Tsunamis are one of the dangerous and destructive phenomena that are still not fully understood by specialists. What is this phenomenon, why does it occur, and what consequences does it cause? We will also consider the classification of tsunamis and the most well-known cases in history. In translation from Japanese, the word "tsunami" denotes a wave in a bay. In other words, these are large waves that are formed as a result of the strongest impact on the depth of water in the ocean or sea. The main difference of this natural phenomenon from ordinary high waves lies precisely in the nature of their origin. While ordinary waves are formed only on the water surface, tsunamis cover its entire depth. The size of the waves depends on the volume of the body of water. The average height of the waves is 10-40 meters. Tsunamis can travel at speeds of up to 900 km/h. They can take on various forms. Often, they consist of multiple waves that hit the coastline with a certain interval of time - from 3 minutes to 2 hours.