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Unlike body waves, surface waves (also known as long waves, or simply L waves) move along the surface of the Earth. Surface waves are to blame for most of an earthquake's carnage. They move up and down the surface of the Earth, rocking the foundations of man-made structures. Surface waves are the slowest moving of all waves, which means they arrive the last.
A tsunami is a huge wave, usually caused by volcanic or earthquake activity under the ocean, which can eventually crash onto the shoreline. The effects on a community can be devastating. What causes a tsunami? When an earthquake, volcano or landslide happens on the ocean floor, water is displaced. This water forms the start of the tsunami. When the waves reach shallower water: their height can increase by several metres; the shallow water slows the wave; the waves get closer together; It is hard to see that a tsunami is approaching. The most obvious sign is the coastal water retreats just before the waves reach the shore. This is actually the trough of the wave following behind.