Cave Development in the Limestone of the Ingleborough District

Abstract

Situated in North-west England, Ingleborough is near the centre of an area of 300 square kilometres of well-known karst topography (see Fig. 1). The limestone caves of the area are well known and were described in detail by Dr. M. M. Sweeting in the Geographical Journal of March 1950 (Sweeting, 1950). Over the last decade major improvements in caving equipment and standards have permitted much more detailed study and survey of the caves, particularly with regard to the geological features. In 1950, the information on the caves appeared to show that they occurred in a series of three well marked, narrow, horizontal zones, and Sweeting proposed that the caves were formed at a lowering series of water tables. However, recent evidence demonstrates that geological controls within the sub-horizontal limestones have been more important and the chronology of the caves only indicates a preglacial phreatic phase and a post-glacial vadose phase.x Throughout the world the environment for the formation of limestone caves has been ascribed to all three zones of karst groundwater (as defined by Cviji<5, 1918). An origin under vadose conditions, where the cave stream does not fill the passage but has an air surface above it, was postulated for the Yorkshire caves as early as 1907 by Dwerryhouse. Formation of caves at the water-table was argued by Swinnerton (1932), who suggested that maximum erosion should take place at the level where there was the greatest confluence of groundwater, and this theory was applied to the Yorkshire caves by Sweeting in 1950. The phreatic zone, at a greater depth where all cavities are filled with water and the flow is only under hydrostatic pressure, was claimed to be the environment of main cave development by Davis (1930) and Bretz (1942), but this theory has not previously been adopted for the caves of the Ingleborough region. The second of these theories?the water-table theory?is now complicated by the recent recognition of the fact that a water-table in the classical sense does not exist in cavernous limestones (Drew, 1966), such as the Carboniferous in the Ingleborough area. These basically non-porous limestones contain their groundwater in discrete channels, or caves, and there is no clear boundary between a zone of percolating groundwater, above a water-table, and a lower zone of water-filled cavities. Instead it is common to find dry caverns below surface rivers or other cave passages containing streams; the Gaping Gill cave is a good example for all three of its subsidiary entrance systems containing active streams, Stream Passage, Disappointment and Flood Entrance Pot-holes, are at some place vertically above the large dry passages of the lower, main, series. Any attempt at delimiting a conventional water-table in such an area results in a three dimensional surface so complex as to be valueless.z Detailed morphological studies of the cave passages in the Ingleborough district show that the various cave systems include examples of both phreatic and vadose origin.