Tsunami waves do not resemble normal sea waves , because their wavelength is far longer . Rather than appearing as a breaking wave , a tsunami may instead initially resemble a rapidly rising tide , and for this reason they are often referred to as '' tidal waves '' . Tsunamis generally consist of a series of waves with periods ranging from minutes to hours , arriving in a so-called " wave train " . Wave heights of tens of metres can be generated by large events . Although the impact of tsunamis is limited to coastal areas , their destructive power can be enormous and they can affect entire ocean basins ; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with at least 290,000 people killed or missing in 14 countries bordering the Indian Ocean
2004 Indian Ocean tsunami
2004 Indian Ocean earthquake and tsunami
Tsunami Warning, Education, and Research Act of 2014