On Friday 11 March 2011, an earthquake measuring 9.0 on the Richter scale triggered a tsunami that devastated parts of coastal Japan.

Japan's Tsunami: How It Happened investigates the science behind the earthquake and tsunami. The programme follows Professor of Geological Sciences Roger Bilham - who arrived in Japan days after the earthquake struck - as he sets off to view the devastation from the air.

The earthquake moved Japan 12 feet closer to the USA. The earth was knocked off its axis and the rate of the earth's rotation was changed. This was one of the biggest earthquakes ever measured; the ground along the east side of Japan dropped by almost 10 feet, making the tsunami catastrophic.

The documentary also follows renowned journalist Callum Macrae as he travels to the north, where the towns of Sendai and Ofunato used to be bustling fishing villages. Here he views the destruction first hand and meets the locals struggling to cope in the aftermath.

Japan lies on the Pacific Ring of Fire where the Pacific Ocean plates meet the land. The ocean floor dives beneath the volcanic chain of islands that make up Japan. And when the tension builds up between the two plates the energy is released as a massive earthquake.

The programme provides the science and analysis to explain why this happened where it did, and why it was so devastating, hearing from the scientists at the Pacific Tsunami Warning Centre in Hawaii who tracked the deadly wave as it raced across the pacific, and scientists at the Tsunami research facility in Oregon who study the dynamics of earthquake-generated Tsunamis.

As Japan is lives with the consequences of this terrible force of nature, the film reveals how it has changed the country forever.