mechanics:
- Joint Spacing: Regular joint spacing is normal in sandstone (controlled by rock mechanical properties)
- Orthogonal Joints: Two perpendicular joint sets are common in sandstone worldwide
- Erosion Along Joints: Water erosion preferentially exploits joints, widening them to create vertical walls
- Block Removal: Joint-bounded blocks fall away, creating terraces and steps
4. Missing Evidence of Human Work:
- No Artifacts: No tools, pottery, or other artifacts found at site
- No Tool Marks: Schoch saw no convincing evidence of tool marks under magnification
- Debris Present: Contrary to Kimura, Schoch noted debris blocks scattered around base (consistent with natural collapse)
- No Quarry Marks: Features interpreted as "quarry marks" by Kimura appear to be natural bore holes from marine organisms or weathering pits
- Roughness: Surfaces relatively rough, not smoothed as would be expected from human work
5. Similar Natural Formations Worldwide:
- Giant's Causeway (Ireland): Hexagonal basalt columns from natural cooling fractures
- Devil's Postpile (California): Similar geometric columns, entirely natural
- Numerous Sandstone Formations: Rectangular jointing common in sandstone globally
Schoch, R. M., & McNally, R. A. (2003). "Voices of the Rocks: A Scientist Looks at Catastrophes and Ancient Civilizations." New York: Harmony Books. [Includes Yonaguni analysis]
Schoch, R. M. (1999). "An Enigma in Stone." The Japan Times (October 2, 1999). [Popular article on findings]
Schoch's Conclusion
Primarily Natural with Possible Minor Modifications
Schoch's final assessment:
- Main Formation: Overwhelmingly natural geological formation
- Possible Human Touch: Cannot rule out that ancient people may have slightly modified some natural features (made steps more regular, carved a few symbols)
- Not a Building: Does not represent a constructed building or monument
- Analogy: Like a natural rock formation that ancient people may have regarded as sacred and minimally altered
- Further Study: Underwater archaeology should continue, but expectations should be realistic
Sea Level & Dating Implications
Post-Glacial Sea Level Rise
If Yonaguni Monument were human-made, dating is constrained by sea level history:
Sea Level Timeline
- Last Glacial Maximum (~20,000 years ago): Sea level ~120-130 meters lower than present
- Yonaguni Site (~40m depth): Would have been above water until ~10,000-8,000 years ago
- Rapid Rise Period (15,000-8,000 BP): Sea level rose quickly as glaciers melted
- Slower Rise (8,000-3,000 BP): Continued rising to near-modern levels
- Implication: Any human construction would need to date to >8,000-10,000 years ago
Archaeological Context Problems
The required age creates significant archaeological problems:
- No Megalithic Tradition: No known megalithic construction in Japan or region before 500 CE
- Jomon Culture (14,000-300 BCE): Primary culture in Japan during relevant period
- Known for sophisticated pottery (oldest in world)
- Hunter-gatherer-fisher lifestyle
- No monumental stone architecture known
- Lived in pit houses, not stone structures
- Regional Context: No comparable structures in East Asia from this period
- Technology Gap: Quarrying and transporting large stones requires technology not evidenced in Jomon record
Alternative Dating Scenarios
More Recent Construction?
Post-Submersion Dive Construction
Some have suggested structure could have been built underwater by breath-hold divers from Okinawan culture (~2,000 years ago):
Problems:
- Quarrying and shaping stone underwater is exponentially more difficult than on land
- No evidence of underwater construction technology in historical Okinawa
- Scale and precision would be extraordinary achievement even on land
- No historical records or oral traditions of such a project
Other Expert Opinions
Japanese Archaeologists
Mainstream Japanese archaeology has been largely skeptical:
- Agency for Cultural Affairs: Has not designated site as archaeological monument
- Okinawa Prefectural Board of Education: No official recognition as archaeological site
- Academic Conferences: Limited serious archaeological discussion in Japanese journals
- Consensus: Most Japanese archaeologists agree with geological explanation
Alternative Researchers
- Graham Hancock: Presented Yonaguni as possible evidence of pre-flood civilization
- John Anthony West: Suggested connection to ancient advanced civilization
- Robert Bauval: Investigated site, maintains open mind but acknowledges geological arguments
- Documentary Coverage: Featured in various documentaries presenting artificial hypothesis
Underwater Archaeologists
Few underwater archaeologists have seriously investigated as potential archaeological site because:
- Geological explanation accounts for observations without requiring human intervention
- Absence of artifacts, tool marks, or associated cultural materials
- Limited research funding for what appears to be natural formation
- Preference to focus resources on confirmed archaeological sites
Multiple Interpretations
Geological Consensus
Natural Sandstone Formation
Summary: The Yonaguni Monument is a natural geological formation created by the fracturing and erosion of bedded sandstone and mudstone. Horizontal bedding planes and two perpendicular sets of vertical joints naturally create the right angles, terraces, and geometric appearance. Identical formations exist above sea level on Yonaguni Island, demonstrating the natural origin.
Key Proponents: Robert Schoch, most geologists who have examined the site
Evidence:
- Rock type (fine sandstone) prone to rectangular fracture
- Identical features visible in above-water formations nearby (clearly natural)
- Fracture patterns consistent with sandstone geology worldwide
- Absence of artifacts, tool marks, or cultural materials
- Presence of scattered debris blocks (from natural collapse)
- No comparable human-made structures from required time period
Artificial Structure Hypothesis
Human-Modified or Constructed Monument
Summary: The formation was intentionally quarried, shaped, and constructed by an unknown ancient civilization before being submerged by post-glacial sea level rise approximately 10,000-8,000 years ago.
Key Proponent: Masaaki Kimura
Evidence Cited:
- Regularity of right angles and terraces exceeds typical natural variation
- Alleged tool marks and quarrying evidence
- Stepped features arranged in deliberate patterns
- Possible carved symbols (turtle, etc.)
- Overall arrangement suggests deliberate design
Problems:
- No artifacts or clear human modification evidence
- No known civilization with required capabilities in region/period
- Geological explanation accounts for all features
- Above-water analog formations are clearly natural
Middle Ground Position
Natural Formation with Minor Human Modification
Summary: Primarily natural formation that ancient people discovered, regarded as sacred, and minimally modified (enhanced steps, carved symbols).
Proponents: Robert Schoch allows this possibility, some Japanese researchers
Logic:
- Main structure is natural
- Ancient people may have enhanced natural features
- Analogous to rock-cut temples elsewhere that modify natural formations
- Would not require advanced civilization, just local enhancement
- Evidence insufficient to confirm, but cannot rule out minor human touch
Key References
Kimura, M. (2004). "Diving survey of underwater ruins off Yonaguni Island, Ryukyu Islands, Japan." Marine Technology Society Journal, 38(4), 92-108. [Kimura's artificial structure argument]
Schoch, R. M., & McNally, R. A. (2003). "Voices of the Rocks: A Scientist Looks at Catastrophes and Ancient Civilizations." New York: Harmony Books. [Includes Yonaguni geological analysis]
Schoch, R. M. (1999). "An Enigma in Stone." The Japan Times, October 2, 1999. [Accessible summary of geological position]
Hancock, G. (2002). "Underworld: The Mysterious Origins of Civilization." New York: Crown. [Alternative perspective]