Can you imagine an ocean wave the size of a 30 story building swelling up before your eyes? Thats exactly what the people of Sri Lanka saw after an earthquake moved the ocean floor around Sumatra, causing a tsunami. Tsunamis are typically triggered by other natural disasters like an earthquake or volcano eruption. The sudden movement of Earths tectonic plates causes the body of water on top of them like the ocean to be displaced. This is similar to what happens if you drop a pebble into a puddle. The pebble hits the water and causes a rippling effect. When an earthquake happens under the ocean, the tremors from the earthquake ripple outwards and cause the oceans waves to grow bigger the further they move out. The tsunami that happened in India and Sri Lanka on December 26, 2004 was one of the most destructive tsunamis in history. So, to play it safe, whenever there is an earthquake, stay away from nearby oceans!
