Dunes and Dune Succession
The Three Types of Dunes
Parabolic
Parabolic: Also called a Blow-out dune is formed when a loss of vegetation allows the wind to move part of the dune. Their
U-shaped mounds can identify them. The vegetation that covers the dunes is what stabilizes
them. Parabolic dunes are formed when winds cut through linear dunes specifically where foot trails or other disturbances have worn into the existing dunes.
Linear
Linear: The sand blows out along the lake currents and forms linear dunes. The vegetation helps trap the dune to keep it in place.
When rivers move silt and sand into shallow bays the sand is
then carried by the lake currents and winds. They then form linear dunes and vegetation
helps keep them their form. These are roughly parallel dunes. They are formed when
the water levels slowly drop.
Perched Dunes
Perched Dunes: Formed When wind blows sand up a glacial moraine. These are formed when wind blows sand up a cliff made from glaciers that were retreating. They are found mostly in the northeastern shore of Lake Michigan and of Lake Superior. They are usually found 90 to 360 feet above the lake level.
Dune Development.
Four Elements for Dune Development
- Sand
- Wind
- Water Level Fluctuations
- Vegetation