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March 2016 Issue
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The longest cave

Cavers at one of the two permanent camps in Bulmer Cavern. Photo: Neil Silverwood

Neil Silverwood reports from the 31st annual expedition to explore the extensive cave network known as Bulmer Cavern beneath Mt Owen

The Hughes 500 climbs steeply above the bluffs of Bulmer Creek. Below, 20 cavers tramp up an improbably steep route, wading through the creek, wasp-infested bush and overhanging cliffs on course to the small lake at the head of Bulmer Creek. I’m glad to have drawn the long straw to fly in with the expedition gear. It’s a surreal feeling to be dropped off at the lake, feeling fresh and with dry feet.

The expedition base camp is located beside the lake, beneath Castle Rocks on the southern side of Mt Owen. The lake is shallow and teeming with an unusually high diversity of life. Massive marble cliffs tower overhead, topped by an undulating sea of karst. The bizarre landscape is riddled with holes and cracks etched out over hundreds of thousands of years by rainwater and snow melt making their way underground.

A few hours later, the rest of the team begin to trickle in. I feel guilty watching Lindsay Main, a wiry caver nearly 20 years my senior and one of the expedition organisers, arrive and make his way towards the camp kitchen. Lindsay sits down heavily at the sheltered rock bivvy. “It’s good to be back home again,” he says, a thought likely echoed by many of the team who, like Lindsay, have attended the annual expedition numerous times. Indeed, Lindsay and his partner Alice are the last of the original expedition members who still come to Bulmer each year. Once a passionate and accomplished mountaineer, Lindsay was drawn to caving in the 1980s by the opportunity to explore new ground. “Most of the accessible, obvious alpine routes had been climbed by then,” he says. “But caving was still in its infancy. You could walk straight into unexplored caves then – and you still can today.”

Bulmer Cavern was found in 1985 by the first group of cavers to visit the south Owen karst field just north of Murchison on the South Island. That expedition was led by Oz Patterson. Before this, cavers appear to have been put off by a bleak geological report that indicated there was little potential for significant discoveries on the south side of Mt Owen. The geologist who wrote the report believed glacial erosion and infill would have filled in all of the potholes and potential cave entrances.

It was a prediction that couldn’t have been more wrong. On the very first day searching the tops above Bulmer Lake, Patterson made an amazing discovery: an enormous entrance leading to large, ancient tubes heading deep into the mountain. Tellingly, a strong cold breeze was blowing out of them. The upper level passages were high and dry, long since abandoned by the water that had created them. News of the discovery spread like wildfire and in no time Patterson had a capable group of volunteers fired up and ready to help explore.

Lindsay was one of the first to sign up. “At first our goal was to push the system downward,” he says. “What we didn’t realise was that the true potential wasn’t in its depth, but in its length.”

In time, Bulmer Cavern became New Zealand’s longest-known cave system – it currently extends to 72km – with the potential to push it even further as new passages are discovered.

Cavers follow traverse lines across the intimidating 'Who Dares Wins' climb near the end of Bulmer. Photo: Neil Silverwood

Cavers follow traverse lines across the intimidating ‘Who Dares Wins’ climb near the end of Bulmer. Photo: Neil Silverwood

The exploration of Bulmer ebbs and flows. “We often run out of obvious leads but up here you just need one breakthrough to open up a mass of cave,” says Lindsay. One such breakthrough came at the bottom of a network of shafts and rifts called the ‘Lion’s Den’. In 1987, Bulmer was 7km long and cavers seemed to have reached its end. One of the last major leads was a large circular shaft big enough to hold two milk tankers standing end on end. After descending some 200m and forcing a route through a tight rift, cavers broke out into the master system below. They had discovered the lower levels, a vast tangle of interwoven passages stretched out beneath the mountain like the tentacles of an octopus. This discovery put Bulmer Cavern firmly on the cavers’ map. Exciting new interlinking passages were explored in the centre of the system and the cave became the 32nd longest in the world. But the far reaches of Bulmer remained static. After a wave of exploration, it seemed that once again cavers had reached an impasse.

Then in 2011, I joined a small team that made its way to the furthest reaches of Bulmer Cavern to attempt to trace the path of a stream and find where on the surface it emerged. We used a highly concentrated, but safe, green dye called fluorescein. It can be detected at 1-2 parts per million. Just a pinch of the dye powder is enough to turn an olympic swimming pool neon green.

The results defied logic. Charcoal bags placed in Bulmer Creek that would indicate passage of the dye came back negative. Instead, the dye appeared on the opposite side of Mt Owen, flowing north for 8.6km, in the opposite direction to the southerly flowing cave streams, into Blue Creek. It was something nobody could have predicted.

