Just check out the specs on that hole..
Valles Marineris: Facts About the Grand Canyon of Mars
"Valles Marineris is a system of canyons that spans 2,500 miles (4,000 kilometers). At some points, the canyon is 125 miles (200 km) wide. Regions can reach depths of 6 miles (10 km). "
http://www.esa.int/images/valles_3d_H.jpg
It's a monster! And, the theory is... Wait for it..
It was blasted out, by an electric arc!
And it didn't take all day either..