Where it is and what it carries
The Bird’s Head Plate is a microplate of about 526,000 square kilometers, or 0.1% of Earth’s surface. It carries the Bird’s Head Peninsula of western New Guinea, Cenderawasih Bay, the island of Biak and, to the west, Halmahera and the North Maluku islands. In all it holds about 7.8% of the land of Indonesia. Its crust is mixed: the peninsula is a fragment of Australian continental crust, Halmahera is a volcanic arc and the surrounding seas are oceanic.
Like the other microplates of eastern Indonesia, it is debated. Geologists separate it because GPS measurements show the Bird’s Head moving quickly relative to the Australian Plate rather than riding along with it. Its exact boundaries are still being refined.
What happens at its edges
The plate has eight neighbors. On the north, the Caroline Plate subducts beneath it at the New Guinea Trench along 765 km, at about 2.2-2.8 cm/yr, and a 389 km subduction boundary with the Philippine Sea Plate moves at about 1.5-2.2 cm/yr.
The western and southern edges are faster. The boundary with the Banda Sea Plate, 800 km long and mostly subduction, moves at about 6.5-7.7 cm/yr. The 479 km boundary with the Molucca Sea Plate mixes subduction and strike-slip at about 8.6-10.1 cm/yr, and the short boundary with the Sunda Plate moves at about 10.7 cm/yr.
To the east, a 548 km boundary with the Maoke Plate moves at about 8.0 cm/yr along rift and strike-slip faults. Short boundaries with the Australian Plate (132 km, about 9.3 cm/yr) and the Woodlark Plate (54 km) complete the ring. Across the north of the Bird’s Head runs the Sorong Fault, a major strike-slip zone along which slivers of crust have moved westward.
Earthquakes and volcanoes
The dataset lists 70 earthquakes of magnitude 6.5 or larger on the plate since 1900, two of them magnitude 8 or more. Both struck near Biak: the 1914 Biak earthquake (M8.2) and the 1996 Biak earthquake (M8.1), which caused a destructive tsunami. Other large events include a 1979 earthquake south of Biak (M7.9) and the 2009 earthquake near Manokwari (M7.7).
The plate holds 13 volcanoes in the dataset, nearly all in the Halmahera arc. Gamalama forms the island of Ternate, and Dukono on northern Halmahera has erupted almost continuously for decades. Ibu, Gamkonora and Kie Matubu on Tidore are other examples.