New Zealand's longest cave getting bigger

The known length of the country's longest cave continues to grow, 25 years after its discovery within Mt Owen, in Kahurangi National Park.

The Bulmer Cavern is now recorded at 66 kilometres long, more than twice the length of its nearest rival in New Zealand, and members of the latest expedition to the cave are brimming with excitement at what lies ahead, expedition organiser Alice Shanks said.

"We have come away knowing there is still a lot of the cave unexplored. Adding 2km to the official length is big news. We also found that there are a lot of complex tubes in the cave – it continues to surprise us," she said.

The expedition lasted 10 days from December 28, with 20 cavers from Whangarei to Dunedin camping at Bulmer Lake and making the long day trips into the cave to find and explore the new passages.

The cavern was first discovered by Nelson caver John Patterson on New Year's Day 1984 when he dropped a rock down a gaping hole and counted the seconds until it hit the bottom.

He said he suspected at the time that he had found a significant cave, but didn't imagine that exploration would continue unabated for a quarter century.

"I can't believe how big it has become. If you knew what was under the surface up here on Mt Owen you would walk very, very lightly. This ancient mountain is as solid as hokey pokey."

It has taken many cavers, with persistence and commitment, to map the complex maze of tube-like passages, huge chambers, underground rivers and waterfalls, crawl-ways, and dizzily deep shafts up to 120 metres deep, Ms Shanks said.

An electronic surveying instrument was trialled this year, in place of the tape measure, compass and clinometer used to map the cave so far.

This year also marked the 20th New Year expedition to Bulmer Cavern run by members of the New Zealand Speleological Society. These expeditions have become a tradition and have kept the exploration doggedly going through the years when the cave seemed to have come to an end.

Ms Shanks said the quest to explore the cave would continue next summer.

- © Fairfax NZ News