Hot Spots

Abstract

AbstractAlthough the vast majority of volcanoes on Earth are related to plate boundaries-mid-ocean ridges and subduction zones, approximately 5% are classified as “hot spots”. Hot spots are the product of mantle diapirs (diapeírein, Greek to perforate) or plumes (because of their shape) that rise through the mantle as finger-shaped hot currents and penetrate the crust. In spite of their relatively low numbers, they play an important role in the convection system of the Earth’s mantle and are responsible for about 5–10% of the melts and energy emitted by the Earth. At present, approximately fifty hot spots have been identified in both continents and oceans (Fig. 6.1). Although most are located in the interior of plates (“intraplate volcanism”, e. g., Hawaii), some hot spots are either coincident with mid-ocean ridges (e. g., Iceland) or in close proximity (e. g., Azores, Tristan da Cunha). Mantle plumes and the resulting hot spots are responsible for the formation of large volcanic complexes; these include volcanic chains up to several thousand kilometers long and huge flood extrusions, commonly called large igneous provinces or LIP, that consist of basaltic lavas. Plumes are produced in the lowermost mantle adjacent to the core within the so-called D″ layer (see below; Fig. 6.2), at a depth of about 2900 km. The hot source in the mantle is generally considered to be fixed in its position over long periods of time. The existence of hot spots and their significance as fixed points was first established by J. Tuzo Wilson, one of the doyens of plate tectonics (Wilson 1963).