The Samoa hotspot is a volcanic hotspot located in the south Pacific Ocean. In geology the Hotspot model describes a hot upwelling plume of molten magma through the Earth's crust as an explanation of how volcanic islands are formed. The hotspot idea came from J. Tuzo Wilson in 1963 based on the Hawai'i volcanic island chain.
In theory, the Samoa hotspot is based on the Pacific Tectonic Plate traveling over a fixed hotspot located deep underneath the Samoa islands.[1] The Samoa hotspot includes the Samoan Islands (American Samoa and Samoa), and extends to the islands of Uvea or Wallis Island (Wallis and Futuna) and Niulakita (Tuvalu).[2]
As the Pacific Plate moves slowly over the hotspot, thermal activity builds up and is released in magma plume spewing through the Earth's crust, forming each island in a chain. The Samoa islands generally lie in a straight line, east to west, in the same direction of the tectonic plate 'drifting' over the hotspot.[3]
A characteristic of a 'classic' hotspot, like the Hawaii hotspot, results in islands located further from the hotspot being progressively older with newer and younger islands closest to the fixed hotspot, like the Loihi Seamount, the only submarine volcano which has been studied in detail by scientists. The scientific research from Loihi has resulted in a 'Hawai'i' model for hotspots primarily limited to the information gathered from the Hawai'i islands.[4]
However, the Samoa hotspot is currently an enigma for scientists.[5] In the Samoa Islands, the eastern most island of Ta'u and the western most island of Savai'i have both erupted in the past 150 years. The most recent eruption on Sava'i occurred with Mount Matavanu (1905–1911) and on Ta'u in 1866.[6]
In 1975, geophysicist Rockne Johnson discovered the Vailulu'u Seamount, 45km east of Ta'u island in American Samoa which has since been studied by an international team of scientists. Growing inside the summit crater of Vailulu'u is an active underwater volcanic cone called Nafanua,[5] named after a war goddess in Samoan mythology. The study of Vailulu'u provides scientists with another possible model for hotspots[4] as an alternative to the Hawai'i hotspot model.
An important difference between Vailulu'u and Loihi in Hawai'i, is a total lack of tholeiitic basalt compositions at Vailulu'u[4] although both are located at the eastern most point of their respective island chains. It must be stated that the hotspot is special in many ways. The northern Tonga Islands (Vava'u and Niuatoputapu) are moving away from the Australian plate (Fiji) at rates of c. 130 mm/yr and c. 160 mm/yr, respectively, while the Pacific plate (Niue and Rarotonga) is approaching the Australian plate at c. 80 mm/yr. This implies that Pacific plate is tearing at the corner of the trench-transform boundary at a rate that is the sum of these two (160 + 80) c. 240 mm/yr.[7]