Zealandia

Zealandia—also called Te Riu-a-Māui in Māori and Tasmantis after the Tasman Sea—is a huge slab of continental crust mostly hidden under the ocean. It sank after splitting from the ancient supercontinent Gondwana between 83 and 79 million years ago. Scientists have labeled it a submerged continent, a continental fragment, or a microcontinent. By about 23 million years ago, it may have been entirely underwater; today, 94% of it lies beneath the Pacific. The largest bits above sea level are New Zealand, followed by New Caledonia.

The name “Zealandia” was coined by Bruce Luyendyk in 1995, and satellite images show it’s nearly as big as Australia. A 2021 study found it’s over a billion years old—roughly twice as old as earlier estimates. Mapping finished in 2023. Covering about 4.9 million square kilometers (1.9 million square miles), it’s far bigger than any other feature called a microcontinent or continental fragment. If classed as a microcontinent, it would be the world’s largest—six times the area of the next biggest, Madagascar, and more than half the exposed land of Australia. It’s more than twice the size of the Ontong Java Plateau (the largest underwater volcanic province) and bigger than Greenland, the Arabian Peninsula, and the Indian subcontinent. Because of its thick crust and other geological traits, some geologists from New Zealand, New Caledonia, and Australia argue it meets all the criteria to be a full continent. As geologist Nick Mortimer put it, if sea levels were lower, it would have been recognized as one long ago.

Zealandia supports major inshore fisheries and holds gas fields, the largest being New Zealand’s Maui gas field near Taranaki. Oil exploration permits were issued for the Great South Basin in 2007. Offshore minerals include ironsands, volcanic massive sulfides, and ferromanganese nodules.

**Etymology** GNS Science recognizes two names. In English, “Zealandia” is a Latin-style name for New Zealand, which itself comes from the Dutch province of Zeeland; it was coined in the mid-1990s and caught on through common use. In Māori, it’s Te Riu-a-Māui, meaning “the hills, valleys, and plains of Māui.”

**Geology** The continent consists mostly of two nearly parallel ridges separated by a failed rift—a graben where the breakup stopped. These ridges rise 1,000–1,500 meters (3,300–4,900 feet) above the seafloor, with a few rocky islands poking above the waves. The ridges are made of continental rock but are lower than normal continents because their crust is thinner—about 20 kilometers (12 miles) thick—so they don’t float as high on Earth’s mantle. About 25 million years ago, the southern part (on the Pacific Plate) began shifting relative to the northern part (on the Indo-Australian Plate). This movement, roughly 500 kilometers (310 miles) along the Alpine Fault, is visible on geological maps and has offset the New Caledonia Basin from its former link to the Bounty Trough. Compression along the boundary pushed up the Southern Alps, though rapid erosion means their height reflects only a fraction of the uplift. Farther north, subduction of the Pacific Plate has driven extensive volcanism in the Coromandel and Taupō Volcanic Zones, while rifting and subsidence created the Hauraki Rift, Whakatane Graben, and Wanganui Basin.

**Volcanism** Volcanism has occurred repeatedly across Zealandia before, during, and after it rifted from Gondwana. Though the landmass has shifted about 6,000 kilometers (3,700 miles) northwest relative to the mantle since breaking from Antarctica, its intracontinental volcanoes have magma similar to those in formerly adjacent parts of Antarctica and Australia. Large-scale eruptions happened in two main periods: the Devonian (370–368 million years ago) and the Early Cretaceous (129–105 million years ago). Volcanism is widespread, but on present-day land it’s mostly low-volume, except for the huge mid-to-late Miocene shield volcanoes that built the Banks and Otago Peninsulas. It also continued steadily in many small areas through the Late Cretaceous and Cenozoic. Some causes are still debated, possibly due to data gaps. In the Miocene, the northern part (Lord Howe Rise) may have slid over a stationary hotspot, creating the Lord Howe Seamount Chain. Some researchers suggest Zealandia played a role in the origin of the Pacific Ring of Fire.

**Geological subdivisions** Scientists sometimes split Zealandia into two regions: North Zealandia (or Western Province) and South Zealandia (or Eastern Province), the latter containing most of the Median Batholith crust. They are separated by the Alpine Fault, Kermadec Trench, and the wedge-shaped Hikurangi Plateau, and they move independently.