Hi All. I sent a copy of the post by David Thomson concerning the movement of the Pacific Plate to Lowell Whiteside. Here is his reply. Take Care…Don in creepy town

Thanks Don,
I do not have access to earthwaves here, but you can post this reply if you wish.

The idea that large scale convection cells exist in the mantle is as outdated as the idea that the earth is flat. Tomographic imaging of the earth's interior has shown that convection cells tend to be relatively small and are generally concentrated in regions near mid ocean-ridges. For many years now it has been acknowledged that there are a number of forces acting on the surface of the earth which causes differential motion on the
surface plate.

Gravity is the most important mover and shaker on the earth. Plates subduct because heavier ocean floor material encounters lighter continental material, which is something like foam floating on a sea of heavier matter. Plates are pushed into subduction zones by the force exerted by the topography of mid-ocean ridges - called ridge push. Once subduction begins, the heavier plate pulls the rest of the plate with it as it moves into the interior of the earth. This is called plate pull. Several other forces are also occurring.

There is a drag force under the plates as they move over the mantle and there is a restraining force due to friction at the interface between the subducting ocean and continental plate. These, however, have been shown to very small compared with the force exerted simply by the higher density of the subducting plate with respect to the hotter material around it and the push from the high mountain ridges in the mid-ocean ridge areas. In fact, many consider convection to be caused by plate subduction rather than the cause of plate subduction.

The ideas of global convection cells simply do not match the observations which have been made over the past 25 years. New hypothesis and theories have arisen which have modified these simplistic ideas more realistically match the current observations.

That is the way science work. As far as I know there are no "undisputed fact", even the theory of gravity is subject to change, and complicated systems like earth science are continuously in a state of intellectual flux.