The edge of the north circumpolar sand sea is bounded in many places by dunes that are larger than their neighbors and set off from them somewhat, “framing” the erg. The frame dunes (arrow) are thought to grow by the addition of sand-sized material from the surrounding plains and hence they are larger. Large dunes migrate more slowly than small dunes, so the frame dunes get left behind the edge of the erg as it migrates.
Location: Latitude 78°, Longitude 89°. Viking photograph 519B36, NGF orthographic version, minus-blue filter.