why do plates move?

• convection currents do not move tectonic plates
• some plates are too wide to be moved by conection currents
• multiple currents move beneath plates and some flow in opposite directions, this would make plates move very slowly and most plates move faster
• the asthenosphere is weak so its convections would not be strong enough to moves the heavy plates
• ridge push and slab pull are the two forces that are believed to move plates
• in ridge push the lithosphere is thinner due to tension, lower pressure so mantle upwells and creates a ridge, the ridge is pushed down and away by gravity. the new lithosphere is also denser so there is additional force away from the ridge
• slab pull occurs at subduction zone, the cold dense ocean lithosphere, which is denser than the asthenosphere beneath, sinks downwards at ocean trenches because it has negative bouyancy and pulls the rest of the plate with it
• slab pull is thought to be the main mechanism, the plates with more margins subducted are the plates moving fastest
• the asthenosphere is ductile, that allows the lithosphere to move past and above it, this allows the plates to move