Journal of Cave and Karst Studies - ISSN 1090-6924
Volume 65 Number 1: 43-52 April 2003

A publication of the National Speleological Society

Gypsum wedging and cavern breakdown: Studies in the Mammoth Cave System Kentucky
William B. White and Elizabeth L. White

Abstract

Many segments of dry passages in the Mammoth Cave System contain an unusual breakdown lying unconformably over underlying stream sediments. The association of many of these breakdown areas with sulfate minerals (primarily gypsum) suggests that crystal wedging and replacement of limestone by gypsum are important factors in this type of cavern collapse. The following features are characteristic of mineral-activated breakdown: 1) Walls and ceilings fractured in irregular patterns often with visible veins of gypsum following the fractures; 2) Breakdown consisting of characteristic thin, irregular splinters and shards of bedrock; 3) Curved plates of bedrock ranging in size from a few centimeters to more than a meter hanging from the ceiling at steep angles and cemented only by a thin layer of gypsum; 4) Collapses that take the form of symmetrical mounds with coarse irregular blocks at the base grading upward into a rock flour at the top. Thin sections of the curved plates clearly show gypsum replacing limestone. Possible sources for the sulfate-bearing solutions are from the weathering of pyrite either at the top of the overlying Big Clifty Sandstone or in the limestone wall rock surrounding the cave passage. Reactions of the percolating solutions produce sulfate minerals in the wallrock adjacent to cave passages. Gypsum and other sulfate minerals created in the wall rock are less dense than calcite and exert sufficient pressure to spall off bits of the rock, some of which remain cemented in place by the gypsum.

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