During periods in Mars’ history when the planet had greater axial tilt, shifts in atmospheric circulation may have favored the extensive accumulation of snow in some locations. Protonilus Mensae is just such a site of extensive glaciation.
HiClips from HiRISE (High Resolution Imaging Science Experiment) onboard the Mars Reconnaissance Orbiter (NASA). Narrated clips are labeled as "HiClips" plus the title. All others are non-narrated.