The Geology of Waitomo

A limestone landscape

There are around 300 known limestone caves that lie beneath the hills of the Waitomo region. Geological and volcanic activity created the caves which have evolved over the last 30 million years.

THE FORMATION OF LIMESTONE

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The limestone that visitors see in the Waitomo Glowworm Caves was formed about 30 million years ago when the region was beneath the sea. Limestone is a fossil rock made up of the remains of millions of marine animals, which were broken down by the sea into tiny particles that slowly settled on the seabed. Over millions of years, layer upon layer of these shell particles piled thickly on the seabed and were eventually compacted to create limestone. In some areas of Waitomo the limestone is over 200 metres thick.

THE BEGINNING OF THE CAVES

Limestone layers, Waitomo Glowworm Caves

Over the last 30 million years, the area we now know as Waitomo was formed as a result of geological and volcanic activity. Through this earth movement much of the hard limestone beneath the sea buckled and bent and rose up out of the water. Exposed to the air, the limestone separated into huge blocks of rock, filled with cracks and weaknesses. These cracks created tiny channels through which water could flow and over millions of years larger caverns were eventually formed.

HOW CAVE DECORATIONS DEVELOP

Once the caves were formed, stalactites, stalagmites and other cave decorations began to grow. Water dripping from the roof or flowing over walls leaves behind a deposit of limestone crystal which sets as hard as concrete. As time passes, these accumulate to form beautiful cave decorations. Stalactites grow down from the ceiling and stalagmites grow up from the cave floor. If they join together they are called columns or pillars and where they spiral around they are called helicti.

Cave decorations can take hundreds of years to form. As an indication, a stalactite grows an average of one cubic centimetre every 100 years.