Jun 272011


Hanging root mats in Olwolgin Cave

About the dive

Olwolgin Cave is located on the Roe Plain, Western Australia, not far from Burnabbie Cave. As I posted previously, the Roe Plains caves are quite different from the white walled, blue water, big tunnels of the better known Nullarbor Plain caves. The first thing you notice is the yellowish tint to the water (but not to the walls) and the narrow, twisting, multilevel nature of the cave.

With the water level close to the surface, tree roots from the desert above intrude into areas of the cave. However, the Roe Plains cave also have unique salinity characteristics. Instead of a single halocline with a distinct mixing zone between layers of fresh and salty water, like might be seen in the Mexican caves, the water gets progressively saltier (and denser) as you descend. This means there is a mostly fresh layer of water present only at the very top levels. In areas with air pockets between the roof and the water, tree roots grow down cracks in the ground and then spread out over the surface to take advantage of this fresh water.

Warning signage in Olwolgin CaveAs the roots grow and spread out, they also get heavier. Eventually, a network of roots for a particular tree will drop down into the high salinity water below, killing those roots, and forcing the tree above to start again. These curtains of fibrous tree roots hang like ghostly veils in the cave, swaying gently in the flow created by divers moving past. Because they are no longer alive, the hanging roots are extremely fragile, and we took utmost care when approaching them.

As you can see in this second photo, Paul has established floating signs in the cave to warn divers visiting the passage, and to thank them for their care once the delicate area has been passed. By following the guideline around the edge of this room, exhaust bubbles ascend safely into the rocky roof rather than destroying these unique formations. This trail marking is a dry caving technique, successfully adapted for underwater with laminated signs and some floating polystyrene. On the floor underneath there’s a decomposing pile of root mat that has come disconnected from the tree above, and is likely contributing to the unique colours and composition of the cave water and air pocket above.

About the photo

This particular photo of the roots is not particularly well composed or thought out – it was an opportunistic shot as we travelled through. The previous day I had modelled for Harry to take shots of the huge roots in the area of the cave known as the Hanging Gardens of Babylon. There were a few real heart in the mouth moments as either my fins or my bubbles got too close for comfort and the whole formation started to sway…luckily, control was maintained and no damage was done. These shots can be seen in the Desert Diving article published in the July/July edition of Sport Diver.

While this may not be the best specimen or the best shot of these spectacularly fragile formations, it is a picture with a backstory. These particular roots are in the main passageway of the cave, with the guideline splitting around the room to guide divers along the side. The first person to swim directly through will destroy this scene. Knowing this, I wanted to capture a little piece of history, and one I hope will be there for others to experience for some time to come.

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