Geology of The Pacific Ocean - Geological Origins of The Pacific Islands

Geological Origins of The Pacific Islands

The theory of plate tectonics, which is supported by seismology, volcanology, gravimetry, and paleomagnetism (remanent magnetism), explains the origin of the physical features of the Pacific. The islands of the Pacific have developed in a number of ways. Some have originated as chains of volcanic islands on the tectonic plates either as a result of mantle plumes or by fracture propagation. Atolls have developed in tropical waters when, after volcanos sink, coral growth results in reefs as evidenced by the Cook Islands. Coral reefs can develop into islands over a submerged extinct volcano following uplift as in Makatea and Rennell Island in the Solomon Archipelago which have steep coral cliffs over 100 metres high.

The collision of two plates, resulting in subduction, have contributed to the emergence of the western Pacific arcs of volcanic islands. A new crust has emerged as the East Pacific Rise. In the northeastern Pacific margin there is a lateral shift, through the San Andreas Fault system, of the North American Plate and the Pacific Plate.

Plate movements have also caused fragments of continental crust to be rotated away from landmasses so as to form islands. Zealandia which broke off from Gondwana 70 million years ago with the spreading of the Tasman Sea, has since resulted in island protrusions such as New Zealand and New Caledonia. Related causes of island formation include obduction and subduction at convergent plate boundaries. Malaita and Ulawa in the Solomon Islands are the result of obduction while the effects of subduction can be seen in the formation of volcanic island arcs such as the Aleutian Arc off Alaska and the Kermadec-Tonga Subduction Zone north of New Zealand.

As a result of the collision of the Nazca Plate and the South American Plate, the Andes Mountains emerged in western South America, close to the Peru-Chile Trench. Many large fracture zones aligned in an east-west direction, occur in the floor of the northeastern Pacific.