Tectonic Plates
The crust is broken into many different pieces which are called plates. These plates float on the upper mantle or the fluid part which is called the asthenosphere (The Earth's Crust, Lithosphere and Asthenosphere. Windows to the Universe). They move about 2 or 2.5 centimeters per year (Understanding Plate Motions. USGS, 24 May 2012). These plates would usually move smoothly above the mantle, but if they get stuck, it can cause pressure and this is the cause for earthquakes to happen. Beside earthquakes, these plates can also cause tsunamis, mountains and volcanoes. Volcanoes and mountains are caused by diverge and converge boundary. Diverge boundary is when the plates move a little further apart, and creates space for the magma to reach the top. This could also create mountains (Plate Tectonics. Wikipedia. Wikimedia Foundation, 17 May 2013). And converge boundary is when the plates come together and overlap each other. So that one of them is under the other which also creates way for the magma to go through. However, mountains could also be formed by converge boundary such as the Himalayas, which is the highest mountain system on Earth (Plate Tectonics. National Geographic. National Geographic Society).
By NASA [Public domain], <a href="http://commons.wikimedia.org/wiki/File%3AHimalayas.jpg">via Wikimedia Commons</a>