Tsunami comes from the Japanese for "harbor wave," unleashed when an underwater disturbance sends a series of massive swells toward shore. This film examines two of the deadliest on record. In 2011, an earthquake off the coast of Japan triggered a tsunami that killed more than 15,000 people, swamping coastal towns and crippling the Fukushima nuclear plant. The worse case came on December 26, 2004, when a tsunami born off Sumatra struck without warning across South Asia, killing an estimated 280,000 people in 14 countries. Survivors describe the water arriving in minutes with no time to run, and experts break down the seismic mechanics that turn an ocean floor rupture into a wall of water. The film moves between eyewitness testimony and geological explanation, showing how warning systems failed in 2004 and what changed afterward. It is a straightforward account of how these two disasters unfolded and why the death tolls reached the scale they did.