Geology, Geomorphology and Hydrology
The Ease Gill Cave System extends beneath Casterton, Leck and Ireby Fells around the western and southern flanks of Gregareth Hill. The caves are formed in the Carboniferous (Dinantian) Great Scar Limestone.They contain a wide range of passage types, sediments and speleothems which give an excellent record of karstic evolution and associated surface development through the Pleistocene. The text below is a summary of material provided by English Nature as the system is a SSSI. and of national geological importance. See Conservation Page
Karst Scenery & Cavern Development
The cave systems described all lie within the catchment ofLeck Beck Head resurgence and contain 80 km of known cave passage. They can be divided up into three sectors. The Ease Gill Caverns contains about 60km of passages mainly under Casterton Fell and linked below Ease Gil to Link and Pippikin Pots. The caves of the central part of Leck Fell include Gavel Pot and Lost John’s Cave and have about 12 km of passage with a flooded connection to Pippikin, giving a total length of at least 72 km. The caves of the southern part of Leck Fell form another as yet unconnected system which drains to the Leck Fell caves and is 12 km long.
The Dinantian Great Scar Limestone is about 200 thick with numerous shale bands up to 2 m thick and dips gently to the north-west. The limestone and hence the caves are limited to the west by the Dent Fault. Here the limestone beds are buckled and faulted against Silurian greywackes to the west in a disturbed zone up to 200 m wide. The development of Bull Pot of the Witches is especially controlled by these features. To the south-west the limestone is cleanly faulted against younger beds but this is obscured by thick layers of glacial drift. The limestone outcrop is broken up by many minorfaults and major sets of joints running N-S ad NW-SW. There is also shallow synclines plunging down dip on Casterton and Leck Fells. These have introduced local controls on cave development. The shale beds in the limestone have controlled the level of many of the horizontal passages, while the joints and faults have controlled the location of pitches. Much of the karst surface topography has been obscured bythick layers of glacial till.
The caves systems all derive their surface water from streams which originate on the upper slopes of Gregareth and Crag Hill. These streams all sink close to the Limestone boundary with the Yoredale facies above. The main surface feature is the normally dry Ease Gill Beck. In dry weather the water sinks upstream of Top Sink at the Limestone-shale boundary and the valley is dry all the way to Leck Beck Head. In flood the water flows down the Beck and sinks at a series of sinks from Top Sink onwards. Leck Beck Head lies just east of the Dent Fault and is the resurgence for all the caves between Aygill Caverns to the north and
Ireby Fell Cavern to the south-east. Ease Gill Beck and hence the cave system can respond rapidly to flood with a flood pulse 0.5 m high having been seen making its way down the beck after heavy rain. However the floods also soon subside once the rain ceases.
Ease Gill Caverns is a large cave system containing many types of passage morphology. The caves are accessible through over a dozen entrances mainly located in Ease Gill, except for four which are located on the fells to the north and south. The main feature of the cave system is the abandoned phreatic trunk passage running east-west under Casterton Fell.It starts in Top Sink and heads west to form a complex of old passages in Lancaster Hole. Here it is joined by similar large old passages from Bull Pot of the Witches. it then turns south to end in sediment choked passages heading towards Leck Beck Head.
Almost directly below the high level passages is a fine vadose canyon, Lancaster Hole Main Drain, 2-5 m wide and up to 30 m high. Parts of the Main Drain have cut down from the upper level passages while other sections have bedding plane roofs. There is extensive undercutting along numerous shale bands with collapse in some sections from the passages above. The passage ends under Lancaster Hole in a high rift containing the terminal sump pool. This drains into a large phreatic conduit 30 m below water level and heading straight towards Leck Beck Head.Much of the rest of the system consists of active vadose streamways draining down dip from Ease Gill Beck, including Top Sink, Boundary Pot,Borehole,Pool Sink andCounty Pot. Most of these inlets descend about 50 m to reach the main drain and are complicated by captures and re-routings into pre-existing passages. These passages predate Ease Gill Beck itself as they all have upstream continuations on the opposite south bank eg County Caves Photo: The top of the Cow Dub nick point in dry weather with the middle section of Ease Gill beyond.
Cow Pot is the only major sink on the shale boundary on Casterton Fell. Thestream descends an open shaft and meanders along washed out shale bed to a 45 m pitch from the roof of Fall Pot into Lancaster Hole. The entrance to the latter is close by and consists of a 35 m shaft into the high level passages.To the south side of Ease Gill Beck are other entrances to the system, which consist of another set of high and low level passages interconnected via shafts. Two entrances high on the fell Pippikin Pot and Bye George Pot lead down through constricted immature passages to phreatic trunk routes similar in appearance and level to those in Lancaster Hole. Photo: The normally dry Ease Gill Beck below Cow Dub.
GroupGraham Proudlove at UMIST runs a cave biology email discussion group for cave biology. Contact the website below for more details. http://www.bcra.org.uk/biology/