Mechanisms of Plate Motion Chapter 9.5 Mechanisms of Plate Motion

Causes of Plate Motion Plate move because of convection occurring in the mantle. During convection warm, less dense material rises, and cooler, more dense material sinks. This is called convective flow.

Slab-Pull and Ridge-Push Slab-pull – this is where old oceanic crust, which is cool and dense, sinks into the asthenosphere and “pulls” trailing lithosphere along. This is the primary downward arm of convective flow in the mantle. Ridge-push is where oceanic lithosphere slides down the sides of the oceanic ridge. This causes spreading between plates.

Mantle Convection Mantle plumes are the upward flowing arms in mantle convection. This can be hot spots or volcanoes. Whole mantle convection is where slabs of cold oceanic lithosphere descend into the lower mantle and hot mantle plumes move heat toward the surface. This process moves plates around the Earth.