Caving began to gain a foothold in Canada in the mid-1960s. (Photo: Francois-Xavier de Ruydts)

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With 21 kilometres of surveyed passages, Castleguard is Canada’s longest cave. (Map: Chris Brackley/Canadian Geographic)

Far beneath Alberta’s Castleguard Mountain, cave diver Martin Groves swims farther and farther into a pitch-black unexplored passageway. The beams of four powerful flashlights lashed to his helmet provide the only glimpse of his surroundings. After dropping for 19 metres, the flooded sump levels out, and Groves glides through a gently rising break between layers of limestone, a seam that’s two metres high and about 10 metres wide. Scalloped walls indicate that strong currents once surged here, but today, the water is still and clear. Groves’ fins kick up a fine dusting of sediment. The 39-year-old veteran caver from Wales methodically unspools white line from a reel, connecting it with strips of inner tube to rocks on the bottom of the sump. This line is helping him survey the new passage; it’s also a lifeline leading out.

On his chest, Groves wears a homemade rebreather, an advanced piece of diving gear that scrubs CO2 from exhaled air, then reinjects oxygen so that the gas can be inhaled again. Unlike scuba, or “open circuit,” equipment, where every breath is vented, a rebreather allows divers to remain underwater for an extraordinary length of time. (Groves’ lightweight system can operate for four hours; some bulkier units can last much longer.) Chemical reactions inside the rebreather warm the recycled air and, by extension, the diver — a significant advantage in Castleguard’s frigid waters.

After covering 845 metres in more than an hour underwater, Groves spots “the magical mirror image of air” above. His heart races, and moments later, he surfaces into a muddy, lake-filled chamber. He is through the sump.

The shoreline that Groves crawls onto has never seen human footprints before. His lights reveal a subway-like tunnel, at least three metres in diameter, disappearing into the darkness. Groves, normally a reserved man, a high school math teacher at home, can’t resist the urge to howl. A throaty echo reverberates back, indicating significant open passage.

It’s April 2010, and this isn’t an ordinary cave that Groves is “pushing” (adding distance to). With 21 kilometres of surveyed passages, Castleguard is already Canada’s longest cave. Stretching under the Columbia Icefield in Jasper National Park, Castleguard is internationally renowned for its remote alpine location, its phreatic tubes (perfectly round passages) and its sapphire plugs of intruded glacial ice. Unlike most cave networks, which tend to spider out, Castleguard’s main trail extends in a relatively straight line, more or less parallel to the sump. A journey to its terminus is comparable, in challenge and commitment, to an ascent of El Capitan’s legendary Nose route, in California, says veteran caver Greg Horne, a resource management/public safety specialist with Parks Canada in Jasper. Even in systems such as Kentucky’s Mammoth Cave, which has more than 620 kilometres of explored passages, an exit is never as far.

Groves begins to remove his dive kit, then pauses. Alone, beyond a flooded sump, in a remote cave, he might as well be on another planet. If he gets into trouble here, rescue is all but impossible.

During the 70-minute dive to reach this chamber, Groves’ right hand went numb, the result of a faulty dry glove, and one of his two oxygen meters was giving strange results. (Divers using rebreathers must vigilantly monitor oxygen levels to avoid toxicity.) Taking off his dry suit without help would not only be difficult but also risk damaging a zipper or gasket. A leak in this 4°C water could pose a serious, potentially fatal problem.

On the other hand, wonders Groves, when will he get this opportunity again? This is his third expedition to Castleguard, and getting here required massive support: seven British cavers and 20 members of the Alberta Speleological Society had dragged his heavy diving gear up the Saskatchewan Glacier in sleds, rappelled down the initial eight-metre drop into the cave, then crawled for a few hours through cramped, icy passages to reach the sump. An extensive cave network could continue beyond the sump, speculates Groves, and perhaps prove even longer than the known Castleguard system. The heart of caving lies in the discovery and exploration of new passageways — an addiction that’s luring him onward.

