Plumes or not? A hot debate
Gillian R. Foulger
Volcano Hazards Team,
U.S. Geological Survey, Menlo Park
September 19th, 2004
Over the past few years it has become clear that many scientists harbour varying degrees of skepticism in the plume model. This ranges from doubt in the very large numbers of plumes advocated for regions of relatively minor-volume volcanism such as eastern Anatolia, Italy and the Baikal rift, to doubt that the fundamental model is itself physically plausible in a realistic Earth, which behaves quite differently from a laboratory apparatus.
The classical plume hypothesis, originally suggested by Morgan (1971) may be distinguished from the contemporary hypothesis. The former, at one extreme, was clearly defined and made clear predictions. The latter, however, in its extreme form, is sufficiently flexible to account for every observation and its inverse, and therefore cannot be disproved. For this reason, effort in the plume-skeptic community has mainly focused on seeking viable alternative mechanisms for generating melting anomalies rather than attempting to disprove the existence of plumes at particular localities.
Major collective efforts in the last year or so include:
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A Penrose conference Plume IV: Beyond the Plume Hypothesis, held in Hveragerdi, Iceland, September 2003. Over 60 scientists from 12 nations gathered to discuss alternatives that included models based on variations in lithospheric stress coupled with mantle fertility, meteorite impacts, and local, upper-mantle convection cells. Numerous papers were also presented, proposing models for individual hot spots. All the conference resources may be accessed at http://www.mantleplumes.org/Penrose/Info%2BDownloads.html
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The website http://www.mantleplumes.org/ expanded greatly and now contains contributions from over 100 scientists. It comprises over 100 webpages, about half of which are critical scientific essays relating to plume models at particular localities, alternative mechanisms for generating melt, or generic issues such as mantle temperature, composition and the systematics of various isotopes.
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A book, “Plates, Plumes and Paradigms” to be published by the Geological Society of America is nearing completion. Originally inspired by the Plume IV Penrose conference, this book will not comprise conference proceedings but rather a compendium of resources related to hot spots and plumes. It will include approximately 50 scientific articles that take a critical look at plume models, along with hot spot maps, tomographic images and other reference material. Submitted chapters and their status in the review process may be viewed at http://www.mantleplumes.org/TopPages/TheP3Book.html
The next major public discussion forum in this subject will be the special session “Plumes or not?” at the forthcoming Fall Meeting of the American Geophysical Union. This, and all other collective efforts are directed at encouraging discussion, and in this spirit both plume-supportive and plume-skeptical contributions are equally welcome. We hope that more individuals, particularly those interested in defending the plume model, will feel inclined to contribute.
Reference: Morgan, W.J., 1971, Convection plumes in the lower mantle: Nature, v. 230, p. 42-43.