Martian winds are presently redistributing dust particles. Shown are what are probably plumes of dust being raised by northerly winds from the surface of a series of old volcanic flows. The plumes are huge, up to 20 km long and 1 km high, similar in size to some terrestrial dust plumes. (Location: Latitude –21°, Longitude 117.5°, in southern Syria Planum.
Viking photograph 056A24, NGF orthographic version, clearfilter. See Appendix for an explanation of Mars photograph nomenclature.)