Hot Spots and Mantle Plumes

Hot spots are anomalous areas of surface volcanism that cannot be directly associated with plate tectonic processes. The term hot spot is used rather loosely. It is often applied to any long-lived volcanic center that is not part of the global network of mid-ocean ridges and island arcs. The classic example is Hawaii. Anomalous regions of thick crust on ocean ridges are also considered to be hot spots. The prototype example is Iceland. There is little agreement on the total number of hot spots. Several hot spot lists have been published, and the number of volcanic centers included on these lists ranges from about 20 to more than 100. In one of his original papers associating hot spots with mantle plumes, Morgan (1972) listed 19 hot spots. Crough and Jurdy (1980) listed 42, Wilson (1973) listed 66, and Vogt (1981) listed 117. Table 11.1 gives the coordinates of 30 hot spots from the list of Crough and Jurdy (1980), and Figure 11.1 shows the locations of 20 prominent hot spots (see also Figure 2.23). In many cases hot spots have well-defined tracks associated with volcanic ridges or lines of volcanic edifices; these are also shown in Figure 11.1 and in Figure 2.23. A few hot spots and the tracks they have made appear on all lists, either because of high eruption rates in the recent past or because they have produced conspicuous traces. Among these are Hawaii, Iceland, Reunion, Cape Verde, and the Azores. Others, such as Bermuda, do not have an extensive volcanic history, but qualify as hot spots because they sit atop broad topographic rises or seafloor swells. Large continental volcanic centers, such as Yellowstone and some in East Africa, make most lists because of their similarity to oceanic hot spots. The concept of stationary heat sources in the mantle was introduced by Wilson (1963c) as an explanation for the Hawaiian chain. Morgan (1971, 1972) was the first to advocate a global array of deep mantle plumes for the origin of hot spots. Morgan envisioned mantle plumes to be vertical conduits in which hot mantle material rises buoyantly from the lower mantle to the lithosphere at velocities as large as 1myr−1. The plume concept has steadily gained acceptance in spite of the fact that the geological, geophysical, and geochemical evidence for plumes, while growing, is still largely indirect. There are also some critical observations that plume theory has never satisfactorily explained.