Abstract - Cave Volume from Breathing Phenomenon at Wind Cave National Park

Schnute, Jon T. 1963. Cave Volume from Breathing Phenomenon at Wind Cave National Park, A Proposed Study. Summer 1963, unpublished document, Physical Science office files, Wind Cave National Park, 6 p.



This report summarizes a method for determining the volume of Wind Cave by means of wind, barometric and temperature measurements at the entrance. The following assumptions are made:

(a) Wind leakage through the elevators and the natural entrance may be stopped, and, when this is done, the entire wind from the cave may be accounted for in the man-made entrance. Implicit here is the assumption that the only cave entrances are those presently known. (If this assumption is violated, the resulting figure for cave volume will be too small.)

(b)When wind is not detectable at the entrance, the cave and atmosphere are at true equilibrium. Actually this may not always be true. An abrupt change from increasing to decreasing air pressure (or vice-versa) may lead to a short period of no wind, even though the internal pressures have not balanced. This will be described in detail later. Such difficulties are particularly likely if a very constricted passageway is the only entrance to a large room, or if a large number of constricted passageways account for a significant volume of the cave. (In such a case the cave volume would again be computed too small, but the resulting volume figure would be more in line with accessible passageway.)

{c) The cave temperature is constant, and, over a given period of data readings, the entering (emerging) air has constant temperature. One need not assume that the entering air is at cave temperature. (Violation of this assumption leads to insignificant change in results, as temperature change accounts at most for a small percentage of wind.)

d) At times when the cave is in equilibrium, the pressure is the same at every depth. This assumption is, of course, strictly false. The ordinary altimeter illustrates the important pressure-depth relationship. However, pressure changes due to depth are very small, since depth changes are at most a few hundred feet. Furthermore, pressure distributions are similar at any equilibrium time.

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