In geology, hotspots (or hot spots) are volcanic locales thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Examples include the Hawaii, Iceland, and Yellowstone hotspots. A hotspot's position on the Earth's surface is independent of tectonic plate boundaries, and so hotspots may create a chain of volcanoes as the plates move above them. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The alternative plate theory is that the mantle source beneath a hotspot is not anomalously hot, rather the crust above is unusually weak or thin, so that lithospheric extension permits the passive rising of melt from shallow depths. Origin The origins of the concept of hotspots lie in the work of J. Tuzo Wilson, who postulated in 1963 that the formation of the Hawaiian Islands resulted from the slow movement of a tectonic plate across a hot region beneath the surface. It was later postulated that hotspots are fed by narrow streams of hot mantle rising from the Earth's core–mantle boundary in a structure called a mantle plume. Whether or not such mantle plumes exist is the subject of a major controversy in Earth science. At any place where volcanism is not linked to a constructive or destructive plate margin, the concept of a hotspot has been used to explain its origin. In a review article by Courtillot et al. listing possible hotspots, distinction is made between primary hotspots coming from deep within the mantle (possibly originating from the core/mantle boundary), creating large volcanic provinces with linear tracks (Easter Island, Iceland, Hawaii, Afar, Louisville, Reunion, Tristan confirmed, Galapagos, Kerguelen and Marquersas likely) and secondary hotspots derived from mantle plumes (Samoa, Tahiti, Cook, Pitcairn, Caroline, MacDonald confirmed, up to about 20 possible) at the upper/lower mantle boundary that do not form large volcanic provinces but form island chains. Other potential hotspots are the result of shallow mantle material surfacing in areas of lithospheric break-up caused by tension (and are thus a very different type of volcanism). Estimates for the number of hotspots postulated to be fed by mantle plumes have ranged from about 20 to several thousand, with most geologists considering a few tens to exist. Hawaii, Réunion, Yellowstone, Galápagos, and Iceland are some of the most active volcanic regions to which