The tsunami is a tidal wave, which may arise for example due to a deep-sea earthquake, dramatic volcanic eruption, landslide or asteroid falling into the sea. In the open sea a tsunami travels 500-900 miles per hour. Wave height in the deep sea is usually less than one meter. However, when the wave approaches shallow water, it can raise up to 50 meter high wall of water when it pushes on the shore and destroys everything that end up on its way.
Large asteroid or massive landslides can send off a huge mega tsunami that can be hundreds of meters high. There are different terms used for a tsunami depending on the geographical location.
Earthquake magnitude must have a minimum of seven on the Richter scale, to develop into a tsunami.