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Hotspot (geology)

Volcanic region hotter than the surrounding mantle

  • 10 min read
  • 5 chapters
A diagram showing the Hawaii hotspot and the inferred underlying mantle plume in cross-section.
Joel E. Robinson, USGS. · Public domain

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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 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 has been the subject of a major controversy in Earth science, but seismic images consistent with evolving theory now exist.

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. A review article by Courtillot et al. listing possible hotspots makes a distinction between primary hotspots coming from deep within the mantle and secondary hotspots derived from mantle plumes. The primary hotspots originate from the core/mantle boundary and create large volcanic provinces with linear tracks (Easter Island, Iceland, Hawaii, Afar, Louisville, Reunion, and Tristan confirmed; Galapagos, Kerguelen and Marquersas likely). The secondary hotspots originate at the upper/lower mantle boundary, and do not form large volcanic provinces, but island chains (Samoa, Tahiti, Cook, Pitcairn, Caroline, MacDonald confirmed, with up to 20 or so more possible). 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 dozen to exist. Hawaii, Réunion, Yellowstone, Galápagos, and Iceland are some of the most active volcanic regions to which the hypothesis is applied. The plumes imaged to date vary widely in width and other characteristics, and are tilted, being not the simple, relatively narrow and purely thermal plumes many expected. Only one, Yellowstone, has as yet been consistently modelled and imaged from deep mantle to surface.

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