How do tsunamis form and travel across oceans?

The answer

Tsunamis are generated when large volumes of ocean water are displaced, typically by undersea earthquakes, volcanic eruptions, or submarine landslides. In the open ocean, tsunami waves can travel at speeds up to 800 kilometers per hour with wave heights of less than a meter, making them nearly undetectable to ships. As they approach shallow coastal waters, the waves slow down and compress, building to devastating heights of 10 meters or more. The 2004 Indian Ocean tsunami was triggered by a magnitude 9.1 earthquake and caused over 230,000 deaths across 14 countries.