The idea of hotspots was established in 1963 from observations concerning the geology of the Hawaiian Islands. It was well known that the Islands grow progressively older in a line that begins at the southeastern most island of Hawaii and runs northwestward . Mantle plumes are long slender columns of molten or hot rock that originate deep inside Earth's mantle and rise slowly toward the surface, lifting the crust and forming volcanoes. They are thought of as having diameters of 100-200 km and rising rates of perhaps 2 m per year, originated at depths between 700 km and the core mantle boundary (2900 km). Their position appears to be relatively stationary, so the lithospheric plates drift over them. The plumes are therefore independent of the major tectonic elements of the crust and they rise up under continents and ocean plates alike. They have a variety of shapes and sizes, and they originate at various depths. They may consist of hot mantle material rising as blobs rather than in a continuous column. Melting of occurs as the pressure drops when the material rises to the surface.
The plumes may form over regions of locally high concentrations of radioactive elements in the mantle (heat producing) or rise over anomalies in the outer core. They are long lived sources of magma in the mantle which can serve to mark the passage of an overlying lithospheric plate. Mantle plumes appear to be temporary features that form and ultimately fade and die with a typical life span on the order of 100 million years. Bathymetric data in the Pacific Ocean show an L-shaped chain of volcanic islands and submerged volcanoes (the Emperor-Hawaiian chain) that show a progression of ages when dated radiometrically. Dates run from 75 million years at the northwestern end of the chain to 40 million years at the bend, and still active volcanoes in Hawaii . From the distance and orientation, the direction of plate movement and rate can be determined. Hot spots occur under continents as well as beneath ocean basins. They are more easily detected in the oceans, perhaps because the magmas can more readily work their way up through the thinner oceanic lithosphere. The use of hot spots to mark plate motion depends upon a presumption that movement of the hot spots is slight. Other lines of study of plate motion and position of hot spots indicates that the hot spots do move, but this movement is very slow in relation to the movement of plates.
A high concentration of hot spots is found in the African plate . Africa has apparently come to rest over a concentration of hot spots. This has developed uplift and a unique topography. Other plates (Antarctica, China, southeast Asia) which are moving slowly, have higher numbers of hot spots. In rapidly moving plates such as the North and South American plates, hot spots are rare.
Hot spots not only mark the movement of plates, but they also play a part in the movement of plates. When a continent comes to rest, the dome that swells up over a hot spot is subject to fracturing and producing a three armed rift. These may initiate a zone of divergence and to guide the fracturing, although they are not necessarily the only cause. Typically, two arms of the rift open to form an ocean basin and the third arm fails and remains as a fissure in the continental landmass. By restoring the margins of the Atlantic Ocean to their Pangaea position, an abundance of three-armed rifts is revealed. The successful arms merged to form the mid ocean spreading zone and the unsuccessful ones remained as rifts extending into the continents.