Home / Learning / Science Topics / NZ Geology / NZ’s Geological History

NZ’s Geological History

The detailed study of rocks enables us to build up a geological history. The present-day shape of New Zealand above sea level is very different to how it looked millions of years ago.

Gondwanaland – a super-continent that gave us our bedrock

Some hundreds of millions of years ago a super-continent called Gondwanaland existed in the southern hemisphere surrounded by sea. It included the present-day continents of South America, Africa, Australia, India, and Antarctica as well as New Zealand.

Since that time, movement of the Earth’s crust have caused the continents to break away from one another and move to their present positions - a process which is still continuing.

As the continents moved relative to the Earth's poles, the climates changed between cold, temperate and tropical depending on their location.

Between 100 and 80 million years ago New Zealand broke away from Gondwanaland (Antarctica and Australia) and started to move toward its present position. The Tasman Sea was formed, and since that time New Zealand has had its own geological history and developed a unique flora and fauna.

Watch a reconstruction of the formation of New Zealand over the past 65 million years:

Our rocky history

The oldest sedimentary rocks in New Zealand, (remains of which are found in north-west Nelson) were deposited in basins lying offshore from Gondwanaland. Over time, these sediments were disrupted by tectonic movements and pushed up to form land that eventually became parts of Australia, Antarctica, and New Zealand. Later, an extensive series of troughs developed offshore, which collected the sediment eroded from the adjacent continents for nearly two hundred million years. This is how the greywacke rocks that now make up the underlying “basement” and main ranges of New Zealand were formed.

This era came to a close about 110-120 million years ago when tectonic plate movements uplifted these sediments to form new land. A period of calm followed and erosion reduced the mountains to low-lying plains. It was during this time that the split between Australia and New Zealand occurred.

As the land was reduced in height, low-lying swampy areas developed, which are now the sites of our major coal deposits. Eventually the sea started to cover the land, firstly depositing sediments in marginal basins, and later over most of the New Zealand area. Then, about 15 million years ago, the mainly quiet period ended, and New Zealand once again experienced tectonic activity, mountain building and widespread volcanic activity. Several basins developed, filled with sediment, and were uplifted as land.(for example the Manawatu, Wairarapa and Canterbury Plains) and In more recent geological times, the effects of rises and falls of sea level, due to alternating glaciations and warmer intervals, have been superimposed on these tectonic events.

Find out more about New Zealand’s spectacular landforms.

Never-ending change

New Zealand is still in a continuous cycle of geological events, and the level of tectonic activity remains high. Offshore basins receiving sediment may, one day in the future, become land, while other areas onshore, being depressed, will be invaded by the sea. Our great mountains are being continually eroded - piling up debris on their flanks and in the river valleys.

Each major earthquake has a large effect; in 1855 the coastline of Wellington Harbour was uplifted 1.5 metres, and in Napier’s 1931 earthquake about 40 square kilometres of sea bed became dry land.