The dye trace altered what we thought we knew about Bulmer Cavern. Caves very rarely cross drainage divides, most are linear and we always believed all streams in Bulmer flowed south. Some in the caving community questioned the results of the dye trace experiment; it just seemed too hard to believe. I still struggle to comprehend that water in Bulmer flows both south and north, resurfacing on opposite sides of the mountain. There are still a lot of unanswered questions regarding the hydrology of the system, but we now know the entire mountain must have connecting underground passages throughout. As Marcus Thomas, one of the leading explorers in Bulmer, put it, “the whole thing would make a terrific thesis.”

The future for Bulmer Cavern is promising. “There could conceivably be a massive unexplored system between Bulmer Cavern on the south side of Mt Owen and Blue Creek to the north,” says Thomas. I asked him if he thought we’d see a connection between Blue Creek and Bulmer Cavern in the foreseeable future. He paused, then said: “No, I don’t think so, not in our lifetime.”

The dye placed in the furthest reaches of Bulmer reappeared at the Blue Creek Resurgence, 8.6km to the north. Photo: Neil Silverwood

The dye placed in the furthest reaches of Bulmer reappeared at the Blue Creek Resurgence, 8.6km to the north. Photo: Neil Silverwood

During the recent 31st Bulmer Cavern expedition in January, a team of four cavers, including Thomas and I, headed to ‘Camp 3’, the furthest underground point from the entrance, and the ‘Far and Away’ stream. It was my 30th week-long underground camping trip in Bulmer and I felt like I could almost do the route in the dark; each climb, pitch and awkward squeeze is etched into my memory. It takes the best part of two days to get to Camp 3, a large chamber roughly the same temperature as a refrigerator. The environment, temperature and humidity are constant. Sleeping bags are left permanently at the camp so there is less to carry in, but no-one had come this way for seven years and we found the bags wet through and mouldy.

Beyond Camp 3 lies some of the bleakest alpine caving imaginable. A stream, likely fed from snowmelt, cuts its way deep into the shattered marble. Exploration and progress here has been difficult as there are a number of waterfalls. On past trips we aid-climbed our way up loose, mud-covered walls searching for horizontal passages only to discover yet more waterfalls.

After a cold night in damp sleeping bags, we headed to the end of the cave, two more hours beyond camp. It was as bleak and desperate as I remembered. Thomas and I pushed up a tight, meandering rift while the rest of the team returned to camp. Eventually, we pushed through a squeeze between boulders and the cave opened up. It was the furthest anyone had ever been in Bulmer. We looked around the large room we’d discovered but couldn’t push on; the way blocked by a narrow 10m waterfall too difficult to climb.

Perhaps the greatest moment of any underground camping trip is returning to the surface. Tired eyes, used to the light from dim LED torches, struggle to cope with the brilliant sunshine. Colours seem overwhelmingly bright and there’s a strange desire to hug trees and any people you come across. Camping underground really makes you appreciate all these things. Appreciate life.

Sitting in my warm, dry house at the end of the trip, I find myself thinking about Bulmer, trying to work out where the way on will be. One way could be to find a new entrance to the north of Mt Owen (at time of print another expedition to do just that was underway). On Culliford Hill and in the Hay Paddocks near Sentinel Hill there are literally thousands of shafts, many unexplored.

“It’s like looking for a needle in a haystack,” one of the team members on the northern expedition told me before. “We’ll be lucky to find the right hole, but if you don’t try, you certainly won’t find it.”

Cavers have to be optimistic. For every hole and narrow passage prospected, 99 out of 100 are dead ends. Perhaps a way will be found into the system below north Owen, helping piece together the puzzle. Or perhaps it won’t. But one thing is certain; as long as there is unexplored cave on Mt Owen, cavers will keep returning until Blue Creek and the Bulmer Cavern system are connected and the chapter can be closed.

 Mapping a cave

Cavers map out every inch of cave explored. They use a compass, inclinometer and tape measure to record direction, elevation and distance. An experienced team can survey at high speeds and with good conditions can record more than 1km a day. “It’s one of the most exciting aspects of the sport,” says caver Marcus Thomas. “It’s fascinating to watch the cave grow outward on a map, inch by inch.”

Technology also helps, with many cavers now using a device called DistoX, which uses a laser to measures distance, direction and inclination.

Map of Bulmer Cavern. Credit: Marcus Thomas

Map of Bulmer Cavern. Credit: Marcus Thomas

Get into caving

If you would like to experience caving there is a number of clubs around New Zealand. The New Zealand Speleological Society (NZSS) is the umbrella organisation and the first point of call if you are interested in the sport. For more info, visit