WHY does water recede from the coast before a tsunami hits? In particular, a wave is formed that differs from an ordinary wind-driven wave in that it is enormously long. While ordinary
wind-driven waves are 100-200 meters long, tsunamis can be tens or hundreds of kilometers long. The most significant metamorphosis occurs with a tsunami wave when it "bumps" into shallow water, closer to shore. Its speed, which in the open ocean was
comparable to the speed of a jetliner (800 km/h), decreases, but its height sharply increases. However, we should bear in mind that in addition to the high crest of the wave rushing towards the coast there is the "sole", that is,
the lowest point below the level of calm water. If the "sole" attacks the shore first, the coastal water level drops,
exposing meters or even kilometers of the bottom.
