According to National Geographic, tsunamis are caused by underwater landslides, volcanic eruptions or the impact of large meteorites falling into the ocean. About 80 percent of all tsunamis happen within the Pacific Ocean's "Ring of Fire:" a geologically active area where tectonic shifts make volcanoes and earthquakes common.
The vast majority of tsunamis happen because of earthquakes and underwater landslides. The energy from an earthquake displaces ocean water, which causes the formation of waves that travel over long distances at varying heights. These waves, called wave trains, are destructive when they reach the shore, and may be compounded by successive waves. The size of the waves depends largely on the magnitude of the earthquake and the shore's proximity to the epicenter of the earthquake.
It is common for tsunamis to appear on the shore as very strong and fast tides instead of giant breaking waves. However, there is also a possibility that a tsunami can quickly escalate into bigger waves that cause destruction of life and property with floating debris and the impact of the water. As a result, regions that are prone to tsunamis use early warning systems that allow people to seek higher ground when there is seismic activity in the region.