Priddy Caves

Site of Special Scientific Interest · 51.2543, -2.6771

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Also within

Somerset County Mendip Hills Scenic Area

Condition (Natural England)

Favourable (5)
UnitFeatureConditionArea (ha)Assessed
ST528507 — Favourable 76.06 2010-12-02
ST528511 — Favourable 76.06 2010-12-02
ST539506 — Favourable 76.06 2010-12-02
ST543500 — Favourable 76.06 2010-12-02
ST549500 — Favourable 76.06 2010-12-02

Habitats

Fast flowing river and stream

Geology & landscape

Geological Feature: Cave / Cavern

Landscape processes: Karst

Description

Area, 67.6 ha. 167.0 ac. Description The Priddy Caves System contains about 16km of surveyed cave passages divided between a number of major and minor networks. The three largest networks, Swildon's Hole, St Cuthbert's Swallet and Eastwater Cavern exceed 100 metres in depth; in all the caves the detailed disposition and form of the passages can be seen clearly to have followed marked lines of natural weakness in the rocks. The two most extensive systems are those of St Cuthbert's Swallet and Swildon's Hole, both of which were formed by the erosive action of water flowing beneath the water table at considerable pressure so called phreatic development. Swildon's Hole is a world famous example of a shallow depth phreatic cave, which shows a very well developed dendritic pattern of drainage and contains extensive clastic and stalagmite fills. St Cuthbert's Swallet is a classic example of a deep phreatic cave system, containing inclined bedding plane mazes at many levels, fault guided rifts and some magnificent chambers; in successive phases of sediment deposition, stalagmite deposition and stream erosion have been recognised. Eastwater Cavern is a steep labyrinthine swallet cave, which was the first of its kind to be opened in Britain, by Herbert Balch in 1902; the cave exhibits classic relationships between wide, low inclined bedding planes 'traverses' and deep narrow 'canyons' and also, contains Mendips' largest penetrable boulder ruckle. Hunter's Hole is an excellent example of a shaft complex draining a closed depression. The roof of the main shaft shows a variety of features such as soil and boulder bridges and scalloped and speleothem lined rifts, all draining the surface depression. This cave differs from the others at Priddy in apparently not having formed as a stream swallet. Cave sediments found within the systems, together with the information which can be deduced from the physical form of the caves, provide geologists with the means to obtain a better understanding of the geological evolution of southern Britain during the Ice Ages.

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea