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Latitude and parallels

One of the important modifications of basic plate tectonic theory is the concept of the hot spot. These are locations where a fairly narrow plume of magma is rising from the asthenosphere to the surface, producing volcanoes. Many hot spots apparently develop from mantle plumes that originate deep within the mantle.

Hot spots may occur well away from plate boundaries, often in the middle of a plate. It is not yet completely understood why these hot spots occur where they do, but the existence of hot spots has been helpful in verifying plate motion.

Evidently, hot spots can remain active in the same location for millions of years. While the hot spot remains in the same place, the plate above continues to move above it. Currently active volcanoes are found directly over the hot spot, while the moving plate carries older volcanoes off the plume, at which time they become inactive. Ongoing plate motion carries these old volcanoes farther and farther away from the hot spot, resulting in a chain of extinct volcanoes.

The Hawaiian Islands are the best-known example of an island chain produced by a hot spot. The only currently active volcanoes are found on the island of Hawaii in the southeast part of the island chain. It is believed that this island is currently over the hot spot.

The map below shows the ages of volcanic rocks in the Hawaiian chain. Notice that the ages (in millions of years) of the volcanic rocks becomes progressively older as we follow the islands to the northwest. The pattern of islands in the Hawaiian chain shows the general direction of movement of the Pacific Plate, and from the ages of the rocks, we can infer the rate of plate movement.