Wall Of Water: The Tsunami Explained

During a tsunami the ocean suddenly floods the coast, smashing everything in its path, and then just as quickly recedes.

Large quakes are the main cause of tsunamis, but they can also be sparked by other cataclysmic events, such as volcanic eruptions and even landslides.

During a strong quake, oceanic plates can lurch many metres and rupture the ocean floor.

This movement can suddenly move a massive amount of water.

:: Read about today's quakes in Indonesia

Major quakes that rupture the ocean floor are usually shallow quakes occurring at a depth of less than 44 miles (70km).

The 9.1 magnitude quake that caused the devastating 2004 Boxing Day tsunami was 18 miles (30km) below the seafloor.

The movement of the quake can also affect the likelihood of a tsunami occuring.

The vertical movement of some earthquakes can cause the seabed to heave and displace water vertically, sending towering waves racing toward shores.

The 2004 tsunami, which killed nearly a quarter of a million people, and the 2011 disaster in Japan were both caused by these "mega thrust" quakes. Read More