, Northern Outcrop - Central (Penwyllt to Penderyn)
map using leaflet map:
This is one of the 3 entrances to Ogof Ffynnon Ddu.
The cave is a Nature Reserve and Access is controlled by the OFD Management Committee and administered by SWCC A permit for entry should be applied for from the SWCC permit Secretary. Parties wishing to enter OFD 1 must have a leader who is recognised as a leader for the system.
Current Access arrangements
OFD 1 Entrance is not the original entrance to OFD, but a slightly newer one dug to bring the entrance on what was Cyril Powell's land.
OFD is the deepest (from an aven in OFD 3 to FD) cave in Britain and the third longest, and ranks amongst the longest caves in the world. The cave comprises of a complex system of large and small fossil passages, finely decorated in places and a fine and very long streamway. It is divided into four distinct sections :
OFD 1, Cwm Dwr, OFD 2 and OFD 3
The length of OFD 1 is around 6000 metres. A complex series of passages in the entrance lead to an active passage from which at various points further passages can be reached. The stream is liable to flood. Divers proved the connection to OFD 2 in 1966 and to Cwm Dwr in 1967 and Top Entrance was dug open in 1967.
CSS nl 42 (8/9), p.92, 2000, Stuart France, OFD Resurgence Depth and Temperature Variation
CSS nl 42 (8/9), p.102, 2000, Stuart France, How fast does OFD flood? [can be within 2 to 4 hours of rain]
Cave and Karst Science 27 (3), pp.101-108, 2000, Clark R.L.Friend , Contribution of airflow to the control of seasonal variations in radon concentration in Ogof Ffynnon Ddu, Penwyllt, South Wales
CSS nl 43 (5), p., 2001, Stuart France, Comparative flooding rates for DYO and OFD [OFD rises earlier and drops faster]
CSS nl 43 (6), p.64, 2001, Stuart France, Comparative flooding rates for DYO and OFD (graph corrected) [OFD rises earlier and drops faster]
Cave and Karst Science 31 (2), pp.63-76, 2004, G.T.(Jeff) Jefferson, Phil Chapman. Julian Carter and Graham Proudlove, The invertebrate fauna of the Ogof Ffynnon Ddu cave system, Powys. South Wales, UK