What is a hotspot and how do you know it's there?

Most volcanic eruptions occur near the boundaries of tectonic plates, but there are some exceptions. In the interior of some tectonic plates, magma has been erupting from a relatively fixed spot below the plate for millions of years. As the plate continuously moves across that spot, a trail of progressively older volcanic deposits is left at the surface. The Hawaiian Islands are a good example of this. The island of Hawai‘i currently sits above the active hotspot, while a chain of older (and no longer active) island volcanoes extend to the northwest, in the direction of plate movement. A few hotspots (like the one in Iceland) have also been found at diverging plate boundaries.

Scientists don’t fully understand how and why hotspots occur, and there is vigorous scientific debate about their origins. A frequently-used hypothesis suggests that hotspots form over exceptionally hot regions in the mantle, which is the hot, flowing layer of the Earth beneath the crust. Mantle rock in those extra-hot regions is more buoyant than the surrounding rocks, so it rises through the mantle and crust to erupt at the surface.

Hotspots and their trails on the earth’s surface do not develop suddenly (within the span of a human lifetime, for example). Scientists are only able to identify hotspots because of their relatively fixed locations beneath the tectonic plates, which produce tracks of surface volcanism spanning millions of years.

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Date published: March 30, 2006

Volcano Watch — On the Trail of Hotspots: the Galapagos and Hawaiian Islands

The Galapagos Islands are perhaps best known for their unique species of plants and animals and their role in influencing Charles Darwin and others in developing modern theories of evolution.

Date published: April 14, 1995

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Many of the islands that dot the center of the Pacific Ocean are made up of active, dormant, or extinct volcanoes, whose geologic histories are characteristic of "hot spot" volcanism.
 

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Map of Hawaii
November 6, 2018

Hawaiian Islands

Map of the Hawaiian Islands.

Hotspots...
April 10, 2017

Hotspots

This is a map of the earth. The thick dashed line shows the ridge formed by the Hawaiian hot spot during the last 80 million years. The arrows show the direction and rate of motion of selected plates relative to the hot spots. The plate boundaries are shown by the lines of medium weight, and the "Pacific ring of fire" plate boundaries by heavier lines. The dots mark the

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The San Francisco Volcanic Field-Arizona's Hotspot...
February 20, 2017

The San Francisco Volcanic Field-Arizona's Hotspot

SP Crater, in the San Francisco Volcanic Field, is an excellent example of a cinder cone and associated lava flow. This flow extends 4 miles from the cone and is only about 100 feet thick.

Exploring the deep source of Hawaiian volcanoes...
January 9, 2014

Exploring the deep source of Hawaiian volcanoes

Map showing the submarine shape of the Hawaiian hotspot track, which extends from the Hawaiian Islands, through a prominent bend in the middle of the Pacific Ocean, to Alaska's Aleutian Islands. The inset shows the volcanoes in the main Hawaiian Islands. After the formation of O‘ahu, the volcanoes can be categorized as belonging to either the "Loa" (black triangles) or "

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Graphic depicting the path left by the Yellowstone hotspot as the c...
October 3, 2000

Map showing the path of the Yellowstone hotspot.

Yellow and orange ovals show volcanic centers where the hotspot produced one or more caldera eruptions- essentially "ancient Yellowstones"- during the time periods indicated. As North America drifted southwest over the hotspot, the volcanism progressed northeast, beginning in northern Nevada and southeast Oregon 16.5 million years ago and reaching Yellowstone National Park

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Track of Yellowstone hotspot...

Track of Yellowstone hotspot

Shaded relief map showing the path of the Yellowstone hotspot. Yellow and orange ovals outline past caldera eruptions during the time periods indicated (orange calderas are the most recent). The calderas progress from oldest in northern Nevada to youngest in Yellowstone National Park as the North American plate passed over the relatively stationary hotspot. Black lines

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Cross section through the Earth showing the Yellowstone mantle plum...

Cross section through the Earth showing the Yellowstone mantle plume

Depth cross section through the Earth, form the surface to the core-mantle boundary. The location of the section is shown by the purple line on the map. Warm colors indicate slower seismic velocities, which are areas of higher temperature. A plume of hot material originates at the core-mantle boundary and extends upward to the Yellowstone hotspot (marked by the volcano

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