A tsunami is a large, powerful wave caused by earthquakes or shifts in tectonic plates under the sea. Tsunamis can devastate coastal cities and cause massive damage. While tsunamis cannot be prevented, their damage can be minimized by building tall, strong public buildings for evacuation and constructing dams to catch incoming waves. Major historical tsunamis include those that hit Sumatra, Japan, Portugal, and Indonesia, destroying coastal areas and infrastructure in their paths.