Collins New Naturalist Library
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Cave exploration has uncovered archaeological finds which have enhanced our understanding of human evolution, and fossil remains, such as woolly mammoths, which reveal something of the Pleistocene animal world. But perhaps most fascinating of all is the living natural history of caves.There are few unexplored places on earth, but caves still offer countless opportunities for discovery. From new passages to whole new cave systems, significant finds are still being made – recent exploration in South Wales revealed Britain's largest passageways.Caves are formed over many thousands of years, as subterranean waters seep slowly through the crevices of the buckled and twisted laters of limestone rocks. These cracks develop into fantastically shaped passages which stretch for miles, huge caverns housing vast, still lakes and deep potholes through which icy waterfalls tumble. Within them form arrays of stalactites and stalagmites, delicately twirling helictites, slender pillars of calcite and crystal pools. And it is these wonders that have encourages the adventurers who have explored and charted this underground world – descending on ropes into gaping pits, crawling and digging their way along tunnels and diving through freezing torrents to do so.Cave exploration has uncovered archaeological finds which have enhanced our understanding of human evolution, and fossil remains, such as woolly mammoths, which reveal something of the Pleistocene animal world. But perhaps most fascinating of all is the living natural history of caves.The study of cave biology is still in its infancy. Speculation and controversy abound, cavernicolous communities remain under-recorded and new species await discovery in most subterranean habitats. But in this book, Philip Chapman has drawn together his expert knowledge of caves and cave life to present an outstanding and cohesive account of what is now known in this extraordinary world, which for so many has remained unknown for so long.
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The New Naturalist Library
A SURVEY OF BRITISH NATURAL HISTORY
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At or below the water table, the course taken by percolation water is determined by the direction of the hydrological gradient between where the water goes into the permanently-flooded system of cracks known as the ‘phreas’ and where it comes out again as a spring. Within the phreas, water is free to follow along, down or up the 3-D maze of cracks to produce the smoothest possible overall flow. Where the rock beds lie horizontally the smoothest profile may be along just one bed, producing a horizontal cave which may run for several kilometers (Yorkshire has many such systems). Where the rocks dip steeply in a direction which does not coincide with the hydrologically-determined direction of flow, the groundwater may be forced into a series of vertical z-bends, down joints and up the bedding, to tack its way to the spring (a classic example is Wookey Hole in the Mendip Hills). Where the limestone beds are trapped in a syncline or U-bend beneath impermeable rocks, water may be forced to travel down to great depths following the configuration of the rock strata. Chinese geomorphologist Yuan Daoxian has recently reported the discovery of a substantial cave at a depth of 2900 m below the water table in the Sichuan Basin in China. When perforated by drilling, the hole gushed water. Caves at this depth are, however, extremely rare and probably have little or no biological significance.
As the profile of the cave takes shape, under the twin controls of hydrology and geology, the ‘best route’ is inevitably favoured with a greater rate of flow, which promotes more rapid corrosion of its boundary walls – which in turn results in a still greater flow capacity. In this way, the initially diffuse drainage within the limestone is gradually simplified with increasing time (and depth) into a pattern of coalescing collectors of increasing diameter. Over the aeons, the vagaries of geology and hydrology may conspire to favour one particular route in preference over all others, opening it out to form a major trunk conduit which drains the entire subterranean aquifer to its spring, or ‘resurgence’.
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