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This work is protected by copyright and other intellectual property rights and duplication or sale of all or part is not permitted, except that material may be duplicated by you for research, private study, criticism/review or educational purposes. Electronic or print copies are for your own personal, non- commercial use and shall not be passed to any other individual. No quotation may be published without proper acknowledgement. For any other use, or to quote extensively from the work, permission must be obtained from the copyright holder/s. 7 THE PALAEOHYDROLOGY OF THE MORECAMBE BAY KARST 116 7.1 Introduction In common with many other karst areas, the Morecambe Bay area has been the focus of a considerable amount of palaeohydrological research. This work has tended to con­ centrate on two particular aspects of cave development: firstly, the problem of the "phreatic network" caves, variously regarded as Tertiary relicts or products of polje-margin processes; and secondly, the question of the development of the regional drainage system. The present study attempts to resolve the question of "phreatic network" cave formation (see 7.2) and applies the methods detailed in Chapter 6 to specific cave'systems in an effort to understand the role of these caves in the overall development of the drainage system (see 7.3 and 7.4). Finally, an attempt is made to synthesise these findings into a model of the palaeohydrological development of the whole region (see 7.5). 7.2 The "phreatic network" caves 7.2.1 Introduction Certain of the caves within the Morecambe Bay area have been regarded as unique in terms of their method of formation. These caves, termed by Ashmead (1969a, 207; 1974a, 213) "phreatic network" caves, have been considered for some time as the only true "water table" caves in the British Isles (Waltham, 1974, 89-91); that is, caves which have been formed by solutional action at the water table and which tend to be nearly horizontal despite the inclination 117 of the rock. They have also been seen as evidence for phases of karstification in Northern England dating back as far as the Tertiary (Sweeting, 1970, 239). To date, five groups of caves have been placed in the "phreatic network" category (Fig. 7.1): (i) Roudsea Wood: northern system (SD332826) (Fig. 7.2), southern system (SD333825) (Fig. 7.3). (ii) Nichols Moss: Shale Cave (SD434827) (Fig. 7,4) Fairy Cave (SD434827) (Fig. 7.4) Yew Tree Cave (SD434826) (Fig. 7.4) Fissure Cave (SD434826) (iii) Gilpin Bank Caves (SD4687) (iv) Levens Cave (SD484857) (v) Hale Moss: Brackenthwaite Cave (SD498772) (Fig. 7.5) Hazel Grove Cave (SD499771) (Fig. 7.6) Hale Moss Cave (SD502777) (Fig. 7.7) 7.2.2 Previous Work Two contrasting hypotheses have been advanced to explain the existence of the "phreatic network" caves, each having wide implications for the chronology of karst develop­ ment both in the area and in northern England as a whole. Firstly, according to Sweeting (1970, 239) these caves corres­ pond to the fusshohlen, or foot caves, found in tropical karst areas. She considered it likely that the caves were developed under warmer conditions than those of the present, r either during a previous interglacial or, more probably, during the Tertiary. The steep-sided limestone hills, around which the caves are found, were also assigned to the Tertiary by Corbel (1957, 289), who considered them to be Fig. 7.1 The "phreatic network" cares of the Korecambe lay karst Fig, 7*2 Roudsea Yood Care: North \ Cross - sections ROUDSEA WOOD CAVE : SOUTH ( SD333825 ) CRG grade 5B ( modified after Lancaster Cave and Mine Research Society, 1974) metres fig, 7*3 P.oudsea Wood Care: South Fig. 7.4 Nichols Moss Cares Cross - sections BRACKENTHWAITE CAVE ( SD498772 ) CRG grade 4B ( modified after Lancaster Cave and Mine Research Society) 0 10 1________ i _________1 metres Fig, 7.5 3racker.thwaite Cave Cross - sections Elevations 1 Q 2 ^ 3 Ù s HAZEL GROVE CAVE (SD499771 ) CRG grade 4B 0 10 (after Red Rose Cave and Pothole Club & metres Lancaster Cave and Mine Research Society, 1965 and 1970) Fig. 7.6 Eazel Grove Care Pig. 7.7 Hale Moss Cave 118 fossil karst towers similar to those found in tropical regions today. Since the same processes as form karst towers are generally regarded as also having formed tower foot caves, this provides indirect support for Sweeting's thesis. Secondly, Ashmead (1966; 1969a; 1974a, b, c), and subsequently Baldwin (1977), advanced the hypothesis that the caves were formed by solutional attack from the relativ­ ely static estuarine and lacustrine water bodies thought to have existed in the mosses of the area (see 8.3.2) and on the fringes of which all the known "phreatic network" systems are found. According to Ashmead (1966, 19; 1969a, 207), these waters were often peaty and, as a result of their high organic acid