Martian crater uplift, coloured satellite image. Uplifts form when the initial crater wall just after an impact collapses under gravity and forces a central uplift of materal from the crater floor. The area surrounding the peak is covered with sand. Ripples on the sand are caused by the wind. Image obtained by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) on 5th August 2009. The width of this image is roughly 1.1 kilometres across.