A wrinkled patch of land near the volcano's northern region likely formed when blisteringly hot lava oozed out of the summit millions of years ago, hitting water ice at the mountain's base.

Landslides on Mars suggest water once surrounded Olympus Mons, tallest volcano in the solar system

Source: space
Source Link: https://www.space.com/landslides-mars-water-surrounded-olympus-mons-solar-system-largest-volcano