Vadose – pheratic – what on earth has that got to do with caving?
As I neared the pit the tunnel became narrow and tight as would be expected with water running in a vadose channel. Underground the water is either running above the water table or beneath – resulting in either vadose or pheratic tunnels.
A vadose tunnel such as this one tends to be deep and narrow while a tunnel formed beneath the water table is tubular or elliptical in crossection. With free flowing water – above the water table – most of the wear is at the bottom of the tunnel – both from corrosion and abrasion. The greater the bedload in the river the more the abrasive effect of the running water. Corrosion – chemical erosion is dependant upon many things – the temperature and carbonic acid concentration are the factors that most readily spring to mind.
Another unusual feature of the tunnels that preceed a pit is that they often tend to show increased wear as the lip of the drop is approached – this is the case here as well. Just beyond the water spills over about a 15 foot drop, the tunnel curving under itself and according to those who have descended – gets very wet and muddy.
I looked over the edge and the skinny little rope that someone had looped over a protrusion and opted for a later descent with a rope of my own choosing. I recall my first visit to Dewdney’s Cave (Another Ontario cave) some 15 years ago. I was negotiating “Ongley’s Hole” and using a 1 inch rope that I had not installed. The rope snapped and I fell a short distance landing on my backpack full of photographic equipment.