According to National Geographic, tsunamis can be caused by underwater landslides or volcanic eruptions, and are generated from the epicenter of the shift. The movement of tectonic plates causes water displacement, which creates a rolling wave that can travel over water at up to 500 miles per hour.
Because of the displacement that occurs when a tectonic plate shifts, one major signal of an approaching tsunami is the drawback that occurs a few moments before the tsunami wave arrives. Drawback refers to the period when the shoreline recedes dramatically, exposing various sea life, such as fish and plants. The Pacific Tsunami Warning system, headquartered in Hawaii, is responsible for sending warnings to coastal cities and countries. They use seismic equipment and water level gauges in order to determine any undersea tectonic activity.
Tsunamis cause major damage in two ways. The first is with the pure force with which the water is moving. The second is by the volume of water moving at such a high speed. They only gain momentum, width and height as they approach the shore. However, once these powerful waves hit shallower water and the coastline, their power and speed begin to decrease. Tsunamis usually hit land in a series of waves that can span over several hours.