Development of scarps in Seth. a) Scarps were imperceptible on December 2, 2014. b) Two scarps (indicated by red arrows) were observed on January 23, 2015. c) One scarp had retreated by more than 10 m in the following two weeks; the other feature had become less distinguishable. The yellow arrows point to a common boulder in all images as landmark. The observation in (a) was taken at the phase angle of 92◦ with the pixel resolution of 0.52 m. b) was taken at the phase angle of 93◦ with the pixel resolution of 0.48 m. c) was taken at the phase angle of 95◦ with the pixel resolution of 0.66 m (Table A.1). The Sun is projected toward the bottom of the image in (a), in the opposite direction as in (b) and (c).