These plates can be as large as entire continents , and move independently of the plates around them, much like slabs of polar ice gliding over the ocean's surface, thus spreading as well as colliding together . The major relief features can be divided simply into two broad categories, the continents and ocean basins . If the oceans were drained, we would see that the continental shores are actually covered by ocean water. The parts of the continents covered by ocean water are called continental shelves . The mountain-making in the active belts grow through two very different processes.
Volcanism is the formation of massive accumulations of igneous rock by extrusion of magma .
Tectonic activity is the breaking and bending of the earth's crust by forces below the earth's surface . Parts of the crust raised by tectonic activity form some of the mountains, valleys, and plateaus we see on the Earth's surface. Active mountain-making belts are narrow zones along continental margins and referred to as alpine chains that stretch across the Earth's surface in smaller curves called mountain arcs . The arcs are linked to form two principal mountain belts. The first is the circum-Pacific belt , which rings the Pacific Ocean, stretching from South America through North America, across Japan and eastern Asia, into the south Pacific.