A Tsunami is a giant wave that is so strong and tall that it destroys mostly all the buildings and establishments for miles and miles around it. Tsunamis are usually mistaken for tidal waves which they are not. Waves in a Tsunami flow straight and normal water flows in on an angle this is part of what makes a tsunami so powerful. A severe Tsunami occurs about every 15 years. Tsunamis travel at approximately 475 MPH in 15,000 feet of water. In 100 feet of water the velocity drops to about 40 MPH.