Rimstone Pools


Rimstone pools with coloured light. Grotte de Saint-Marcel d`Ardèche, France.
The most famous Rimstone Pools of the world in ShowcaveSkocjanske Jame in RegionSlovenia. This pools are dry, so they are inactive.

Rimstone Pools are formed by water flowing down a slope, a very thin layer of water on a rather big area has a large surface. Because of the large surface the water looses carbon dioxide (CO2) to the atmosphere of the cave and as a result calcite precipitates. The water forms tiny waves as it flows, which are triggered by irregularities in the surface of the rock. The precipitated lime, which forms a thin skin on the surface of the water, is shaped into arches by these waves. Thus, the first shallow arch-shaped pools are formed, filled with the dripping water.

As the lime precipitation continues, the precipitated lime skin is always transported by wave movements of the water to the edge of the basin, which continues to grow. This explains why the pool always grows on its edge. No calcite is deposited on the bottom. Very typical are pools with a depth of several decimetres to metres and edges that are only a few centimetres or decimetres thick. In active pools, the water flows from one pool to the next. The water is clear; if there were larger amounts of sediment, the basins would be filled with sediment until basins have become steps or plateaus. The most beautiful pools therefore form in side passages in relatively small tributaries. In river caves they are only formed when the cave river transports no or little sediment even in times of high water. If the inflow is blocked, the pools often hold the water for a very long time, they are watertight and with the high humidity the water hardly evaporates either. But at some point they are dry and are called inactive or fossil.

Sinter basins are called speleothems or cave minerals, they are formed in karst caves. Since they are formed by the precipitation of limestone, they only occur in carbonate karst. Among the various stalactite forms in karst caves, they are rather rare; both the gradient must be right and the water must be clean. The conditions of formation are relatively closely to the conditions that lead to the formation of Speleothemcave pearls, as a result there are sometimes shallow rimstone pools with cave pearls.