Tsunamis are not killer waves or rogue waves, they're strong displacements of water. The height happens only at the shore because the sea floor rises up to meet

Tsunamis are not killer waves or rogue waves, they're strong displacements of water. The height happens only at the shore because the sea floor rises up to meet the shore. At sea, one probably doesn't even see anything abnormal as the wave ( more accurately, the pressure crest ) rushes past underwater.