Blowing sand and surface winds in the Pisco to Chala Area, Southern Peru

One of the unique features of the present study was the mapping of the direction of sand movement (small arrows in Plate 1) which indicates the direction of prevailing surface winds. Offshore, these winds have a nearly constant south-southeast direction. Onshore, the winds blow in great clockwise-sweeping arcs due to frictional drag and other forces as the wind moves diagonally from the ocean over the uneven ground surface. However, there is some modification of the wind direction by topography, one good example being the obvious partitioning of the wind around both sides of Cerro Huaricangana (elev.=1725 m) in the center of the area (Plate 1b). But the most interesting wind pattern occurs in an area of subdued relief and low elevation near Ica (elev. approx. 400 m), where the sands converge on the Ica sand mass from nearly opposite directions, that is, from the northwest, west, southwest, and southeast. The wide angle sweep (140°) of incoming sands here is believed to be unique in the world. A Landsat image was used to determine how this unusual wind pattern could develop (see Fig. 9), but the extreme local rotation of the winds is not fully understood. One idea proposed here by the author is that the surface/near-surface winds move as horizontal vortices, not in streamlines as is generally assumed, and it is the interaction of the vortices and the land surface that causes the pervasive clockwise swing in wind direction.