Deltas
Researchers have found a number of examples of deltas that formed in Martian lakes. Deltas are major signs that Mars once had a lot of water because deltas usually require deep water over a long period of time to form. In addition, the water level needs to be stable to keep sediment from washing away. Deltas have been found over a wide geographical range. Below, is a pictures of a one in the Ismenius Lacus quadrangle.
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Delta in Ismenius Lacus quadrangle, as seen by THEMIS.
Read more about this topic: Ismenius Lacus Quadrangle