From Sarah Bowes
Caterham, Surrey
Robert Duncan’s study of “moving” volcanic hot spots
(15 December, p 20) was
interesting but flawed. Using only the example of Hawaii’s Big Island, he
suggests that the direction of magnetisation in the Big Island’s lava stack
shows that the underlying hot spot has probably moved relative to the oceanic
crust.
However, the three other main Pacific hot spots—Macdonald, Louisville
and Easter Island—give the lie to his theory. The line of the
Hawaii-Emperor seamount chain is identical to that of the austral Cook
Islands-Marshall Gilbert seamount chain. Both are “kinked” at exactly the same
angle at the same time— 43 million years ago. Elsewhere, the line of the
Louisville Ridge seamounts draws the same parallel to that of the Tuamotu
Archipelago. These hot-spot trails have the same distinctive kink, also aged 43
million years. Sampling of the seamounts has proved the ages of the respective
chains, and the age of the “elbow bend” in all.
It seems unlikely that all four hot spots are moving in the same direction
through the Earth’s mantle. It is more likely that they are indeed stationary,
that the Pacific plate did change direction 43 million years ago, and that the
magnetic anomalies noted by Robert Duncan were caused by local disturbance of
the Earth’s magnetic field during intense phases of volcanic activity. The
active Krakatoa, for example, is notorious for disturbing ships’ navigation
systems.
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