Dune and swale complexes are series of roughly parallel dunes that
form as the water level of the lake gradually drops. These dunes
may form in bays which are gradually being filled in by sand deposits.
Wilderness State Park on the north shore of Lake Michigan has more
than 100 dunes in a dune and swale complex.
The complex is produced
by a series of foredunes forming as the beach "grows"
out into the lake. (See Foredunes for
foredune descriptions and formation.) Each new foredune eventually
cuts off the sand supply to the inland dune. The result is a series
of low dunes, generally less than 3 meters (15 feet) in height.
Dune and swale in Wilderness State Park. The wet
area in the foreground of the photo is the interdune swale; behind
the swale is the low, vegetated foredune ridge. (Photo from R.
Swales are the troughs or low-lying land separating the dune ridges.
Originally wet and marshy, the swales dry out over time. The progression
from wet to dry swales can be seen as one moves further inland.
Dune vegetation in the
complex also reflects the age progression of the dunes. Pioneering
species grow on the active foredune. Inland dunes have progressively
older and more established ecosystems on them.