Clifden Caves

The local bedrock here is a limestone rich sediment that was deposited in a shallow sea environment as an accumulation of broken up shells and bryozoa (sea mosses). The Clifden Limestone dates from a time when almost all of Zealandia was covered by sea. Its companion limestones, slightly older, can be seen at Punakaiki, Waitomo and indeed across many parts of New Zealand.Since that time (about 20 million years ago) the whole region (in fact most of New Zealand) has been uplifted above sea level due to collision along New Zealand’s plate boundary. Limestone is predominantly made of calcium carbonate, which is susceptible to being dissolved by slight acidity in groundwater. Over long time-spans this can lead to the opening of cracks in the bedrock and the creation of passageways and tunnels that are conduits for underground streams. In places, the dissolved calcium carbonate can get re-deposited by dripping water on the walls and floor of the cave to form a wide variety of formations such as curtains, stalactites (hanging down), stalagmites (growing upwards), straws and pillars.

It is worth taking your time to look at the features in the cave as you move through its passageways (expect 1 - 2 hours). See how many different formations you can identify and also switch off your lights in some of the bigger chambers to spot the glowworms. The limestone itself is quite smooth and featureless. Only sometimes can you see fossil outlines. In places in the cave layers of cemented pebbles are present. These are 'glued' to the cave wall and are not part of the limestone formation. You can imagine them being laid down by an underground stream in the cave, and then cemented. Why do you think some of the passages are dry if they have been created by water?