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Science Frontiers ONLINE No. 103: Jan-Feb 1996 |
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But what about the hawaiian volcanic chain?
The classical, oft-repeated explanation for the formation of the Hawaiian chain of volcanic islands and submerged sea-mounts -- thousands of kilometers long -- is that the surface lithographic plate has been sliding over a fixed mantle plume. The heat brought to the surface via this plume has created the volcanic chain as the surface plate has drifted over it during the past 73-or-so million years.
Obviously, this model is starkly contradicted by the fossil plume under South America (described above) that seems to have been firmly attached to the South American plate for 120 million years. No differential motion there!
Now, from a different line of evidence, P.D. Ihinger is challenging the well-entrenched "Hawaiian-volcanic-chain" theory. For example, the Hawaiian volcanoes do not line up exactly. There are dozens of short, overlapping segments rather than a continuous trace across the Pacific basin. On the map, you will also see a sharp dog-leg in the trace. Further, the volcanoes Mauna Loa and Mauna Kea, only 40 kilometers apart, disgorge lavas that are distinctly different. Something is not right!
Ihinger postulates a strong mantle current flowing ponderously under the Hawaiian chain, dissecting the rising plume of hot rock into small "plumelets". These discrete blobs of hot rock are dispersed by the current of semi-solid rock and disrupt the expected simple pattern.
(Ihinger, Phillip D.; "Mantle Flow beneath the Pacific Plate: Evidence from Seamount Segments in the Hawaiian-Emperor Chain," American Journal of Science, 295:1035, 1995. Also: Monastersky, R.; "Volcanoes Reveal Earth's Hidden Currents," Science News, 148: 357, 1995)
Comment. Although a bit abstruse, these geological anomalies detected under South America and Hawaii threaten one of the crowning achievements of modern geology and geophysics.