- Samoan islands originated from hot spot volcanic systems. Eruptive centres are aligned along a rift. Older shield volcanic systems have been reactivated with modern volcanism on Savai’i, Upolu, and Tutuila.
- Savai’i is the largest shield volcano in the South Pacific, with the chain formed in a linear (eastward progression) manner as the Pacific Plate moved across a hot spot.
- Subsequently (millions of years later), volcanism was rejuvenated along a narrow ~200km long rift system. This volcanic rift system has been associated with juxtaposition of hot spot and trench and associated lithospheric cracking due to tectonic stresses from the trench plate flexure deformation. Different theories attribute various sources of the magmatic activity, whether associated with a plume-depleted asthenosphere (viscous “keel”) or a thermally anomalous, upwelling region of the mantle (plume) beneath Samoa.
- Eruptions from 1905-1911 on Savai’i have resulted in extensive lava coverage across the island. There are more than 400# volcanic cones across the island in various stages of erosion. There is a WNW-ESE trending rift zone across the island with a large escarpment in the north and northwest side of the island. There are hot springs on the island. With history of volcanic activity, it is believed that an extensive magma chamber system with significant heat flux likely exists beneath the island.
