Ruakuri Cave

Karst develops in water-soluble rocks, typically limestones and these occur in numerous localities throughout New Zealand. Limestone is a sedimentary rock with a high percentage of calcium carbonate (CaCO3) and a low percentage of sand and mud. Relatively pure, hard limestones with the highest percentage of calcium carbonate dissolve most readily and produce the best caves and karst features. Waitomo is one of the main districts in New Zealand for finding caves and karst and Ruakuri Cave is one of the most visited by tourists.
Caves are an essential feature of karst environments because they provide the fundamental conduits of the subterranean drainage system. Over thousands of years the water percolating through networks of cracks in limestone rocks creates larger and larger cavities. It eventually forms a labyrinth of caves along which water can flow freely from recharge to discharge point. As cave systems evolve and conditions change, water may no longer flow through them – they may flood only occasionally or passages may become completely dry if cave streams descend or dissolve to lower levels within the karst.
Caves may develop spectacular speleothem features such as stalactites that hang down from the ceiling and stalagmites that grow up from the floor. The solution of carbonate rocks like limestone and marble in water forms curious karst features both above and below ground. This process involves a series of chemical reactions between water (H2O), carbon dioxide (CO2) and calcium carbonate (CaCO3).
The combined reactions can be summarised in the following equation:
water + carbon dioxide goes to carbonic acid which reacts with limestone to give more soluble calcium bicarbonate.
These reactions also occur in reverse in a process called precipitation. In this situation, percolating waters high in dissolved bicarbonate reach an existing cave where the air pressure and temperature may be different from the surface. Carbon dioxide is released from the calcium bicarbonate leaving calcium carbonate that crystallises into stalactites, stalagmites and precipitates such as flowstone in caves.

Can you tell the difference between stalactites and stalagmites? Can you see the cracks in the ceiling where the water flows through and down into the cave? Straws are just a special kind of stalactite or stalagmite?
The path follows wooden balconies and high-level dry caverns, where has all the water gone?
Ruakuri Cave is used for blackwater rafting can you hear or see a party passing through beneath you? Which way is the water running?