Minyé sinkhole and cave

The incredible Nakanaï Mountains

The exotic island of New Britain has many natural wonders – volcanoes, geysers, and numerous endemic animals, and plants. But unsurpassed wonders hide in Nakanaï Mountains – up to 2,185 m high mountains in the central-eastern part of the island. The total area of these mountains is 5,500 km².

Heavy rain

This place has an equatorial climate and the upper reaches of mountains belong to the wettest places in the world with yearly rainfall over 6,000 mm and reaching 11,900 mm.

This very frequent heavy rain and equatorial climate cause several interesting effects. One is easily visible – Nakanai Mountains are covered with dense, wild rainforests, considered to be one of the most biodiverse ecosystems in the world, with a large number of endemic species of plants and animals. Even nearly vertical cliff faces here are covered with dense jungle.

Karst

Another effect is even more interesting: Nakanai Mountains are made up of very thick (up to 1.5 km) layers of Miocene limestone, covered with a fragmentary layer of fine volcanic sediments from Pliocene. Perfect conditions for the development of karst processes!

Heavy rain creates rivers and rivers in the mountains over time create deep valleys. Throughout the last 200,000 years in the Nakanai Mountains have formed eight giant canyons with a depth reaching 600 – 1,000 m. The upper reaches of these canyons and their side ravines contain some of the most powerful springs in the world. So – these by far are not common rivers: the upper parts of these rivers are located deep inside the limestone layer, in giant caves. It is possible that these are the most powerful underground rivers in the world.

In some places in these caves formed enormous voids, which after some time collapsed (and many more for sure are going to collapse in the future). Now, these collapsed voids look like giant holes with underground rivers deep below crossing their bottoms – they can be compared to keyholes with a small fragment of the underworld visible through them.

In Nakanai mountains have been found numerous such sinkholes (also called collapse dolines and – if they are REALLY large and with vertical walls – tiankengs) – some have just opened and represent a narrow opening above giant underground voids. Others represent giant wells with vertical walls and others have degraded – they just resemble enormous, jungle-covered depressions.

Sinkholes of Nakanai Mountains belong to the most impressive, "best" sinkholes of the world. It is a bit hard to select – but it is possible that the most impressive among them is the Minyé sinkhole, although there are comparable ones, like Naré sinkhole.

Sinkhole

Minyé sinkhole looks like a giant hole in the green jungle, visible even in comparatively blurry satellite images. This hole is nearly perfectly round, with a 350 m diameter. The depth of the sinkhole is 400 – 510 m – the Eiffel tower here would be far below! The measured height has that much difference because the sinkhole is located on the slope – the upper rim is approximately 100 m higher than the lower rim.

Area of sinkhole is approximately 75,000 m², volume – 26 million m³. Equatorial climate helps to sustain jungle cover everywhere – on the bottom and even on the nearly vertical walls.

Floor of the sinkhole is crossed by a powerful river – from the upper rim it may look like a narrow stream, but it isn’t. The volume of the stream is 15 – 25 m³ per second. Doesn’t tell much? This would be enough to supply the needs of some 14 – 16 million Europeans. After torrential rain, the flow may increase significantly.

Cave

Initially it was considered that the cave passages at the bottom of Minyé are not too significant. This was not true.

Thus far there have been investigated 5,421 m long passages, but this may be just a small part of the system.

Powerful subterranean rivers require large passages – and caves under Minyé certainly are giants in this respect. The largest room in this cave is Tuké chamber – one of the largest cave chambers in the world. It is 240 m long, 200 m wide, and 180 m high. The floor area of this chamber is 48,000 m², volume is 6,240,000 m³.

Cave system contains exciting cave organisms, many of them endemic.

Exploration

Minyé was known to locals long ago.

Minyé, just like some other geological miracles of the Nakanai Mountains, were first researched by Australian speleologists in 1968 who descended to 60 m depth. Then French speleologists researched it in 1978 (first descent to bottom) and 1984 (French/ Swiss expedition), numerous expeditions came later as well.

Caves in Nakanai Mountains belong to the most exciting caves in the world but they require a lot – high skills in cave alpinism and cave diving, flawless health, and last but not least – a fat purse.

Caves in Nakanai belong to the technically most difficult caves in the world. Everything here is challenging – coming to this far-away (when looking from Europe or the United States) place, ascending the wild, jungle-covered mountains along the slot canyons of torrential rivers in nearly constant rain. Imagine building your camp in the wet jungle, in constant rain. Jeez, think about the bad odor from feet, better have separate tents… Then one should descend half a kilometer deep, through the jungle – can you imagine hanging in half a kilometer-long rope?

And only then it begins… Pristine, incredibly beautiful and opulent dripstone formations, giant passages, and the constant roar of rivers struggling through the cave and falling over countless waterfalls. Only the most experienced explorers should dare to dive into this powerful stream to pass the numerous siphons.

References

1. Waltham T. Tiankengs of the world, outside China, Speleogenesis.info. Accessed 24.07.10.
2. Vuvu 2010, speleological expedition. Accessed 24.07.10.

Minyé sinkhole is included in the following list: