Tsunami

A tsunami is a series of traveling ocean waves of extremely long length (around 200 km) generated primarily by earthquakes occuring below or near the ocean floor. They can also be triggered by volcanic eruptions, landslides from land or on the seabed or by meteorites. Tsunamis are rare and they can cause great damage when they hit a coast.

Source: https://nctr.pmel.noaa.gov/indo_1204.html