When two continents collide after the entire ocean floor which separated them has been subducted, their deformed leading edges meet and one of the continents will begin to slide underneath the other, leading to a thickened lithosphere. This process is called underplating. The resultant collision creates a giant internal mountain range whose position marks the seam along which the original continental masses have been joined. Because these mountains represent the compressed welded edges of continents, the lithosphere is thickened, preventing magma from rising to the surface; as a consequence, such a boundary only rarely exhibits volcanism. However, the forces which deform these continents create enormous stresses which are released as earthquakes. Because these events involve non-subducting lithosphere, they are of the shallow and intermediate focus type. The Himalayas mark such a plate junction which is still active, where India is underplating Asia. The Urals delineate where Asia and Europe collided, and the Appalachians mark the edge of a large supercontinent which was originally formed by the collision between Eurasia and North America, and has subsequently pulled apart again.