Nili Patera

At the summit of the low-relief shield volcano Syrtis Major, the caldera known as Nili Patera hosts a remarkable field of barchan-like dunes. The rugged knob to the north of the dunes is probably a breached volcanic cone representing one of the last eruptive events from this caldera. The graben seen at the top of the image are common features on volcanoes and are caused by collapse of the surface after an eruption empties the magma chamber below.