Cavers have been actively exploring caves in the Waitomo area since the 1940's. By the early 1950's caving had emerged as a significant recreational pursuit. By the late 1970's many of Waitomo's major caves were discovered and explored, surveyed, mapped and documented. This "golden era" of Waitomo caving resulted in the discovery of many kilometres of new caves and scientific discoveries.
A number of these caves are now used for blackwater rafting, adventure caving and cave abseiling. They also provide valuable information about past climate, landscapes, flora and fauna and cultural history. Their relatively stable climatic conditions have protected fossils, sub-fossil bones, silts, mud, and traces of human usage.
Numerous caves in the Waitomo area are renowned for their Speleothems or "formations", and "decorations". The basic types are stalagtites, stalagmites and columns, which form as a result of water dripping from the roof of the cave or flowing over the exposed limestone walls. As the water flows down through the earth towards the cave roof and walls, it dissolves limestone in its path. This limestone is then left as a crystalline deposit within the cave. These spectacular formations develop over hundreds and thousands of years and must be treated with respect.
It has been estimated that it takes about 100 years to form 1 cm3 of stalactite. They are very delicate and can be severely damaged simply by the touch of a human hand.
Most speleothems are composed of calcite (calcium carbonate) formed from the limestone rock. As water slowly percolates through the limestone it is dissolved and re-deposited around the edge of a drop of water clinging to the roof. A tiny ring of calcium carbonate (calcite) the diameter of the drop is formed. As more calcite is deposited, the stalactite grows.
The drop forms a near-transparent, crystal white ring. Then, as the ring grows it creates a delicate straw form. These are the beginning stages of stalactites. In time, the hollow tube becomes blocked and water runs down outside the tube forming thicker tapering stalactites. Others remain straw-like and very delicate. Drips falling from stalactites hit the ground and form stalagmites. When a stalactite and stalagmite "grow" towards each other and eventually meet, a pillar or column is formed. The Pipe Organ formation in the Glowworm Cave is a substantial column, 2.5 meters high and 7 meters in circumference, and is said to be about 750,000 years old.
Speleothems such as "curtains" or "drapes" develop in a similar way, except that the calcium carbonate solution runs down the wall of the cave depositing thin layers of calcite that build up layer upon layer. Flowstones occur where super-saturated solutions flow over cave walls, and rimstone or gour pools form with the deposition of calcite as dams. Other speleothems, such as crystal forms, are the result of evaporation and yet others, such as "cave pearls" are concretions formed around small pebbles or gravel.
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