Watch Horizon Season 42 Episode 9 Online

In this documentary on earthquakes, Horizon starts with the worst natural disasters of all time in December 2004. The cause of so much devastation was the most powerful kind of earthquake on the planet - a megathrust. Megathrust earthquakes only occur on a particular kind of fault. Scientists have now discovered that just such a fault could cause a huge megathrust earthquake and tsunami right off the coast of North America.