Bulletin of the National Speleological Society - ISSN 0146-9517
Volume 34 Number 4: 129-136 - October 1972

A publication of the National Speleological Society

Minimum Diameter Stalactites
Rane L. Curl


Assuming that stalactites grow into the aqueous space available to them at their tips, it is shown how the pendant drop controls the smallest possible equilibrium diameter of a soda-straw stalactite. By dimensional analysis, it is shown that there exists a characteristic Bond number, Bo = pgd2/s, which determines their diameter. From experiments on drops formed on glass capillary tubes of different sizes, it is found that the Bond number for minimum diameter stalactites is Bo = 3.5. This gives a soda-straw diameter of 5.1 mm under ordinary conditions, agreeing with existing observations. Finally, it is shown that the diameter of a non-equilibrium stalactite should converge, with growth, in an exponential manner to the minimum equilibrium diameter.

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