Delving Into Tasmania's Underground

Cavers discover a flooded subterranean passage that sets a new record for Australia’s deepest cave system.

- Stephen Fordyce

FOR MORE THAN AN hour I’d been pushing through the silty, submerged tunnel, using the rock walls to guide me. The water was cold and in places the passageway was uncomfortably tight. I was searching for a way through a flooded passage deep within Niggly Cave, on the Junee River near Mount Field National Park, north-west of Hobart, Tasmania. I’d left the expedition team I was part of at the edge of a pool at the cave’s end: known as a terminal sump, it’s the furthest point cavers can access before the tunnel becomes submerged.

I was diving alone and looking for an orange string guideline I’d used to mark my route through a different cave, the nearby Growling Swallet, four years earlier. Back then, I’d dived some 500m along a narrow tunnel before reaching the predicted limits of my breathing gas supply.

I’d severed my guideline there and secured its end to some rocks before heading back. Now I was trying to find that point from what I hoped was the other side. If I could reach that old guideline and prove the two caves were connected, our team could show that this cave system is the deepest known in Australia.

The height of a mountain is measured from sea level to the summit but the depth of a cave system is determined by calculating the height difference between its highest and lowest points. So, if you’re chasing a cave depth record – trying to find the deepest cave – it makes sense to explore upwards, looking for high points, and downwards, looking for low points, but it also makes sense to search sideways.

If you can find a link between two nearby caves, proving they are joined, then you can combine the highest known point of one and the lowest of the other to chart a new depth for the system. And that was exactly what I was trying to do.