Where it is and what it carries
The New Hebrides Plate covers about 643,000 km² of the southwest Pacific between New Caledonia and Fiji. It carries all of Vanuatu, a long, Y-shaped chain of volcanic islands. To the west, the Loyalty Islands of New Caledonia sit on the Australian Plate, just across the trench.
The plate is a volcanic arc and the young seafloor behind it. Geologists separate it from its neighbors because the North Fiji Basin, east of Vanuatu, is opening along spreading ridges that cut it off from the plates around Fiji.
The New Hebrides Trench
The Australian Plate sinks east beneath Vanuatu along the New Hebrides Trench. This 1,540 km boundary is the plate’s longest, and relative speeds average about 11.4 cm/yr, ranging from about 9.1 to 12.9 cm/yr. Vanuatu’s earthquakes and volcanoes come from this fast subduction.
Here the sinking plate dips east, the opposite of most western Pacific subduction zones, where Pacific seafloor sinks west. Geologists think subduction once ran the other way, along the Vitiaz Trench to the north, where the Pacific Plate sank southwest. In the late Miocene that system jammed, and a new trench formed on the opposite side of the arc. As the new trench pulled back, the arc swung clockwise and the North Fiji Basin opened behind it.
Midway along the arc, the d’Entrecasteaux Ridge on the Australian Plate jams into the trench next to Espiritu Santo and Malakula, slowing subduction there and lifting the islands.
The back-arc side
East of Vanuatu, the North Fiji Basin keeps opening. Along a spreading ridge, the plate moves away from the Conway Reef Plate at about 8.7 cm/yr on average and up to about 11.8 cm/yr. Farther north it spreads from the Balmoral Reef Plate at about 3 cm/yr. Its northern boundary with the Pacific Plate is slow, about 1.1 cm/yr.
Earthquakes and volcanoes
The dataset lists 233 earthquakes of magnitude 6.5 or larger since 1900, one of them above magnitude 8: the 1920 Vanuatu earthquake (M8.1). An M7.9 quake struck southeast of the Loyalty Islands in 1901, and another M7.9 hit about 99 km southwest of Port-Vila in 1950. In February 2021 an M7.7 quake southeast of the Loyalty Islands generated a small tsunami.
The plate holds 14 volcanoes in the dataset. Yasur on Tanna erupts almost continuously. Ambrym, a broad volcano with a large summit caldera, erupted in 2024, and Ambae’s 2017-2018 eruption forced the evacuation of the whole island. Gaua, East Epi and Lopevi have also erupted since 2000.