Billions of years ago, a giant landslide cascaded down the slopes of the largest mountain in the solar system—Mars’ Olympus Mons. When all this material fell into the water of Mars’ (probable) ancient ocean, it created a towering tsunami stretching between 25 and 43 miles long that crashed against the shore of the planet’s northern hemisphere.
A new study in Planetary and Space Science identifies the remnants of this long-ago event. The landslide-induced tsunami would have required a large body of water, yet more evidence for the case in favor of the existence of a long-disappeared Martian ocean.
Martian tsunamis are not a new idea. In 2015, researchers showed that impactors from space had splashed into the planet’s ancient ocean and kicked up giant waves. The newest findings could also help planetary scientists pin down how big the ocean might have been.
Landslide-generated tsunamis are common on Earth, says Fabio Vittorio De Blasio, a scientist at Italy's University of Milan and the author of the new research. To show the same thing could’ve happened on Mars, De Blasio studied satellite images of the planet’s topography, more specifically the remains of the enormous landslide. At 370 to 430 miles long, the scar is "probably the largest single landslide deposit on Mars," he says, and possibly the longest landslide in the solar system.