Crustal movements under the oceans can displace water bodies, producing huge waves, called tsunamis, as high as 30 meters.
Giant waves can be produced by three types of phenomena:
1) Volcanic eruptions inject tons of lava into the ocean floor, generating devastating waves.
2) Undersea earthquakes displace the ocean's crust, pushing up the body of water.
3) A gas bubble appears at the bottom of the ocean, with the same effect as a blast.