Mantle plumes

Morgan (1971) originally proposed that “plumes”, which he described as hot upwellings of relatively primordial material, rise from the deep mantle and feed surface “hot spots” such as Iceland and Hawaii. Such plumes rise because of thermal buoyancy, and must originate at a thermal boundary layer. The only such layer known to exist in the deep mantle is the core-mantle boundary (D"), and thus “Morgan-type” plumes are generally assumed to rise from this layer.

This theory has been popular for over 30 years. However, irrefutable evidence for such plumes has still not been confirmed, and contrary, or unexpected observations are often reported. On the other hand, low-wave-speed seismic anomalies with different shapes, e.g., shallow, or very wide bodies have been found. Such observations led to diversification of the range of features that scientists call “plumes”. A clear, widely accepted definition of a plume thus does not currently exist, and the word “plume” is often used by different scientists to mean different things. Furthermore, it has become essentially impossible to disprove the plume hypothesis because the term “plume” has become vague and all-embracing.

Very recently, a vigorous global debate has developed concerning whether plumes exist at all. For more information on this exciting new aspect of Earth Science, visit http://www.mantleplumes.org/