How earths crust move?

Answer 1

Earth's crust and the solid rocky and brittle upper mantle are known as the lithosphere. This is broken up into a number of different sections or pieces known as tectonic plates.

Underlying the lithosphere is the asthenosphere made up of the softer mantle rocks that behave as a viscous fluid (like an extremely thick treacle).

Heat within the earth causes the asthenosphere to convect. This movement causes the overlying lithosphere to move as well.

Also where mantle material rises to shallower depths it undergoes a process known as decompression melting. This causes the formation of magma which rises to Earth's surface. This hot (and therefore lower density) material forms a raised area in the Earth's crust known as a mid-ocean-ridge. Gravity acts to try and pull the buoyant hot new crust back down and this force is transferred horizontally through the crust in a process known as "Ridge Push". As the material cools and travels away from the mid-ocean -ridge it sinks slightly back down due to it's increased density and so lower buoyancy.

Ultimately this dense oceanic crust may meet a tectonic plate composed of continental crust which has a lower density and is more buoyant than the oceanic crust. Because of this the denser oceanic crust is forced down below the continental crust. This process is known as subduction. The force of gravity acting on the subducting slab is transferred into the rest of the slab acting to pull it towards the subduction zone. This process is known as "slab pull".

Answer 2

and also sea floor spreading affects that we so called volcanic eruption. thanks i hope i can help!