Building Dunes Part 1: Where sand goes from the beachWritten April 21, 2013, published in late April, 2013, all photos by Kathleen Sayce.
|Originally used as an illustration of black sand on a winter beach, this also shows sand blowing from left to right into the dunes, to build up the elevation and the width of the fore dune––the dune immediately adjacent to the beach.|
In summer, strong northwesterly winds blow dry sand along the open flats and up into the dunes. In winter, with strong winds from southerly directions, sand is also blown/washed into the dunes, some of it carried on salt spray or at the surf edge. I haven’t set out measuring sticks to see which season’s winds (summer or winter) move more sand, but one big storm can deposit six inches of sand on a dune top. From the air it looks like a water cannon plastered the dunes with sand slurry. The net effect is to build a dune at an angle to both wind directions, one that parallels the beach.
|Winter storms blow build fresh layers of black sand into dunes over beachgrasses, at Benson Beach, Cape Disappointment State Park. Next spring these grasses will send rhizomes into the sand and bind it, while their leaves sprout above the new level.|