What is a Tsunami?

A tsunami is a series of extremely long waves caused by a large and sudden displacement of the ocean, usually the result of an earthquake below or near the ocean floor. This force creates waves that radiate outward in all directions away from their source, sometimes crossing entire ocean basins. Unlike wind-driven waves, which only travel through the topmost layer of the ocean, tsunamis move through the entire water column, from the ocean floor to the ocean surface.

Source: The science behind tsunamis | National Oceanic and Atmospheric Administration

Where do tsunamis occur?

A tsunami can strike any coast (ocean, lake or even river) at any time. There is no season for tsunamis. Tsunamis typically happen where there are large faults that can generate large earthquakes. Most of these large faults are around the Pacific Ring of Fire. However, any active fault that crosses water may be capable of generating a tsunami. Other causes of tsunamis include landslides and volcanic eruptions which can happen far away from any ocean coastline.