Samoan Islands - Geology

Geology

A possible model for the formation of the volcanic Samoa island chain is explained by the Samoa hotspot situated at the east end of the Samoa Islands. In theory, the Samoa hotspot is a result of the Pacific Tectonic Plate moving over a 'fixed' deep and narrow mantle plume spewing up through the Earth's crust. The Samoa islands generally lie in a straight line, east to west, in the same direction the Plate is moving. In the classic hotspot model, primarily based on studies of the Hawaii hotspot, the volcanic islands and seamounts further away from the Samoa hotspot should be progressively older. However, Savai'i, the most western of the Samoa island chain, and Ta'u Island, the most eastern of the Samoa islands, both erupted in the last century, data which is an enigma for scientists. Another discrepancy in the data from the Samoa islands is that subaerial rock samples from Savai'i, the most western of the islands, were too young by several million years to fit the classic hotspot model of age progression in an island chain, raising arguments among scientists that the Samoa islands does not have a plume origin. The nearness of the island chain to the Tonga Trench at the south became a possible explanation for these discrepancies as well as the possibility that the islands were formed by magma seeping through cracks in stressed fracture zones. However, in 2005, an international team gathered further submarine samples from the deep flanks and rifts of Savai'i. Tests on these later samples showed much older ages, about five million years old, that fit the hotspot model.