The continued operation of missions such as Mars Express, Mars Reconnaissance Orbiter, and the ExoMars Trace Gas Orbiter has greatly enhanced our knowledge of seasonal processes on Mars. The most apparent evidence of the importance of seasons on Mars on the large scale is annual variation in the sizes of the Martian polar caps. However, high resolution imaging has also shown that seasonal forcing can lead to small-scale phenomena that are continuously changing the topography and the surface photometry. These phenomena often have no terrestrial analogue and involve complex interactions between seasonal ices, atmosphere, and substrate (surface and sub-surface). Although we now have better understanding of many of these processes (occasionally as a result of laboratory simulation), direct proof of some hypotheses remains elusive. We provide a brief review of the phenomena and list a series of open questions.
