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USGS CMG InfoBank: Push and Pull of Plates

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Comment: 16:10 - 17:34 (01:24)
Source: Annenberg/CPB Resources - Earth Revealed - 6. Plate Dynamics
Keywords: "Gary Ernst", lithosphere, "plate tectonics", trench, "mid-oceanic ridge", modeling, asthenosphere, plate

Our transcription: There are those who believe that because the lithospheric plates where they descend in the trenches are of greater density than the material they displace, that, in fact, like the covers falling off the edge of the bed, they are being pulled down.
So plate push at the ridge because of hot rising material sliding off the ridge and trench pull are all aspects of the process.
What we know for certain is that the lithospheric motions are as described in all those models, but none of them is a paramount argument or model for explaining the process of actual plate motivation, why plates move.
I personally believe that because the plates that have trenches, that are moving down trenches, are going fairly fast, 10 - 12 centimeters a year; whereas, those that are simply moving away from ridges that are not tied or hooked to descending limbs are only going a few centimeters a year, that, in fact, there is an important trench pull.
But, I believe it's also possible there is a small at least plume drive or rising asthenosphere column which causes the plates to move away from the ridge crests as well.

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