Bulletin of the National Speleological Society - ISSN 0146-9517
Volume 25 Part 2: 45-65 - July 1963
A publication of the National Speleological Society
The Development of Karst
Alan D. Howard
Karst landforms may be considered to be largely composed of three features, cutters, sinks, and caves. These are interrelated and transitional between each other.
Cutters are solutionally enlarged joints. They are normally filled with a residual terra rosa, and form beneath such a soil cover. Cutters are a distinct karst landform, although they are often difficult to recognize because they may be obscured by the soil material. Cutters generally are not remnants of former caves. Where cutters are the dominant karst landform, joint solution generally decreases uniformly downwards. This solution is directly related to present topography in depth, intensity, and directional development. Cutters are normally developed into a crude, dendritic network similar in directional development to the overlying topography. Cutters originate through solution by ground water flowing laterally within the enlarged joints. This is a gravity flow under a gradient. The amount of development of cutters depends upon the climate, the rock properties, such as solubility and grain size, and the geologic-topographic situation.
Cutters are the only karst form present in completely homogeneous soluble rock. Under such conditions they are an equilibrium feature of the landscape, and they have a simple form that changes little with time. Where the rocks are heterogeneous, such as in area of associated soluble and non-soluble rocks, the greater will be the extent of development of sinks and caverns, and the cutter will be less prominent.
Cavernous passages result from soluton of the bedrock by through-flowing groundwater. Because of the necessity for continuous addiiton and removal of groundwater in order for cavernous channels to form, caves are continuous conduits leading from a source of groundwater to a groundwater exit. No one theory of cave development or sequence of cave-forming events can be common to all caves. Every cave has a unique history, but nevertheless thate are certian broad principles which are true of the development of all caves. Cave appear to fall into two classes, those that arise through solution and abrasion by free-surface groundwater streams flowing with a definite gradient, and those that result by soluiton by groundwater flowing under artesian pressure. Some caves have records of both processes having acted at different times.
Caves result from the presence of a favorable geologic situation (stratigraphy and structure). Both the geology and the geologic effects upon topography are factors which control the development of caverns. In order to completely describe the origin of a cave, the specific geologic-topogrphic relationship which promoted its development must be specified.
Sinks are enclosed topographic depressions which are collection areas for the diversion of surface water underground. Sinks presuppose caverns, but the reverse is not necessarily true. Most sinks derive their topographic form from the coninuous removal of soil material underground, and the sink landform is usually a structure of the soil mantle only, for the bedrock surface does not usually have an associated funnel shape. Only a few sinks originate from the collapse of cavern roofs, and even these are perpetuated by continuous dowward removal of increeping soil material.
Caves and sinks are most common in areas of great inhomogeneities of geology. In contrast to the rather static and monotonous topographic forms prevailing in areas of homogeneous rock, the topography in areas of great diversity of geology is generally varied and typically in a state of flux. Such conditions, which are the result of the influences of various lithologies and structures upon the topography, are often conducive to the development of caves and sinks when soluble rocks are present.
Because caves result from the effects of stratigraphy and structure upon topography, neither uplift nor peneplanation is called upon as a direct causal agent for the development of caves.
Cutters are also found in areas of diverse geology, but are persent in inverse proportion to the degree of diveristy. In such areas cutters will have various forms, and these may approach that of caves.
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