To the north-east of Mount Taranaki on New Zealand’s North Island is a series of limestone caves filled with dramatic spiky mineral deposits. Around 30 million years ago much of New Zealand was underwater. Over time, however, the calcareous remains of marine organisms were compressed under layers of mud and sand to form sedimentary limestone. Tectonic forces later lifted the rock above sea level to create islands.
Volcanic activity then caused the formation of around 300 limestone caverns now known as the Waitomo Caves. For millions of years, acidic groundwater percolated through the overlying limestone rock and dripped from the ceiling of the caves. This carried mineral deposits out of the rock, which formed the icicle-shaped stalactites that hang from the ceiling. The similar stalagmites that emerge from the ground also developed wherever the drips landed.