Poor Knights marine reserve
the deep sea of Rikoriko Cave
by Dr J Floor Anthoni (2007)

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Rikoriko Cave Fact Sheet

Where is this sea cave?
Two large islands and many smaller islets make up the group of islands that are The Poor Knights Islands.
Their land area is just over 200 hectares, and they lie 12 nautical miles of the North East coast of Tutukaka with co-ordinates latitude 35 28';South and 174 44'; East.

The southern island is called Aorangi has a conical shape with its peak reached at 254 metres.

Rikoriko Cave is in Maroro Bay in the north west side of the island.

How did this cave form?
10 million years ago the volcano that created these islands was 25 km in diameter and stood 1000 metres above the surrounding landscape.

An eruption formed a giant gas bubble that became Rikoriko Cave

How do we know it is the biggest in the world?
Using a sophisticated 3D laser scanner for the above water section of the cave, and traditional hydrographic surveying techniques for the seafloor, above and below water models were calculated as well as a volume for combined surface.

The survey of Rikoriko in itself was significant in setting a standard for accuracy and mathematical analysis that might be applied elsewhere in the world.

Its calculated volume is 221 494 cubic metres ( or 7.8 million cubic feet).
This is over twice the volume of two other known sea caves that claim biggest status.

What are the figures?
The sea surface inside is roughly a hectare.

The cave is 130 metres long, a depth below water of 26 metres, and a height to the ceiling above water of 35 metres, and a width of 80 metres.

A Guinness Book of World Records claim has been lodged.

Rikoriko Cave Chronicles.

    *      In the Second World War a Japanese submarine tucked away inside the cave and stopped for two weeks whilst undergoing repairs.

    *      Rikoriko means waning light in Maori, or twilight.

    *      There is plant life in the cave that is different from anywhere else. There are ferns hanging from the ceiling that only receive light for photosynthesis from sunlight coming in the entrance and bouncing off the water surface up to the roof.

    *      At the rear of the cave there is an underwater cup coral that normally grows at depths of 200 metres. The amount of light that reaches the coral, tricks it into thinking it is deeper than it is, so it grows at about 10-15 metres.

    *      The under water life out at the Poor Knights is very lush and the kelp is deeply forested. Inside the cave however, there is no kelp growing at all. The seascape is very stark and moon like.

    *      The visibility is intense and lucid. Visibility underwater is measured in the distance that you can see horizontally through the water. Normal conditions at the Poor Knights can give us between 15 and 25 metres, but inside Rikoriko we often get 35-45 metres visibility.

    *      The cave is renown for its amazing acoustics Twenty years ago TVNZ Wild South were filming “Deep Blue” and Herbs played their music inside the cave.

    *      Wade Doak had submerged audio mikes in the water transmitting live sound, and dolphins entered the cave and swam to the music.

    *      Neil Finn performed uncut in this natural auditorium.

    *      The latest live performance was an electronic band called Pitch Black who performed for the Minister of Conservation during 2003 Sea Week. There were 10 boats inside the cave with over 100 people, in the water, and under the water.

    *      Gregorian Chants, Maori haka challenges, opera singers, Swiss yodellers, Irish folk singers, and didgeridoo players too! All have made impromptu performances inside this cave.