Ogof Hesp Alyn

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Ogof Hesp Alyn
Location: Alyn Gorge
Co-ordinates: 53°10’56"N, 3°12’21"W
Depth: 322 feet
Length: 4,500 feet
Access: contact North Wales Caving Club
Hazards: liable to flooding
Geology: Limestone

Ogof Hesp Alyn is a cave which was discovered by North Wales Caving Club in 1973 in the Alyn Gorge near Cilcain, Flintshire. Its name means Dry Alyn Cave.

Reaching the end of the cave is a serious commitment involving 24 pitches, most requiring specialist Single Rope Technique equipment, and the draining of two sumps. A perpetual siphon is in place at the first sump which does a good job of keeping the water level relatively low, when working properly. Despite its relatively short length, Ogof Hesp Alyn is an interesting cave, well worth a visit for the experienced caver, with much variety and plenty of interesting passage to see.

A BCRA grade 5b survey of the cave exists that was created by North Wales Caving Club in two phases, in periods during the original 70s exploration, and further exploration beyond the sumps in the 80s.

As well as the main passage that meanders through the cave there are several interesting detours including the Northeast Chambers, the Mousetrap series and the Wormway, which gets its name from the numerous worms that live in the sediment.

Much of the cave is wet and muddy, with the entrance series setting the theme for what is to come later on.

With more recent discoveries, the length of cave passage totals 1.2 miles extending over a vertical range of about 300 feet. The entrance would have functioned as a rising prior to the lowering of local water levels by mine drainage. As drainage only took place in the early 20th century, Ogof Hesp Alyn provides a valuable opportunity to study a cave system developed almost entirely by a phreatic processes which remains largely unmodified by vadose streams.

Despite the drainage that now occurs down to the Milwr Tunnel which is several hundred feet below, during periods of intense wet weather the cave can fill completely with water. This is quite rare but any visitor should take care. When the water level recedes, the 'Sand Crawl' can still remain a sump for weeks later.

It lies close to another cave, Ogof Hen Ffynhonnau, which lies about 160 yards further upstream in the Alyn Gorge. These two caves with Ogof Nadolig form the caves part of the Alyn Valley Woods and Alyn Gorge Caves SSSI.

Outside links


  • Appleton, Peter (1974). "Subterranean courses of the River Alyn, including Ogof Hesp Alyn, North Wales". Transactions of the British Cave Research Association 1: 29–42. 
  • Appleton, Peter (1989). "Limestones and Caves of North Wales". in Ford, Trevor D.(ed.). Limestones and Caves of Wales. Cambridge University Press. pp. 233–7. ISBN 0-521-32438-6. 
  • Waltham, A.C., Simms, M.J., Farrant, A.R., Goldie, H.S. (1997). Karst and Caves of Great Britain. Chapman & Hall, 2-6 Boundary Row, London SE1 8HN, UK. pp. 262–4. ISBN 0-412-78860-8.