(CNN) -- The devastating wall of water that struck Japan in March was the result of at least two waves that combined to create a more powerful tsunami, U.S. scientists said Monday.
Ocean ridges and mountain ranges below the surface of the water channeled the waves created by the 9.0 magnitude earthquake off the coast of Japan, bringing them together far out at sea to form a "merging tsunami," according to researchers from NASA and Ohio State University.
The earthquake and tsunami together killed 15,840 people, according to the most recent death toll, and set off a nuclear crisis at the Fukushima Daiichi plant.
Satellite data have enabled the researchers to come up with an account of the formation of the tsunami and its destructive force.
"Nobody had definitively observed a merging tsunami until now," Y. Tony Song, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement.
The results of the research could help predict the risks from tsunamis in the future.
"We can use what we learned to make better forecasts of tsunami danger in specific coastal regions anywhere in the world," said Professor C.K. Shum of Ohio State University.