Summary of volcanism of Samoa
Aleni Fepuleai
Time: 11-12 noon
Venue: M107 Lecture Theatre, Marine Campus
Geochemical analyses of lavas from the deep submarine and subaerial volcanoes of the Samoan island chain reveal a combination of ‘shield volcanism’ and ‘rejuvenated volcanism’. The shield volcanism is thought to represent an earlier phase of activity associated with a hot spot-driven mantle plume. The present location of the hotspot lies at the eastern end of the chain in American Samoa at the active underwater volcano of Vailulu’u. The phase of rejuvenated volcanism took place after a long period of dormancy and erosion.
Volcanic activity in Samoa is intimately associated with the interaction of two major tectonic plates, the Pacific Plate and the Australian Plate. The westward movement of the Pacific plate at this point would be expected to carry the products of volcanic activity in the same direction. We should therefore anticipate a systematic increase in the age of the volcanic islands that lie to the west of the Vailulu’u hot spot. This is exactly what is seen along the Hawaiian island chain, for example. Yet in Samoa, the age of the islands appears to become younger towards both ends of the chain. At the western end, Matavanu, to the northeast of Savai’i, last erupted in 1911, while at the eastern end lies the active underwater volcano of Vailulu’u. This conundrum has led to decades of debate about the origins of Samoan volcanism.
