Hot mantle rock that rises toward the earth's surface in a narrow column is called a
mantle plume. Plumes can be located beneath continental or oceanic crust or along plate boundaries. Plumes are thought to spread out laterally at the base of a continent, creating increased pressure that stretches the crust and results in uplift, fracturing, rifting, or flood basalts. Mantle plumes are thought to be strong enough to induce rifting and the formation of plates. The pressure creates a domed region that eventually splits in a three‐pronged pattern (triple junction or
triple point). If rifting continues, two of the three faults become active, forming the continental margins of two new continents. The two faults join to form an active divergent boundary that dissipates the tectonic forces. The third “arm” becomes a
failed rift, or
aulacogen, that rapidly fills with sediment.
The best example of a triple junction in the world is provided by the three faults marked by the Red Sea, the Gulf of Aden, and the inactive African Rift Valley. The rifting is separating the Arabian Peninsula from the African continent and is thought to be related to a mantle plume. Other areas that are underlain by mantle plumes are the Hawaiian Islands (oceanic crust) and Yellowstone National Park (continental crust) in the United States.