A tsunami's tidal waves batter the shoreline and can destroy anything in their path.
This includes boats, buildings, houses, hotels, cars, trees, telephone lines - and just about anything else in their way.
Once the waves have knocked down infrastructure on the shore the waves continue inland for many more miles - obliterating yet more buildings and homes. As the water rushes across the land it can sweep away yet more trees, gardens, garages, cars and other man made equipment.
Boats have often been hurled into the sky and iron parking metres have been bent to the ground, demonstrating the sheer power of the water.
Tsunamis often hit poorer and less-developed countries around South Asia that are close to the ''ring of fire'' in the pacific ocean - a area with high seismic activity.
Because these countries are poor their buildings are not built strongly to withstand natural disasters such as Tsunamis.
This means that when the water hits the buildings they are easily washed away.
The water leaves a trail of destruction that looks like an enormous bomb has exploded in the area. Entire towns and villages are often destroyed in minutes.
Tsunamis are caused by sudden movements of the earth that happens under the sea. Often the most destructive Tsunamis are caused by earthquakes but causes can also include volcanic eruptions, landslides or even a comet hitting the sea.
Landslides cause tsunamis when the debris falls into the water. This has the same effect of dropping a large stone into a pool - big ripples are created. But when this happens in the sea and it is thousands of tonnes of rock and earth falling into the sea a very large ripple, more like a tidal wave is created. This travels across the sea until it comes into contact with land and a tsunami is formed.
Volcanoes cause tsunamis when there is an eruption. The volcano can either be on land or under the sea, in which case it is known as a submarine volcano. If the volcanic eruption happens on land, the tsunami is caused by debris and lava from the volcano flowing into the sea, which once again causes a bug ripple.
If the eruption happens under water, the enormous power of the eruption sends shudders through the earth and disrupts the water. The water in the sea then breaks into waves which travel across the ocean until they come into contact with a coast. Here, a tsunami is formed.