An impressive entrance shaft drops down into a small streamway that soon reaches a sump that eventually feeds the Cwm Dwr streamway after first passing through Cwm Dwr II.
SN 85876 15961
The draughting shakehole was found by Brian (Jopo) Jopling in 1979 and dug to reach the streamway at Easter that year with the help of Bristol Exploration Club members.
The cave is located in the dry valley behind the main Penwyllt quarry. The entrance is marked by a large spoil pile.
Swansea Valley Google map showing the location of Twll Gwynt Oer and other caves in the area.
The entrance shaft has timbers placed across to safeguard livestock, please replace after any visit.
At the bottom of the shakehole a three metre deep hole lined with pipe drops onto a capped 8m shaft. A large concrete lintel and a bolt allows the rigging of the shaft which drops down to a spoil pile where the streamway can be heard. The small streamway flows through a tight bedding near the bottom of the shaft and can be reached in two directions. Upstream (north) reaches a boulder collapse after approx 30 m with the stream entering from a too tight bedding. The passage splits and rejoins in the area of the boulder collapse where there are small areas of calcite formations evident. Downstream, the passage enters a constricted sump after a similar distance. The sump was originally tight requiring digging, until at 3.6 m the passage enlarged to a comfortable body size tube. This ascended to a blind airbell, 2 m above the main continuation. After 7.6 m the continuation underwater became too tight at 2.4 m depth, 14 m from base. The sump has now largely been removed by digging, now being low and choked with rocks. A small tube choked with rock can be seen just above the start of the current sump. The water flowing in this small cave later reappears from the upstream sump in Cwm Dwr II, flows through that cave and then enters Cwm Dwr Jama via the upstream choke.
8m ladder | belay to in-situ hanger and concrete lintel
Cambrian Cave Registry for Twll Gwynt Oer
Welsh Sump Index
| Cave Diving Group | Duncan Price
South Wales C.C. Newsletter
| No.93 p3-4 (1981)
Cave Diving Group Newsletter
| No.52 p29 (1979)
Nothing of note.
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