Zealandia – the submerged continent

New Zealand – isolated islands or part of a continent?

New Zealand – the country – has a total land area of 268,000 km². Zealandia – the proposed continent – has a land area of 4,920,000 km²! This huge area of land is about three-fifths the size of Australia. On the surface, Zealandia does not look like a continent because 94% of it is covered by the Pacific Ocean. But when you look at a bathymetric map of the area and consider some of Zealandia’s features, the proposal for it to be called a continent becomes more convincing.

What makes a continent a continent?

Geologists define a continent as a major land mass, including both dry land and the continental shelves that lie off the coast. A continent is made of continental crust – a base of igneous, metamorphic and sedimentary rocks. (Oceanic crust is made up of basalt and is thinner and denser than continental crust.) A continent should also have areas of high elevation when compared to the surrounding seabed. What isn’t defined is size – there is no minimum size requirement for a continent.

Zealandia meets these definitions. It is a continuous expanse of continental crust, linked together by the islands of New Caledonia to the north, North, South and Stewart Islands (Te Ika-a-Māui, Te Waipounamu and Te Punga o Te Waka a Māui), the Auckland Islands and Campbell Island to the south and the Chatham Islands to the west. Zealandia’s continental crust is physically separate from Australia’s continental crust. Zealandia is also significantly elevated, rising about 3,000 m above the surrounding oceanic crust.

Putting the pieces together

The unusual underwater geography that surrounds New Zealand has intrigued geologists for more than a century. Information gathered from satellite measurements and from seafloor sediment cores work a bit like puzzle pieces, helping scientists develop clearer pictures of the area.

If we could pull the plug on the world’s oceans, it would be quite clear that Zealandia stands out.

Dr Nick Mortimer, GNS Science

The American geophysicist and oceanographer Bruce Luyendyk introduced the name and the concept of the submerged continent Zealandia in 1995. New Zealand scientists Nick Mortimer and Hamish Campbell advanced the idea with their 2014 book Zealandia: Our Continent Revealed. However, it was their paper Zealandia: Earth’s Hidden Continent that propelled Zealandia onto the world stage. The New Zealand Herald reports that the paper “instantly captured the world’s imagination, generating more than 16,000 news articles that reached nearly a billion people”.

Although it caught people’s attention, Zealandia is not likely to appear on world maps any time soon. There is no group that officially names continents. Internationally, people can’t even agree if there are five or seven continents, so at the moment, agreeing to eight seems unlikely. Dr Mortimer says, “Supporters will have to continue using the term and hope it catches on.”

Pangaea, Gondwana and Zealandia

Scientists have learned a huge amount about plate tectonics and continental drift over recent decades, and it has changed some of our thinking about the world. The general understanding is that all land on Earth was once part of a supercontinent called Pangaea, which later broke up into Laurasia and Gondwana. Gondwana continued to move and separate into the more recognisable land masses we see around us today.

About 85 million years ago, as the seafloor spread, Zealandia broke away from Australia. Initially, Zealandia was all land, but as it moved and was stretched, much of it sank beneath the sea. Then the plate tectonic movements changed direction, and instead of moving away (extending), the plates started to collide. New Zealand began to be pushed up above sea level while most of Zealandia remained submerged.

Update

In January 2020 newly published results from expedition #371 explained how two violent tectonic events shaped the Zealandia continent and also why this continent is so different to others.