Tsunami waves often look like walls of water and can attack the shoreline and be dangerous for hours, with waves coming from minutes to hours apart from each other.

Tsunamis are comprised of a series of waves.  The first wave may not be the largest, and often it is the 2nd, 3rd, 4th or even later waves that are the biggest. After one wave inundates, or floods inland, it recedes seaward often as far as a person can see so the seafloor is exposed. The next wave then rushes ashore within minutes and carries with it much floating debris destroyed by previous waves. When waves enter harbors, very strong and dangerous water currents are generated that can easily break ship moorings, and bores that travel far inland can be formed when tsunamis entire rivers or other waterway channels.


As a tsunami wave enters shallow water, the wave speed slows and the height increases, creating destructive, life-threatening waves.

In the ocean, normally waves are generated by wind and can be described through their amplitude, which is the height of the wave, and wavelength which is the distance from one wave crest to the other. The wavelength is a factor which distinguishes tsunamis from wind waves: a tsunami wavelength is considerably longer than a wind wave wavelength; it can be more than 200 km long. The wavelength is closely-linked to the sea depth. As the sea depth decreases, the wavelength decreases. At the same time, the height of the wave increases. Near the shore line the wave can assume the shape of a wall, up to tens of metres high, with a massive destructive power. The speed of a tsunami wave can be simply expressed by the formula v= where g is the acceleration of gravity (9,8 m/s2), and h is the depth of the sea expressed in metres.

Tsunamis cause major damage to towns and even deaths when it has reached on land. All tsunamis are potentially dangerous, even though they may not damage every coastline they strike.