Mount Gravatt is primarily composed of quartzite and is generally resistent to weathering and decomposition. But over time it has shed considerable volumes of broken up quartzite debris set in a silty clay matrix down its slopes, particularly its gullies.
The cave has developed in one of those deposits through a process called "piping", whereby water seeping into the ground removes clay particles as it percolates down and outwards. Coarser particles are flushed out through the channels formed.
Small holes have collapsed to the surface in the upper part of the cave and after rain, water enters these to enlarge the cave farther down. It should be noted that the exact mechanism of the formation fo this case is yet to be fully determined.
In order to log this cache, send answers to the following questions to the CO.
To answer the questions there is no need to go over the fence.
1. From GZ (ground zero) what are the sizes of the rocks you can see inside the cave (at the bottom)? Why would you expect this size of rock inside the cave?
2. What type of rocks and sizes of rock can you see around the rim of the cave? Why would you expect these rock sizes to be where they are?