It’s a new year, and over two months since my Great Barrier Reef trip. I figure I should pull my finger out and finish this story... I started writing this post with the intention of summarising the rest of the trip, but got stuck on this one, special dive…
GREAT BARRIER REEF 2012 – PART 5 – NORTH HORN WALL
North Horn Wall – Deep Dive
One of the (many) cool things about diving from Spoilsport, is their willingness to treat divers as adults. If divers can show training, qualifications and experience, they may dive within these. When asked if I’d be interested in doing a deep dive on the wall at North Horn, I jumped at the chance.
From 30,000 to 80,000 years ago, the sea level was 60 to 80 metres lower than it is now. Around 30,000 years ago, an ice age dropped the sea level to at least 120 metres lower than today, and from 20,000 years ago the sea level rose again.
(More on sealevel and ice ages: http://www.cmar.csiro.au/sealevel/sl_hist_intro.html)
On the wall at North Horn, there is an undercut, created by the old sea level. It starts at about 65 metres below today’s sea level. This was a great reason to go deep.
First thing was to look at available gas. One of the regular crew was absent from this trip, so I was able to borrow a set of twin 7 litre tanks – filled with air – backgas sorted. Now 18 litres isn’t heaps, so I slung a 10L ali of air and another of EAN60. That was more like it.
Mmmm, twin 18L tanks - anyone know a good chiropractor?!
Diving on air, I wasn’t keen to push narcosis too hard so decided 50 metres was a sensible depth. With the vis being so good, this would let me see the top of the undercut and experience a taste of deep, coral-wall diving.
I use V-Planner for my dive planning and run the VPM-B model set to Level 3 conservancy. This means I start my deco stops a little deeper than traditional models and spend a little more time decompressing than an aggressive model.
Planning a technical dive is something I enjoy. I derive a great sense of satisfaction when I complete a dive that I planned and this was no exception.
We rolled out of the tender and started our descent. As we followed the coral down to 50 metres, the wall just kept going. But just below us was an obvious change in the slope of the wall. This was the old sea level and it was worth the dive just to see it. From there, the wall sloped away into the abyss.
Soft corals festooned the wall, which soared above us, almost to the surface. The visibility was incredible. Was it 90 metres, 100? Who knows? It seemed infinite. Some of the wall had shallow gullies coated in sand. Looking like snow-coated slopes high on a mountain, this was debris from above, part of the continuing cycle of deposition and consumption.
I kept a weather eye on the blue, hoping to see something big. Looking up I spotted the unmistakeable outline of a great hammerhead shark. Unbelievable. It was circling about 30 metres above us. Another highlight.
Yet another advantage of wall diving is the ascent. Forget blue water deco stops, swimming up a wall means there’s always something to see. The perfect way to end a dive, swimming with reef fish among the coral at the top of the wall.
Back on Spoilsport and smiles all around. What a dive!
With thanks to Trevor Jackson (Spoilsport boat driver and my buddy for the dive), Craig Stephen (Operations Manger, Mike Ball Dive Expeditions) and Damian Siviero (Photographer Extraordinaire and fill-meister).