40. Arid Environments and Wind as a Geomorphological Agent

Photo 70: Sand Dunes in the Rocky Mountains close to Jasper, Alberta. 2011-05-19

Aeolian Processes

After water, karst, and glacial erosion, it is important to look at wind as erosional force. Wind sets in motion grains of sand and clay, which can erode surfaces in the case of wind abrasion (sandblasting) and can form landforms and landscapes during surface creep (in the case of larger particles and rocks) and deflation (in the case of fine particles). Wind is only an erosional force when it picks up grains of sand. Some main landforms of wind erosion are yardings, aerodynamic ridges in rock parallel to the main wind direction, and ergs, which are aggradational sand seas in desert areas that contain about 95% of all Aeolian (wind-related) sand.

Sand Dunes

Photo 70 shows, to my surprise, sand dunes in the Rocky Mountains. Dunes are aggradational landforms of deposited sand. Deflation moves sand and finer particles. When sand reaches the impact threshold, it bounces back into the air, thus being able to travel great distances. Sand accumulates in areas of slower wind speeds and around existing landforms. In photo 70, the sand dunes are formed against the windward side of a mountain. Sand dunes themselves have a windward side too, called backslope, a top or crest, and a leeward side or slip face. Photo 71 shows an Aeolian feature called blow-out, where the wind has carved the surface in a way that is like a Barchan dune.

The sand dunes in the location of the photos are fed by the river across the road, which is full of water during spring runoff and quite empty during fall and winter. Sand from the river’s bed has formed the dunes, in combination with the wind. The wind is aided by the surrounding landforms (mountains) that have directed the wind in a favourable way for dune formation.

Photo 71: Blowout in Sand Dunes. 2011-05-19