Minya doline on the Nakanai Plateau

Major advances in understanding the Nakanai caves have been achieved through 45 years of expeditions, the first of which was undertaken by Australian cavers, followed by French and British international teams.

The Nakanai Mountains are up to 2,185 metres high and the topography is covered in dense tropical forest. An early report on the caves of New Britain noted that “stories of great river effluxes and cave entrances are common for the area inland from Pomio. An abundance of insects, and multiple species of bats and flying foxes could be found in a single cave in large numbers.”

The first very preliminary exploration to the Nakanai Mountains was undertaken in 1968 by Chris Borough and Kevin Reid of the Port Moresby Speleological Society.

Borough, writing in the Niugini Caver of 1973, told of his experience locating what he called the ‘Big Hole’ in 1968, described the Nakanai karst landscape as consisting of endless sinks with almost vertical sides near the outer edge of each and clothed in dense forest.

Borough wrote:

“It can only be described as impossible country and I never succeeding in pursuing more than a km into it from one edge. Army maps show two remarkable features on one of the limestone plateaux North of Pomio in Eastern New Britain.

“They are a large hole about 1.5 km long and 460 m deep and a smaller hole, 0.5 km wide and 380 m deep. For the average caver, this is too much and I drooled at the prospect of seeing these immense holes.”

French-Swiss cave explorers make their way through the amazing  Nakanai cave system

Borough and his caving colleague, Reid, arrived in Tuke Village by helicopter. To locate the ‘Big Hole’, local people were recruited as guides, but would not accompany Borough and Reid all the way to the sinkhole, as it was regarded as a place of foreboding, where devils and ravenous crocodiles may lie in wait at the bottom.

Upon descending around 60 metres into the hole, the realisation that a full descent to the 300 metres would require specialist equipment saw Borough and Reid return to the village.

The first official caving expedition to the Nakanai Mountains was undertaken by an Australian team in 1972 when Michael Bourke led an expedition (four men and two women) from the University of Queensland Speleological Society to the Ora dolines.

During the 1972-73 expedition, the team explored the northern doline, following a river at the bottom to a cave chamber 15-27 metres wide and about 27 metres high. They charted 168 metres of passage before progress was halted by a waterfall that occupied the entire cave floor.

The Australian team noted that it should be possible to explore further by traversing above the waterfall. Moving upstream from the bottom of the doline they entered a large cave chamber 600 metres long and 67 metres deep, with huge stalagmites hanging from the roof.

By moving through the chamber in a southerly direction they emerged out in the bottom of the twin doline. Walls as high as 100 metres rose up from the bottom. Re-entering the cave from the southern doline, the cavers followed an old stream passage back to the river.

Downstream was a spectacular waterfall, and upstream they moved through a beautiful section along the river to a lake. Bourke wrote: “Calcite curtains, candle wax stalagmites, flowstone and stalactites, lavishly decorate this area.”

Following the Australian expedition, a French caving expedition continued the research in 1978. Numerous expeditions came later. The 1979 Swiss expedition to Kavakuna Cave and descended to 320 metres.

It resulted in tragedy when one of the cavers drowned in a caving mishap, and the rescue helicopter, en-route to Rabaul, had engine failure and crashed into a river.

In 1980, a French-international team led by Jean Paul Sounier, explored the three entrances of Kavakuna Cave and undertook the initial exploration of the Nare river cave near the village of Nutuve.

In 1984 and 1985 the British caving team completed the exploration of Nare Cave, the Pavie River Cave and the Gamvo Cave system. Towards the end of the expedition a reconnaissance trip looked at the Ora dolines. The British team felt that the cave warranted a further visit, but it was to be over 20 years before they returned.

The 1985 expedition to Nakanai, undertaken by the French international team explored Minye Cave, and Muruk Cave. A decade later during the 1995 expedition, the French team dived the final sump (a passage in a cave that is submerged under water) and enabled Muruk to become the first 1,000- metre-deep cave documented in the Southern Hemisphere.

In 1998, during a helicopter reconnaissance flight over the area between Galowe Gorge to the east, and the huge Wunung Gorge to the west, French caving expedition leader Jean-Paul Sounier was surprised to see that, unlike Galowe Gorge, no rivers poured into this 1,000-meter-deep Wunung Gorge canyon.

This begged the question: where was the water flowing into the mouth of the coastal Wunung River coming from?

The mysterious ghost rivers of the Wunung Gorge became the subject of an expedition in 2016 and 2018. The British cavers returned in 2006 with a team of 12 from the UK, France, and the United States.

The UK expedition, led by David Gill, involved a two-month expedition to complete the Untamed Rivers Expedition, first commenced in 1984. The primary purpose was to complete the exploration and mapping of the Ora river cave and to search for other caves in the area.

The secondary objective was to gather data with the aim of establishing a Nakanai Conservation Area which would be proposed for World Heritage status to protect the cave area from destruction by logging.

During the British expedition, over 12 kilometres of river caves were explored and mapped. The Phantom Pot cave was mapped during the early stages of the expedition at an altitude of 1,045 metres. Phantom Pot was surveyed for 3.9 kilometres, over a depth of 191 metres.

In January 2016, an international team led by French caver Jean-Paul Sounier explored a gigantic black sinkhole spotted in aerial images. On a plateau along the left bank of Wunung Gorge, a black and white mark indicated a surface sinkhole with a black hole almost 100 meters wide and 100-150 metres deep.

During the ‘Black Hole’ Expedition in 2016, the team, spent four weeks surveying and mapping caves and galleries. One cave was named Wild Dog Cave after a long howl, similar to that of a wolf pierced the previous night.

In the sinkhole they initially named Dooble, the ceiling is magnificently decorated with white stalactites and streams, waterfalls, and underground lakes flow through the galleries. The discovery of the 714-metre-deep cave named as Dooble was re-named the Christian Rigaldie Cave to honour a caver who was part of the first French expedition to the Nakanai Mountains in 1980.

A cave mouth in the Nakanai Mountains

Although he never returned to Nakanai, Rigaldie contributed to the funding of several expeditions and died of illness in 2015.

At 714 metres deep the Christian Rigaldie cave now ranks as the second deepest cave in Papua New Guinea, after the Casoar (Muruk) cave network.

In 2018, the French-led team returned to explore the underground drainage system of the Christian Rigaldie Cave network, which flows deep beneath the Wunung Gorge.

The ‘Ghost Rivers’ expedition documented 16 cave chambers beneath the Nakanai Mountains.

After three weeks exploring blocked cave entrances, the team found a collection basin with fast-flowing underground rivers, exploring and charting six kilometres of networks with two major cavities more than 500 metres deep.

The biggest of these cavities, at around 580 metres deep, was named Phillipe Pato Cave (to pay homage to a former porter), the third deepest cave in Papua New Guinea.