A "hotspot" is an area in the Earth’s mantle from which hot plumes rise upward, forming volcanoes on the overlying crust.

The best example of a hotspot producing a line of volcanic islands is the Hawaiian hot spot. This drawing, from Thurman’s Introduction to Oceanography, illustrates how the Hawaiian chain formed as the Pacific tectonic plate moved over the hot spot.

The best example of a hotspot producing a line of volcanic islands is the Hawaiian hotspot. This drawing, from Thurman’s Introduction to Oceanography, illustrates how the Hawaiian chain formed as the Pacific tectonic plate moved over the hotspot.

A hotspot is theorized to form as one of Earth's outer tectonic plates moves over an unusually hot part of the Earth's mantle and large amounts of magma rise up, piercing through the plates and producing large volcanic eruptions at the Earth’s surface. Hotspot volcanism would thus be unique because it does not occur at the boundaries of Earth’s tectonic plates, where other volcanism occurs.

The mantle plumes that form hotspots are thought to be relatively stationary, while tectonic plates are not. As the plates continue to move away from oceanic volcanoes, the volcanoes cool and subside, producing older islands, atolls, and seamounts. As continental volcanoes move away from a hotspot, they cool, subside, and become extinct. In this way, hotspots can produce lines of volcanoes, known as hotspot tracks.

A seamount might stay volcanically active for two or three million years while it is above a hotspot: lava streams out of its summit and down its flanks, building up a volcanic mountain. As the volcano is carried away by the moving tectonic plate, its volcanic activity begins to wane and eventually goes quiet, only to be replaced by volcanic activity at a new seamount being born on the ocean floor that has moved on top of the hotspot.

This is occurring today in Hawaii, perhaps the most well-known example of a hotspot track. Here, volcanic activity on the Island of Hawaii is slowly being replaced by activity on nearby Loihi seamount. The Hawaiian hotspot is believed to have been active at least 70 million years, producing a volcanic chain that extends 6,000 kilometers (3,750 miles) across the northwest Pacific Ocean.

Keep in mind that much of what we think we know about hotspots is based on theories. There continues to be scientific debate about whether hotspots are actually deep phenomena or even “fixed” in position. Such is the nature of science and why we continue to explore and learn.

 

For More Information:

What Is A Hotspot?, GalAPAGoS: Where Ridge Meets Hotspot

Geological Origin of the New England Seamount Chain, Mountains in the Sea 2003

Volcanic History of Seamounts in the Gulf of Alaska, Exploring Alaska’s Seamounts 2002

 

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