Ice Volcanoes on Mars . ... MOC , MGS , NASA Explanation: What causes these unusual cone-shaped features on Mars ? Spanning an average of only 100 meters at the base, these small cones appear near massive Martian volcanoes such as Olympus Mons . ... Given these clues, some scientists speculate that the cones were formed by lava heating ice lying just below the Martian surface . Lava heated ice would vaporize and expand, punching holes in the cooling lava flow as it escaped. ...