Controls on water drop volume at speleothem drip sites: An experimental study

SummaryThe growth of speleothem under cave drip sites is closely related to local climate events and provides an increasingly important means of deciphering past climate change. Since calcite precipitation rates depend on the water discharge at the drip site, the drip rate and mass of water drops detaching from stalactites are fundamental controls on speleothem growth and we have investigated factors that control the volume of water drops in this environment. The classical investigations on the volume of falling water drops are reviewed but there have been no measurements of the volume of drops detaching from curved surfaces equivalent to tips of stalactites. In this study we have used an acoustic drop counting method to measure the variation of the mass of water drops detaching from tubes (representing ‘soda straw’ stalactites) and artificial stalactites with spherical terminations (representing massive stalactites) as a function of tube radius or surface curvature and the drip rate. The experimental method corroborates classical measurements of drop mass detaching from tubes and, for massive stalactites, we derive a simple empirical relationship between drop mass and radius of curvature of a spherical surface, based on 100,000 drop counts from artificial stalactites with 19 different radii ranging from 3.6 mm to 500 mm. The results of this study allow discharge to be calculated from drip interval measurements and provide a quantitative basis for theoretical modelling of speleothem growth from drip sites.