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The most heavily challenged element of Wilson's theory is whether or not hotspots are indeed fixed relative to the overlying tectonic plates.Drill samples, collected by scientists as far back as 1963, suggest that the hotspot may have drifted over time, at the relatively rapid pace of about 4 centimeters (1.6 in) per year during the late Cretaceous and early Paleogene eras (81-47 Mya); In 1987, a study published by Peter Molnar and Joann Stock found that the hotspot does move relative to the Atlantic Ocean; however, they interpreted this as the result of the relative motions of the North American and Pacific plates rather than that of the hotspot itself.This cycle of growth and dormancy strings together volcanoes over millions of years, leaving a trail of volcanic islands and seamounts across the ocean floor.According to Wilson's theory, the Hawaiian volcanoes should be progressively older and increasingly eroded the further they are from the hotspot, and this is easily observable; the oldest rock in the main Hawaiian islands, that of Kaua Another consequence of his theory is that the chain's length and orientation serves to record the direction and speed of the Pacific Plate's movement.
These melting anomalies are normally called "hotspots", but under the shallow-source hypothesis the mantle underlying them is not anomalously hot.
A mantle plume would initiate at the interface when the warmer lower layer heats a portion of the cooler upper layer.
This heated, buoyant, and less-viscous portion of the upper layer would become less dense due to thermal expansion, and rise towards the surface as a Rayleigh-Taylor instability.
This "mid-plate" volcanism builds peaks that rise from relatively featureless sea floor, initially as seamounts and later as fully-fledged volcanic islands.
The local tectonic plate (in the case of the Hawaii hotspot, the Pacific Plate) slowly slides over the hotspot, carrying its volcanoes with it without affecting the plume.