A dune is a mound of sand that is typically formed by the wind, and are usually found on beaches like this one, or in the desert. Dunes generally form when wind blows sand into a sheltered area behind an obstacle. Dunes grow as grains of sand accumulate.
Every dune has a windward side and a slipface. A dunes windward side is the side where the wind is blowing and pushing material up. A dunes slip face is simply the side without wind. A slipface is usually smoother than a dunes windward side.
Dunes can also be formed by strong currents beneath the water. Underwater dunes, called subaqueous dunes, are common in the ocean, rivers, and canals.
Shapes of Dunes
Dunes can be very large geographic features or just small bumps. Most sand dunes are classified by shape. There are five major dune shapes: crescentic, linear, star, dome, and parabolic.
Crescentic dunes are shaped like crescents, or the shape of a wide letter C. The wide side of a crescentic dune is its windward side, with a small, semi-circular slipface on the other side. Crescentic dunes are the fastest-moving type of dune, and also the most common.
Linear dunes form straight or nearly straight lines. Some linear dunes are shaped like a wiggling snake, with regular curves. Linear dunes develop where wind pressures are nearly equal on both sides of a dune.
Star dunes have pointed ridges and slipfaces on at least three sides. Star dunes develop where winds come from many different directions. The sand dunes of the Sahara Desert ergs are star dunes.
Parabolic dunes are similar to crescentic dunes. Their shapes are roughly the same, but the slipface of a parabolic dune is on its inward side. Parabolic dunes are also called blowouts, because winds blow out the center of the dune, leaving just a rim on the outside.
Dome dunes are the rarest type of dune. They are circular and do not have a slipface. The wind can blow material onto the dune from any side.
At the posted coordinates, examine the dunes and send the answers to the following questions:
1. What shape of dunes are present here?
2. Do you think these dunes are natural or man-made, and why?
3. These dunes are helping to stop what from happening? (Hint - starts with the letter 'e')
4. The dunes are also helping to keep what away from the boardwalk?
5. Notice if it is windy today, and if so, what direction the wind is blowing.
6. If the wind always blows in this direction, what shape will the sand dunes change into over time from the 5 options listed above?
Once you have messaged your answers to the Cache Owner, you may log your find. Please do not post the answers or images of the signs with your Found It log.