eventually,one plate will give way and slip under the other plate. this sudden movement, sometimes only one meter, has tremendous consequences. in the pacific ocean and hit indonesia, thailand, and sri lanka,killing 230,000 people, is an example of continental drift and plate tectonics. the eruption of volcanoes is one factor in changing the earth is crust. when two tectonic plates move away from each other, magma flows up from the mantle, filling the space between the two plates. this is how volcanoes are created (many of them underwater)