Fixed hotspots gone with the wind

Article Abstract:

Volcanic hotspots were thought to be fixed points thjat could be used as reference frames for tectonic plates, but they have proved to be more mobile than expected. Seismic tomography results have shown that volcanic plumes cannot rise through immobile groundwork. Steinberger and O'Connell have assessed Haiwaiian hotspots. Tarduno and Cottrell have shown that research into magnetization of volcanic material is one way to assess hotspot migration and separate it from plate drift.

Natural history, Hawaii, Volcanological research

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Preserving a sense of direction

Article Abstract:

True polar wander (TPW) or the movement of the Earth's rotation axis relative to the mantle has probably been restricted by the lower mantle's rheological nature. Some geophysicists have theorized that plate tectonics, glaciation, geomagnetism and other forces caused TPW to happen often. However, Giorgio Spada and colleagues devised a new geophysical model which shows that the mantle's viscosity has been too irregular to allow much rapid TPW during the last 50 million years.

Polar wandering

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A natural mineral filter

Article Abstract:

Geophysical models indicate that convection can cause compositional layers to form in the Earth's mantle. Furthermore, S. Weinstein's numerical models show that the seismic discontinuity 660 kilometers down functions as a chemical filter that separates buoyant rock from dense rock. Hence the seismic discontinuity, defined as a region where density goes up by 10% in a space of a few kilometers, generates a phase change that in turn gives rise to layers.

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