The NSS Bulletin - ISSN 1090-6924
Volume 51 Number 2: 100-110 - December 1989

A publication of the National Speleological Society

Features of the Genesis of Jewel Cave and Wind Cave, Black Hills, South Dakota
Derek C. Ford

Jewel Cave and Wind Cave, South Dakota, are here interpreted as multi-storey dissolutional mazes created during the present erosion cycle by deep phreateic waters that ascended through them. They formed where such groundwaters were focused to discharge through weaknesses in an overlying sandstone formation. The multi-storey structure is created by occurrence of different joint systems in adjacent beds or greater units, with inter-storey blocking layers such as thin clays often playing a role. In such structures, lower storeys tend to be more extensive; upper storeys may contain both outflow and adventitious components. Mixing corrosion effects and migration of springs can complicate upper storeys. As such caves drain, condensation corrosion facets and pockets may be created. From U series dating and magnetic studies of normal speleothems and of subaqueous calcite encrustations, Jewel Cave drained more than 350,000 years ago. Its characteristic subaqueous spar sheets are certainly older than 1,250,000 years and probably greater than 2,500,000 years in age. Wind Cave has drained with the past 500,000 years or so. The mean rate of fall of the watertable in it is ~0.375 m per thousand years but the actual rate of fall has varied probably in response to Quaternary climatic fluctuations. Studies of stable isotope ratios indicate that the subaqueous deposits were precipitated from waters warmed to a probable range, 15-50°C. It is most likely that such waters were responsible for excavating the bulk of the caves as well, although there are older paleokarst remnants locally; thus genesis of the caves is to be attributed to the type and scale of thermal waters that feed the present hot springs in the Black Hills. Combinations of several different factors may account for the differing form, thickness and depth of deposition of the subaqueous calcites, including regulation of the rate of de-gassing by presence of caprocks.

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