Volcanic region hotter than the surrounding mantle
Diagram showing across section through Earth at the Hawaii hotspot.Magma originating in themantle rises into theasthenosphere andlithosphere. A chain of volcanoes is created as the lithosphere moves over the source of magma. ("Ma" means millions of years old/ago).
Ingeology,hotspots (orhot spots) arevolcanic locales thought to be fed by underlyingmantle that is anomalously hot compared with the surrounding mantle.[1] Examples include theHawaii,Iceland, andYellowstone hotspots. A hotspot's position on the Earth's surface is independent oftectonic plate boundaries, and so hotspots may create a chain of volcanoes as the plates move above them.
There are twohypotheses that attempt to explain their origins. One suggests that hotspots are due tomantle plumes that rise as thermaldiapirs from the core–mantle boundary.[2] The alternativeplate 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.[3][4]
Schematic diagram showing the physical processes inside the Earth that lead to the generation of magma. Partial melting begins above the fusion point.Map showing approximate location of many current hotspots and the relationship to current tectonic plates and their boundaries and movement vectors
The origins of the concept of hotspots lie in the work ofJ. Tuzo Wilson, who postulated in 1963 that the formation of theHawaiian Islands resulted from the slow movement of atectonic plate across a hot region beneath the surface.[5] It was later postulated that hotspots are fed by streams of hotmantle rising from the Earth'score–mantle boundary in a structure called amantle plume.[6] Whether or not such mantle plumes exist has been the subject of a major controversy in Earth science,[4][7] but seismic images consistent with evolving theory now exist.[8]
At any place wherevolcanism 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.[9] 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.[8]Hawaii,Réunion,Yellowstone,Galápagos, andIceland 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.[8] Only one, Yellowstone, has as yet been consistently modelled and imaged from deep mantle to surface.[8]
Most hotspot volcanoes arebasaltic (e.g.,Hawaii,Tahiti). As a result, they are less explosive thansubduction zone volcanoes, in which water is trapped under the overriding plate. Where hotspots occur incontinental regions,basalticmagma rises through the continental crust, which melts to formrhyolites. Theserhyolites can form violent eruptions.[10][11] For example, theYellowstone Caldera was formed by some of the most powerful volcanic explosions in geologic history. However, when the rhyolite is completely erupted, it may be followed by eruptions of basaltic magma rising through the same lithospheric fissures (cracks in the lithosphere). An example of this activity is theIlgachuz Range in British Columbia, which was created by an early complex series oftrachyte andrhyolite eruptions, and late extrusion of a sequence of basaltic lava flows.[12]
The hotspot hypothesis is now closely linked to themantle plume hypothesis.[13][8] The detailed compositional studies now possible on hotspot basalts have allowed linkage of samples over the wider areas often implicate in the later hypothesis,[14] and its seismic imaging developments.[8]
Hotspot volcanoes are considered to have a fundamentally different origin fromisland arc volcanoes. The latter form oversubduction zones, at converging plate boundaries. When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench. This plate, as it is subducted, releases water into the base of the over-riding plate, and this water mixes with the rock, thus changing its composition causing some rock to melt and rise. It is this that fuels a chain of volcanoes, such as theAleutian Islands, nearAlaska.
The jointmantle plume/hotspot hypothesis originally envisaged the feeder structures to be fixed relative to one another, with the continents andseafloor drifting overhead. The hypothesis thus predicts that time-progressive chains of volcanoes are developed on the surface. Examples includeYellowstone, which lies at the end of a chain of extinct calderas, which become progressively older to the west. Another example is the Hawaiian archipelago, where islands become progressively older and more deeply eroded to the northwest.
Geologists have tried to use hotspot volcanic chains to track the movement of the Earth's tectonic plates. This effort has been vexed by the lack of very long chains, by the fact that many are not time-progressive (e.g. theGalápagos) and by the fact that hotspots do not appear to be fixed relative to one another (e.g.Hawaii andIceland).[15] That mantle plumes are much more complex than originally hypothesised and move independently of each other and plates is now used to explain such observations.[8]
In 2020, Wei et al. usedseismic tomography to detect the oceanic plateau, formed about 100 million years ago by the hypothesized mantle plume head of the Hawaii-Emperor seamount chain, nowsubducted to a depth of 800 km under eastern Siberia.[16]
Distribution of hotspots in the list to the left, with the numbers corresponding to those in the list. The Afar hotspot (29) is misplaced.
Map all coordinates usingOpenStreetMapDownload coordinates asKML
In the following list of hotspots, "az" is theazimuth of the hotspot track; "w" is the "weight", or estimated accuracy, of the azimuth (1 is most accurate, 0.2 is least accurate).[19]
^Donald Hyndman; David Hyndman (1 January 2016). Natural Hazards and Disasters. Cengage Learning. pp. 44–.ISBN978-1-305-88818-0.
^Wolfgang Frisch; Martin Meschede; Ronald C. Blakey (2 November 2010). Plate Tectonics: Continental Drift and Mountain Building. Springer Science & Business Media. pp. 87–.ISBN978-3-540-76504-2.
^O'Connor, J. M.; le Roex, A. P. (1992). "South Atlantic hot spot-plume systems. 1: Distribution of volcanism in time and space".Earth and Planetary Science Letters.113 (3):343–364.Bibcode:1992E&PSL.113..343O.doi:10.1016/0012-821X(92)90138-L.