content, very aggressive. This meant that the limestone surrounding the mosses was solutionally fretted along the fractures exposed at the limestone-water interface, resulting in a tight network of intersecting solution fissures. These networks diminish in intensity of develop­ ment with distance from the water edge, corresponding to the reduced aggressivity of the waters which resulted from contact with the limestone mass (Ashmead, 1974a , 217-218- 1974b, 22). The caves are almost totally phreatic in nature and the absence of any vadose development was regarded by Ashmead (1974a, 214) as supporting the idea of formation by static water bodies. The caves are horizontally developed, despite their occurrence in beds dipping at up to 25°, as at Roudsea Wood. Furthermore, the vertical development of each system Is restricted to a height range ot 2-3 m (Ashmead. 1974a. 213; 1974b, 19-20; 1974c, 57). These features were taken by Ashmead to indicate the influence of water level 119 control and the absence of structural constraints upon cave formation. Ashmead (1974a, 214) suggested that cave development took place during interglacial phases of high sea level as well as during the Late and Post-glacial period. He argued that the "network" caves originated and evolved by processes integral with the solutional widening of the mosses which they fringe (see 8.3.4). It is likely that the mosses were considerably modified by the action of ice erosion during succes­ sive glacials and that the solutionally dissected moss edges would have been removed by glacial scour (see 8.2.4). It is therefore probable that the processes invoked by Ashmead to explain the "network" caves are post-Devensian in age. Ashmead himself supported this theory in the case of Roudsea Wood Caves which he regarded as having been formed by a pro­ glacial lake dammed in the Leven Estuary (1974a, 218; 1974b, 22). With the Late Flandrian drainage of the mosses, the caves have been abandoned and now lie hydrologically inactive along the moss edges. 7.2.3 The tropical karst hypothesis: discussion The fusshbhlen of contemporary tropical karst areas are characterised by a horizontal, notch-like morphology and a generally smoothly rounded form. The notches tend to be several hundred metres in length along the base of the lime­ stone slopes; they are commonly two to three metres high and vary in depth from one to fifteen metres. Only occasionally do connecting passages extend further into the hills (Paton, 1964; Wilford and Wall, 1965, 52-54; Jennings, 1971, 191; 120 1976, 96; McDonald, 1976, 85). Fusshohlen have been interpreted as the result of a variety of processes at work at the base of karst towers. These include: (i) lateral fluvial solution and corrosion; (ii) solutional surface wash; (iii) spring sapping at the limestone-alluvium contact; (iv) solutional undercutting by swamp waters, by ephemeral lakes at the base of the towers, and by soil moisture; and (v) marine erosion (Lehmann, 1953; Paton, 1964; Wilford, 1964; Wilford and Wall, 1965; Sweeting, 1972; McDonald, 1975; 1976; 1979; Jennings, 1976). Apart from their situation along the base of the limestone hills of the area, the "phreatic network" caves of the Morecambe Bay karst have little in common with the foot caves of tropical karst. They have discrete entrances rather than a notch-like form, the majority of the caves ex­ tend into the hills, and there is no evidence of solution notches anywhere on the cliffs surrounding the mosses (Plate 7.1). 7.2.4 The static water hypothesis: discussion Perhaps the two most significant.characteristics of the "phreatic network" caves are their horizontal nature and their limited vertical extent. These features were regarded by Ashmead as indicative of formation at or near to the water table. Yet the shallow depth of the water bodies in the mosses (see 8.3) would, of itself, have confined Plate 7.1 "Phreatic network" cave entrances, Gilpin Bank Caves (SD4687) 121 solutional attack to a narrow vertical range. More importantly, in many cases the horizontal nature of the caves can be shown to be the result of structural constraints. As may be seen from Fig. 7.8, the majority of the cave systems are either strike-aligned or are in areas of low structural dip. The strike-aligned passages occasionally deviate in orientation somewhat from that of the strike, particularly in the case of Fairy Cave. It is contended that this is the result of joint-control on passage location and hence the preferential development of the joint most nearly aligned along the strike. The orientation diagrams also show an element of dip-control on passage alignment. In most cases these dip-controlled passages are very short and have either been captured by hydrologically more efficient strike passages or act simply as strike passage feeders.

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