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In geology, a hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time. J. Tuzo Wilson came up with the idea in 1963 that volcanic chains like the Hawaiian Islands result from the slow movement of a tectonic plate across a "fixed" hot spot deep beneath the surface of the planet. Hotspots are thought to be caused by a narrow stream of hot mantle convecting up from the mantle-core boundary called a mantle plume [1], although some geologists prefer upper-mantle convection as a cause [2] [3] [4]. This in turn has re-raised the antipodal pair impact hypothesis, the idea that pairs of opposite hot spots may result from the impact of a large meteor. [5] Geologists have identified some 40-50 such hotspots around the globe, with Hawaii, Réunion, Yellowstone, Galápagos, and Iceland overlying the most currently active.

Most hotspot volcanoes are basaltic because they erupt through oceanic lithosphere (e.g., Hawaii, Tahiti). As a result, they are less explosive than subduction zone volcanoes, which have high water contents. Where hotspots occur under continental crust, basaltic magma is trapped in the less dense continental crust, which is heated and melts to form rhyolites. These rhyolites can be quite hot and form violent eruptions, despite their low water content. For example, the Yellowstone Caldera was formed by some of the most powerful volcanic explosions in geologic history.

Following the trail of a Hot Spot

As the continents and seafloor drift across the mantle plume, "hot spot" volcanos generally leave unmistakeable evidence of their passage through seafloor or continental crust. In the case of the Hawaiian hot spot, the islands themselves are the remnant evidence of the movement of the seafloor over the hot spot in the Earth's mantle. The Yellowstone hot spot emerged in the Columbia Plateau of the US Pacific Northwest. The Deccan Traps of India are the result of the emergence of the hotspot currently under Réunion Island, off the coast of eastern Africa.

Geologists use hot spots to help track the movement of the Earth's plates. Such hot spots are so active that they often record step-by-step changes in the direction of the Earth's magnetic poles. Thanks to lava flows due to a series of eruptions in the Columbia Plateau, scientists now know that the reversal of magnetic poles takes about 5000 years, fading until there is no detectable magnetism, then reforming in the near-opposite direction.

Hot spots versus island arcs

Hot spot volcanoes should not be confused with island arc volcanoes. While each will appear as a string of volcanic islands. Island arcs are formed by subducting, converging tectonic plates. When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench. This plate melts and becomes new molten material that fuels a chain of volcanoes, such as the Aleutian Islands near Alaska.

List of hotspots

Distribution of selected hotspots. The numbers in the figure are related to the listed hotspots on the left.

External links

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