"Nature Guide Journal"

Our transition from the north winds of summer to the south winds of winter affect our climate. The alternate wind directions also affect the shapes of our sand dunes.

The smaller (5-20' tall) "transverse" dunes have ridges that are nearly perpendicular to the steady north winds of summer. The more spectacular (up to 180' tall) "oblique" dunes have ridges that are nearly perpendicular to the blustery south winds of winter, but have overall sand movement at an oblique angle to the dune. In summer, the crest of the oblique dunes move southerly; in winter, the winds shift around to drive the dune crest back northerly.

Our wet winters/dry summers affect the dunes as well. Winter winds are much more likely to encounter wet sand than are summer winds. And, as any sand-castle-builder knows, wet sand sticks together better than dry sand. On high dunes, winter winds sometimes carve free-standing sculptures (called "yardangs") as it cuts into the dune ridge laid down the previous summer.

Further, summer winds may readily sort the dry sand into layers of different color and texture. (Sand grains of different color are usually also of different weight.) The layers are then held in place by winter's wet to be exposed as subtle stripes on the eroding dune face.

Winter rains fill low-lying swales and deflation plains between dunes. Surprisingly, low stretches that appear desert-like to summer visitors may be under several feet of water in winter.

The seasonal differences in wind and rain make it well worthwhile to explore our remarkable dunes throughout the year.