Final answer:
A tsunami is usually caused by a nearby underwater earthquake, which displaces water and creates a series of powerful ocean waves.
Step-by-step explanation:
A tsunami usually occurs as a result of a nearby underwater earthquake. When an earthquake happens beneath the ocean floor, it can cause the water above it to displace and create a series of powerful ocean waves, known as a tsunami. This occurs because seismic activity in the earth's crust causes the ocean floor to uplift or subside, resulting in the movement of a large amount of water.
Learn more about Tsunami causes