Macroholes in stalagmites and the search for lost water

Abstract

Fluid microinclusions in stalagmites have provided samples of paleowaters present during the growth of the stalagmite, but only in microliter amounts. Genty et al. (2002) discovered much larger water‐filled macroinclusions in some stalagmites. Using computerized tomographic (CT) X‐ray‐scanning and magnetic resonance imaging (MRI) we searched for such macroinclusions in 21 stalagmites from diverse localities in North and Central America and the Caribbean. We show that most stalagmites contained numerous mm to cm‐sized internal cavities (macroholes). These do not penetrate the outer surfaces which in most cases are deceptively unblemished. Some stalagmites have up to 10% average internal porosity. Two types of macroholes are distinguishable: axial holes formed during growth due to slower calcite accumulation at the axial drip site; off‐axis holesformed penecontemporaneously with growth in discrete layers; these cut previous growth laminae showing that they are post‐depositional. Using MRI on uncut, apparently sealed specimens, we find that very few of these cavities contain significant quantities of water although they were clearly formed while the stalagmite was being continuously bathed by drip water. Presumably, the water has escaped post‐depositionally, through micro fissures, extensive connected hole system, crystal boundaries or other defects.