Yonaguni Monument (The Mysterious Underwater Structure)

Yonaguni Monument

From Wikipedia, the free encyclopedia
Sunken formations
Yonaguni formation is located in Japan

Yonaguni formation
Location of Yonaguni formation

The Yonaguni Monument is a massive underwater rock formation off the coast of Yonaguni, the southernmost of the Ryukyu Islands, in Japan. There is a debate about whether the site is completely natural, is a natural site that has been modified, or is a manmade artifact.

The site is variably referred to as the “Yonaguni Underwater Formations” (与那国島海底地形 Yonaguni-jima Kaitei Chikei?) and the “Yonaguni Underwater Ruins” (与那国島海底遺跡 Yonaguni-jima Kaitei Iseki?) in Japanese.


The sea off Yonaguni is a popular diving location during the winter months due to its large population of hammerhead sharks. In 1987, while looking for a good place to observe the sharks, Kihachiro Aratake, a director of the Yonaguni-Cho Tourism Association, noticed some singular seabed formations resembling architectonic structures. Shortly thereafter, a group of scientists directed by Masaaki Kimura of the University of the Ryūkyūs visited the formations. Kimura is a strong advocate of the view that the formations are artificial (manmade).

The formation has since become a relatively popular attraction for divers, in spite of the strong currents. In 1997, Japanese industrialist Yasuo Watanabe sponsored an informal expedition comprising writers John Anthony West and Graham Hancock, photographer Santha Faiia, geologist Robert Schoch, a few sport divers and instructors, and a shooting crew for British Channel 4 and Discovery Channel. Another notable visitor was freediver Jacques Mayol, who wrote a book on his dives at Yonaguni. A plaque in his honor was fixed to the undersea formations after his suicide in 2001.

 Main features

The Monument consists of medium to very fine sandstones and mudstones of the Lower Miocene Yaeyama Group, deposited about 20 million years ago.[1] Most of the significant formations are connected to the underlying rock mass (as opposed to being assembled out of freestanding rocks).

The formation called “The Turtle”

The main feature (the “Monument” proper) is a rectangular formation measuring about 150 by 40 m (490 by 130 ft), and about 27 m (90 ft) tall; the top is about 5 m (16 ft) below sea level. Most of its top surface consists of a complex series of terraces and broad steps, mostly rectangular, bounded by near vertical walls.

Some of its peculiar details include:

  • Two closely spaced pillars which rise to within eight feet of the surface;
  • The “Loop Road”, a 5 m (16 ft) wide ledge that encircles the base of the formation on three sides;
  • The “Totem”, a stone column about 7 m (23 ft) tall;
  • The “Dividing Wall”, a straight wall 10 m (33 ft) long;
  • The “Gosintai”, an isolated boulder resting on a low platform;
  • The “Turtle”, a low star-shaped platform;
  • The “Triangle Pool”, a triangular depression with two large holes at its edge;
  • The “Stage”, an L-shaped rock.


 Artificial structures























The flat parallel faces, sharp edges, and mostly right angles of the formation have led many people, including many of the underwater photographers and divers that have visited the site and some scholars, to the opinion that those features are man-made. These people include Gary and Cecilia Hagland and Tom Holden who went on underwater expeditions to study and photograph the site as well as Dr. Sean Kingsley, a marine archaeologist. These features include a trench that has two internal 90° angles as well as the twin megaliths that appear to have been placed there. These megaliths have straight edges and square corners. However sea currents have been known to move large rocks on a regular basis. Some of those who see the formations as being largely natural claim that they may have been modified by human hands. The semi-regular terraces of the Monument have been compared to other examples of megalithic architecture, such as the rock-hewn terraces seen at Sacsayhuaman.The formations have also been compared to the Okinawa Tomb, a rock-hewn structure of uncertain age.


Other evidence presented by those who favor an artificial origin include the two round holes (about 2 feet wide, according to photographs) on the edge of the Triangle Pool feature, and a straight row of smaller holes which have been interpreted as an abandoned attempt to split off a section of the rock by means of wedges, as in ancient quarries. Kimura believes that he has identified traces of drawings of animals and people engraved on the rocks, including a horse-like sign that he believes resembles a character from the Kaida script. Some have also interpreted a formation on the side of one of the monuments as a crude moai-like “face”.


