These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes, such as the 1906 one that devastated San Francisco. 4:46 ...

They found that a divergent plate boundary, where two plates move apart, was forcefully and rapidly turned into a convergent boundary where one plate eventually began subducting.

The estimate is 50% of plate tectonic movement is driven by this heat, and about 20 terawatts of heat flows between the core and the mantle. That's just slightly more than the average total power ...