The great slabs of the crust cover the whole Earth. So when a slab moves, it pulls away from one of its neighbours, letting molten rock flow up to the surface as volcanoes. It also pushes against another neighbour, folding the crust into mountains and causing earthquakes, volcanoes and tsunami. At the same time, it scrapes past its remaining two neighbours, producing more earthquakes. This is why people living near the edges of plates are in more danger than us.