Then “a cold calculating logic took grip,” says Groves. “It’s critical to maintain a very defensive attitude when caving. Contrary to popular belief, this is not a sport for adrenaline junkies.” To safely explore and map the unknown system ahead, he’d need a partner.

Groves takes one last long look at the beckoning void, then pulls on his mask and sinks underwater. The unexplored cave settles into silence. But even as he fins back to his support team, Groves begins planning a return.

Very few opportunities for genuine exploration remain anywhere on the planet, and in Canada, alongside oceans, caves arguably represent the last great frontier. “We have vast areas of potential and very limited manpower,” says Chas Yonge, the operator of Canmore Caverns in Alberta’s Rockies and a seasoned member of Canada’s tight-knit caving community. “In Britain, it’s not uncommon to see a couple thousand cavers descend on a single region each weekend. Until recently, you’d be lucky to find 10 really active cavers in all of Alberta. Bit by bit, that’s starting to change.”

Four months after Groves’ dive added length to Castleguard, Canada’s deepest cave was dethroned by a new contender. The long-standing depth record — 536 metres, held by Arctomys Cave in Mount Robson Provincial Park, B.C. — was shattered by a find in southeastern British Columbia's Flathead wilderness. These were just two breakthroughs in a series of significant discoveries that Yonge and others describe as the “dawn of a new golden age in Canadian caving.”

The journey down what is now Canada’s deepest cave began in 2002, when members of the Alberta Speleological Society spent the summer poking around the limestone deposits south of Fernie, B.C. Most leads yielded nothing. “It was frustrating,” recalls Gavin Elsley, a Welsh caver who had just moved to Canada at the time. “A lot of driving, a lot of hiking, and nothing to show for it.”

As frosts approached and the larch-peppered hillsides of the Flathead River valley turned yellow, cavers explored a recently discovered promising entrance on Mount Doupe, although they managed to penetrate only 100 metres before winter snows clogged the way. Still, they sensed they were onto something big. “The cave just kept huffing and puffing,” says Elsley. “Blowing out air in the morning, then sucking it back in each evening.” On a hot day, so much cold air blasted out the entrance that someone standing 20 metres away would get chilled. The cavers named their discovery Heavy Breather.

All caves breathe, but large drafts indicate one of two things: significant volume (changes in barometric pressure force air in and out) or a second entrance (cold air sinking out the bottom entrance or warm air venting from the top). As soon as the snow melted the next spring, club members began returning to Heavy Breather every weekend to survey and explore. By summer’s end, they had pushed the cave to an impressive depth of 350 metres.

It was the potential for something big that lured one Calgary caver back repeatedly in the winter of 2003-2004. Travelling by snowmobile to the remote region, Jason Morgan was often forced to dig out the entrance (a task that occasionally proved impossible). In 16 solo explorations, he pushed Heavy Breather to a depth of 500 metres — an epic effort that made it Canada’s second deepest cave. But then progress stalled; the cave appeared to have bottomed out.

Meanwhile, a nearby cave — 150 metres higher on the same mountainside — was showing promise. Discovered in 2003 and named Pachidream (because an elephant could fit in its immense entrance), the cave was quickly pushed to a depth of 330 metres. If the caves could somehow be joined and Pachidream’s additional 150 metres tacked on to Heavy Breather (see map on page 46), the new system would be the deepest in North America, outside Mexico.

Surveying new passageways is an integral part of caving’s well-established ethical code. “Scooping booty,” or racing ahead without meticulous note-taking, is frowned upon (see How to map a cave, above). The data collected are so accurate that during multi-year projects, such as the Heavy Breather/ Pachidream survey, each season’s results must be adjusted for changing magnetic declination (the angle between true north and magnetic north), otherwise looping passageways won’t line up. In this case, three-dimensional line plots showed that the two caves were aligned on the same tear fault. (Small tear faults run perpendicular to massive regional thrust faults in the southern Rockies and accommodate localized strain.) The race was on.