An underwater explosion, also known as an UNDEX, is an explosion beneath the surface of water. The type of explosion may be chemical or nuclear. They are categorised in accordance with their depth beneath the water's surface, because this has a strong influence on their effects. The heights of surface waves generated by deep underwater explosions are greater because more energy is delivered to the water. Deep underwater explosions are thus particularly able to damage coastal areas, because surface waves increase in height as they move over shallow water, and can flood the land beyond the shoreline. Many of the theories and concepts about these waves are similar to those that are applicable to other types of surface waves, in particular, tsunamis, and waves generated by the fall of a meteorite.