Many types of craters exist on Mars. Most are generated by impacts of asteroids and comets.
In this area though, we think these craters may be due to steam explosions. This happens on the Earth when hot lava runs over icy ground.
Written by: HiRISE Science Team (6 November 2013)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_033252_2070
Image: NASA/JPL/University of Arizona