Tsunamis are large sea waves caused by undersea disturbances like earthquakes, landslides, or volcanic eruptions. They are formed when energy from the disturbance travels through the water and causes waves at the surface. The two deadliest tsunamis in recent history were the 2004 Sumatra earthquake tsunami that killed over 200,000 people and the 2011 Tohoku earthquake tsunami in Japan that killed over 18,000 people. While tsunamis cannot be prevented, early detection systems and educating coastal communities on evacuation help minimize loss of life.