Rocky wonderland

Some would say it has taken 25 million years, but Waitaki has finally been declared New Zealand's first Unesco Global Geopark

- ERIC TRUMP

New Zealand is at once young and volatile, ancient and settled. Its surface cracks and steams with earthquakes and geothermal springs, bubbles and boils with volcanoes and mud pools.

On the other hand, this is old country. New Zealand, with New Caledonia, the Chatham Islands and a few others, are peaks of sunken Zealandia, Te Riu-a-Māui, Earth's most recently recognised continent. Zealandia is 94% under water, half the size of Australia, and a billion years old.

Zealandia began as a thin strip of land joined to the eastern slopes of Gondwana, the ancient Southern Hemisphere supercontinent. About 80 million years ago, it gradually undocked from what would become Australia, unzipping the Tasman Sea and rafting northward from its birthplace in the Antarctic Circle into the ancestral-Pacific. For the next 40 million years or so, in a process called thermal subsidence, Zealandia stretched and cooled, losing buoyancy to such an extent that it almost entirely sank beneath the water.

Its land area was at a minimum 23 million years ago, during the Duntroonian geological stage of maximum marine inundation, the "Oligocene Drowning". Imagine Central Otago and Fiordland as part of an archipelago in a warm sea. Beginning at the same time, a new boundary formed between the Australian and Pacific tectonic plates. Their grinding together lifted and continues to lift New Zealand, thrusting the Southern Alps upward 10 to 20 millimetres a year.

One shallow seabed that was blanketed in millions of years of greensand, mud, and marine snow - those expired sponges, coral, diatoms, plankton and sea urchins that drifted down to form limestone - was in the Waitaki District. This stunning, 7214sq-km porthole into New Zealand's watery past straddles the border between Otago and Canterbury and stretches from the Pacific almost to the Southern Alps.