Supporters of artificial origin also argue that, while many of the features seen at Yonaguni are also seen in natural sandstone formations throughout the world, the concentration of so many peculiar formations in such a small area is highly unlikely. They also point to the relative absence of loose blocks on the flat areas of the formation, which would be expected if they were formed solely by natural erosion and fracturing.

If any part of the Monument was deliberately constructed or modified, that must have happened during the last Ice Age, when the sea level was much lower than it is today (e.g. 39 m (130 ft) lower around 10,000 years BCE). During the Ice Age, the East China Sea was a narrow bay opening to the ocean at today’s Tokara Gap. The Sea of Japan was an inland sea and there was no Yellow Sea; people and animals could walk into the Ryukyu peninsula from the continent. Therefore, Yonaguni was the southern end of a land bridge that connected it to Taiwan, Ryūkyū, Japan and Asia. This fact is underscored by a rock pillar in a now-submerged cave that has been interpreted as a fused stalactitestalagmite pair, which could only form above water.

Graham Hancock diving in the “Basin” at Yonaguni.


Kimura first estimated that this must be at least 10,000 years old (8,000 BCE) dating it to a time when it would have been above water.In a report given to the 21st Pacific Science Congress in 2007 he revised this estimate and dated it to 2,000 to 3,000 years ago as the sea level then was close to current levels.

The existence of an ancient stoneworking tradition at Yonaguni and other Ryukyu islands is demonstrated by some old tombs and several stone vessels of uncertain age.

 Natural formation



















Two views of the “Basin”, a pool-like structure near the apex of the main monument. It features a right-angled internal corner, sheltered by surrounding elevations.


Some of those who have studied the formation, such as geologist Robert Schoch of Boston University, state that it is most likely a natural formation, possibly used and modified by humans in the past. Schoch observes that the sandstones that make up the Yonaguni formation “contain numerous well-defined, parallel bedding planes along which the layers easily separate. The rocks of this group are also criss-crossed by numerous sets of parallel and vertical (relative to the horizontal bedding planes of the rocks) joints and fractures. Yonaguni lies in an earthquake-prone region; such earthquakes tend to fracture the rocks in a regular manner. He also observes that on the northeast coast of Yonaguni there are regular formations similar to those seen at the Monument.Schoch also believes that the “drawings” identified by Kimura are natural scratches on the rocks. This is also the view of John Anthony West.

View of the internal right-angle of the Basin. It is difficult to see how such a feature in such a protected setting could have been produced solely by natural forces such as waves or tidal action.


Patrick D. Nunn, Professor of Oceanic Geoscience at the University of the South Pacific, has studied these structures extensively and notes that the structures below the water continue in the Sanninudai slate cliffs above, which have “been fashioned solely by natural processes” and concludes in regard to the underwater structures that “there seems no reason to suppose that they are artificial.

Other examples of natural formations with flat faces and sharp straight edges are the basalt columns of the Giant’s Causeway and the natural staircase formation on Old Rag Mountain.

A series of three vertical holes run in alignment along the Basin’s straight edge. Some geologists have described them as pot-holes, which they may well be. However their direct and immediate association with another curious feature – the Basin itself – should force us to consider other possibilities as well.


Megalithic entrance tunnel leading to parallel megaliths.


Parallel megalithic blocks oriented east to west and lying at the north-west corner of the main monument.


Parallel megaliths with diver for scale.


Curious feature, close to parallel megaliths, with an apparent curving sloped stone path flanked by parallel curving walls.


Second area of terracing half a kilometre south of the main monument. Found at the base of a sheltered east-west defile and at a depth of 27 metres, it could not have been subjected to the &wave and tidal forces& that some geologists believe were responsible for the Yonaguni anomalies.


Two-ton megalith surmounting a carved platform 300 metres to the east of the main monument.


Media references

James Rollins‘ book Deep Fathom, while not explicitly mentioning the Monument, features scenes “off the coast of Yonaguni Island” involving man-made pyramid-like structures known as The Dragons that emerged above the surface after widespread seismic activity.

The Yonaguni Monument is important in Graham Hancock’s documentary Quest for the Lost Civilization.

The monument was featured on episodes of Ancient Aliens and History’s Mysteries both on The History Channel.





4 thoughts on “Yonaguni Monument (The Mysterious Underwater Structure)

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s