A tsunami is a series of large ocean waves caused by a sudden displacement of water. Most are triggered by underwater earthquakes. Volcanic eruptions, landslides, and asteroid impacts can also cause them. The waves travel across the ocean at hundreds of kilometers per hour, often unnoticed in deep water. They grow tall when they reach shallow coastlines.

The 2004 Indian Ocean tsunami killed over 230,000 people in 14 countries. It was triggered by a magnitude 9.1 earthquake off Sumatra. The 2011 Tohoku tsunami in Japan reached heights over 40 meters and caused the Fukushima nuclear disaster. These events transformed how the world prepares for tsunamis.

Warning systems have improved. Ocean buoys detect pressure changes from passing waves. Seismic networks identify potential sources. Sirens and cell alerts give coastal residents minutes to reach higher ground. Vertical evacuation structures and mangrove buffers reduce risk. Education matters. People who know the signs, like the sea receding, can save their own lives. Every minute of warning counts.

Key facts

• Often caused by underwater earthquakes
• Travel fast in deep water
• Grow tall near shore
• Warning systems save lives
• Vertical evacuation and mangroves help