Martin Gabriel / Peak of Spitzkoppe reflected in ephemeral pool, wet season. Damaraland, Namibia

Doug Wechsler / Pothole in the Fiery Furnace canyons, Arches National Park, Utah, USA. June

Doug Wechsler / Pothole in the Fiery Furnace canyons, Arches National Park, Utah, USA, June

Michael & Patricia Fogden / Spitzkoppe granite outcrop in southern Damaraland with ephemeral pool after good rain, Namib Desert, Namibia

Doug Allan / Ephemeral 'sand river' bed in dry season, Hoanib, Namibia

Doug Allan / Ephemeral 'sand river' course in dry season, NW Namibia

Doug Allan / Ephemeral sand river-bed, Hoanib, Namibia