The launch of the 5th edition of Mendip Underground caused somewhat of a surge of interest in certain caves in which it contained updated descriptions, photos and rigging diagrams, Mangle Hole near Sandford being one of them. It was the rigging topo which caught my attention as it suggests some nice free hanging pitches with multiple rebelays and a sump at the bottom, what more could you ask for !
http://www.mcra.org.uk/registry/sitedetails.php?id=851
The reality is somewhat different, its reputation does seem to precede it and it is seldom visited but I quite enjoy a trip there and have undertaken a few club trips, several digging trips, several surveying trips plus a failed dive trip.
As there was no decent published survey of the cave (and there still isn’t) I decided with my new found cave survey skills I would have a go myself. I was joined by Pete Hall and we set about surveying the cave, I don’t remember much detail of the trip itself but I can remember feeling quite frustrated when sitting down at my computer with the data afterwards knowing what shape the passages and chambers actually were and seeing the shapes that I was to draw on the survey to represent them.
The problems lies in that the cave is very steep in nature, the entrance rift is very narrow floor to ceiling but wide in the wall to wall dimension, the chambers are large and vertical in nature with lots of alcoves and side rifts, the route to Aldermaston Chamber is small, complex and muddy. When the splay shots are viewed in plan view the whole cave looks very different to the reality.
At the time I was trying to learn how to draft surveys in Therion but perhaps this multilevel cave was a bit to challenging for my basic skills. Instead I found a handy export function of PocketTopo where the raw data is exported as a 3d *.dxf file, this can then be loaded in CloudCompare where it approximates the walls based on splay shots and shows a 3d model which can be spun around and viewed and understood more readily then a plan and elevation view.
