At least some of the barchan dunes in the north circumpolar erg are currently active and moving. Shown here are barchans that have had sand blown off them and onto the frost-covered surrounding plain. These barchans are very large (up to 2 km) and would be termed “mega-barchans” if they were on Earth.
Location: Latitude 77.5°, Longitude 225°. Viking photograph 544B05, NGF orthographic version, minus-blue filter.