How does flowstone form on cave walls and ledges?

Flowstone forms when water containing dissolved minerals—most commonly calcium carbonate—flows in thin films along cave floors, ledges, or down sloping walls.12

The process begins as rainwater infiltrates the soil, absorbing carbon dioxide to form a dilute carbonic acid. This acidic water dissolves calcite from the surrounding limestone bedrock as it percolates downward. When this mineral-rich water emerges into the cave environment, it releases its dissolved carbon dioxide into the cave atmosphere. This loss of carbon dioxide reduces the water's ability to hold the minerals in solution, causing the calcite to precipitate out and build up in layers.213

While flowstone is typically white or translucent, it often appears in shades of tan, orange, or brown due to the presence of iron oxides or humic substances—organic products of plant decay—carried in by the water. These deposits are a type of speleothem, and their growth rate is highly variable, depending on factors such as seasonal flow rates and the concentration of carbon dioxide.123