Australian Plate
The Australian Plate is the 6th-largest of the 52 plates in the PB2002 plate model, covering 46.0 million km² (17.8 million sq mi), or 9.0% of Earth’s surface. Australia, southern New Guinea, the western side of New Zealand, New Caledonia, Fiji and the eastern Indian Ocean floor.
- Area
- 46.0 million km² (17.8 million sq mi)
- Share of Earth’s surface
- 9.0%
- Speed across the plate
- 3.3 to 7.1 cm a year (1.3 to 2.8 in)
- Direction at its center
- Toward the north-northeast
- Length of its edges
- 36,890 km (22,920 mi)
- Neighboring plates
- 18
- Edges by type
- 31% convergent · 42% divergent · 27% transform
- Volcanoes on it
- 13 active in the past ~12,000 years
What happens at its edges
It is one of the fastest-moving plates that carries a continent, heading roughly north-northeast. Along its northwestern edge it sinks beneath the Sunda Plate at the Sunda Trench off Sumatra and Java, a source of large earthquakes and the volcanoes of Indonesia.
In New Zealand the boundary with the Pacific Plate runs through the South Island along the Alpine Fault. Many maps join this plate and the Indian Plate as one Indo-Australian Plate; measurements show they now move separately.
How fast it moves, and which way
At its center (30.0°S, 122.6°E) the Australian Plate moves about 6.9 cm (2.7 in) a year toward the north-northeast. Because a plate turns around a pole rather than sliding in a straight line, the speed changes across it: from 3.3 cm (1.3 in) a year to 7.1 cm (2.8 in) a year, with an area-weighted average of 6.3 cm a year. That average makes it the 14th fastest of the 52 plates.
These figures are measured against the average motion of all the plates together (the “no-net-rotation” frame), which is how plate speeds are usually quoted. Measured against the Pacific Plate instead, the Australian Plate moves about 9.0 cm (3.6 in) a year toward the northeast at its center.
In the model it rotates about a pole at 33.3°N, 33.4°E at 0.640° per million years. The speeds are averages over years to millions of years of measurement; earthquakes move the ground near a boundary in sudden steps instead.
Neighboring plates and boundaries
Its edges run for 36,890 km (22,920 mi): 31% convergent, where plates move together; 42% divergent, where they move apart; and 27% transform, where they slide past each other. It sinks beneath the Pacific Plate, Sunda Plate, New Hebrides Plate and Burma Plate at subduction zones.
| Neighbor | Shared edge | Boundary types | Relative speed |
|---|---|---|---|
| Antarctic Plate | 11,150 km (6,930 mi) | Divergent 67% · Transform 33% | 6.8 cm a yearup to 7.2 cm |
| Pacific Plate | 4,280 km (2,660 mi) | Convergent 66% · Transform 34% | 5.2 cm a yearup to 9.8 cm |
| Indian Plate | 3,600 km (2,240 mi) | Convergent 64% · Divergent 29% · Transform 6% | 0.5 cm a yearup to 1.1 cm |
| Sunda Plate | 3,290 km (2,050 mi) | Convergent 100% | 5.8 cm a yearup to 6.9 cm |
| Somali Plate | 3,150 km (1,950 mi) | Divergent 56% · Transform 44% | 4.0 cm a yearup to 5.0 cm |
| Kermadec Plate | 2,220 km (1,380 mi) | Divergent 82% · Convergent 10% · Transform 8% | 2.6 cm a yearup to 5.9 cm |
| Woodlark Plate | 2,210 km (1,370 mi) | Divergent 48% · Convergent 29% · Transform 24% | 2.2 cm a yearup to 4.0 cm |
| New Hebrides Plate | 1,540 km (960 mi) | Convergent 88% · Transform 7% · Divergent 6% | 11.4 cm a yearup to 12.9 cm |
| Timor Plate | 1,450 km (900 mi) | Transform 41% · Convergent 30% · Divergent 29% | 2.1 cm a yearup to 2.9 cm |
| Conway Reef Plate | 850 km (530 mi) | Divergent 70% · Transform 22% · Convergent 8% | 2.9 cm a yearup to 5.5 cm |
| Maoke Plate | 660 km (410 mi) | Transform 100% | 1.3 cm a yearup to 1.3 cm |
| Tonga Plate | 560 km (350 mi) | Divergent 99% | 5.5 cm a yearup to 9.3 cm |
| Niuafo’ou Plate | 550 km (340 mi) | Divergent 68% · Transform 32% | 8.3 cm a yearup to 9.2 cm |
| Balmoral Reef Plate | 500 km (310 mi) | Transform 80% · Divergent 12% · Convergent 8% | 6.9 cm a yearup to 6.9 cm |
| Banda Sea Plate | 350 km (220 mi) | Divergent 67% · Transform 33% | 1.2 cm a yearup to 1.5 cm |
| Futuna Plate | 250 km (160 mi) | Transform 100% | 3.5 cm a yearup to 3.5 cm |
| Burma Plate | 160 km (100 mi) | Convergent 100% | 5.1 cm a yearup to 5.3 cm |
| Bird’s Head Plate | 130 km (80 mi) | Divergent 58% · Transform 42% | 9.3 cm a yearup to 9.3 cm |
Relative speed is how fast the two plates move against each other along their shared edge, averaged over its length.
Countries and territories on the Australian Plate
7 lie entirely on it; the other 4 are split between plates. The share is the part of each country’s land on this plate.
- Australia all
- Papua New Guinea about 34%
- Indonesia about 8%
- New Zealand about 38%
- Fiji all
- New Caledonia all
- Indian Ocean Territories all
- British Indian Ocean Territory about 87%
- Norfolk Island all
- Ashmore and Cartier Islands all
- Coral Sea Islands all
Volcanoes on the Australian Plate
The Smithsonian Global Volcanism Program lists 13 volcanoes on this plate that have been active in roughly the past 12,000 years. The most recent eruptions on record:
- Tongariro New Zealand, 2012
- Ruapehu New Zealand, 2007
- Sessagara Hills Papua New Guinea, 1944
- Taranaki New Zealand, 1800
- Nabukelevu Fiji, 1660
- Taveuni Fiji, 1550
Where the edges are blurred
Parts of this plate lie in the New Hebrides-Fiji and Ninety East-Sumatra zones, which the model marks as broad belts of deformation rather than sharp plate edges. There the motion between plates is spread over many faults, and a single boundary line is a simplification.
Sources
Outline, area, boundary types and motion: Bird, P. (2003), An updated digital model of plate boundaries, Geochemistry Geophysics Geosystems, 4(3), 1027, doi:10.1029/2001GC000252. Released by its author into the public domain (CC0 1.0). Areas are the model’s published figures; speeds, directions, boundary lengths and countries are calculated from its outlines, boundary steps and rotation poles.
Volcanoes: Global Volcanism Program, Smithsonian Institution, Volcanoes of the World (v. 5.4.0). Country outlines: Natural Earth.