Google Earth Image
Blowouts and Dune Formation
Blowouts are saddle shaped or U shaped depressions in a sand dune, caused by wind action on areas where the dune has been destabilized. Destabilization of a dune occurs when the vegetation that stabilizes the fore dune is lost, or when exceptionally strong winds blow sand inland, covering stabilizing vegetation. Loss of vegetation can be caused by wave action on fore dunes, decreases in water tables, extended droughts, fire, clearing for construction, or trampling by humans, animals, etc. Although they generally remain small, blowouts can expand to kilometers in size.
Blowouts which originate on the crest or windward face of parallel dunes can be rapidly formed by the wind into narrow channels and, ultimately, into deeply carved parabolic dunes. Parabolic shaped dunes are characterized by crests pointing upward with trailing “arms” anchored by vegetation, and often, spectacular peaks. It is the combination of interwoven parallel dune ridges and parabolic dunes, which characterizes the shoreline topography from Indiana, northward to Ludington, Michigan.
Ecological Succession
In time, seeds of suitable pioneer species, such as marram grass, are blown in and become established. These early, hardy plant species stabilize the dunes and prevent them from moving further. As they propagate, die and decay, the soil becomes more mature, and new species of less hardy plants such as dune willows, junipers, milkweed and thistle take root. This process of ecological succession continues until the dunes are converted to woodland.
Tread Lightly
Please tread lightly during your visit. Dunes are fragile ecosystems. As sturdy as they seem, dune plants are especially sensitive to human disturbance. Walking on them may cause destruction of surface vegetation and root die-off. This exposes the dune to wind erosion, and damages the integrity and preservation of a stable dune. Insofar as possible, stay on established trails. Where you cannot, choose an approach that does not lead you directly up the backside of the dune. If you cannot avoid a steep uphill slope, walk diagonally across the slope rather than directly uphill. If you are traveling with a group, take separate routes. You will put less stress on vegetation and soils this way. Please do not enter into the blowout area itself.
Sanctuary Woods
This area is located in Sanctuary Woods Preserve. This park occupies approximately 40 acres in the northwestern corner of Laketown Township, in western Michigan. Parking is available off 66th St between W 32nd St and 147th Ave. It is open from 6:00 am to dusk and features well-developed trails through a back dune forest, great views of Lakes Macatawa and Michigan, bird-watching, abundant wildlife, the track bed of the old Grand Rapids, Holland & Chicago Railway, and several high quality caches!
How to Log This Cache
To log this EarthCache, post your log with a picture of you/your team with the blowout in the background. Do not post answers to the below questions with your log! Send an email to me, with a description of the vegetation inside the blowout, an estimation as to what stage of plant succession it is in (early, middle, late), and an estimate of the height of the crest above lake level.
References:
- Blowout, downloaded from Wikipedia 25 May, 2009 en.wikipedia.org/wiki/Blowout_(geology).
- Dune , downloaded from Wikipedia 25 May, 2009, en.wikipedia.org/wiki/Sand_dune.
- Coastal Dunes, Michigan Department of Natural Resources, downloaded 26 May, 2009 from www.michigan.gov/dnr/0,1607,7-153-10370_22664-61314--,00.html.
- A Guide to Sand Dune and Coastal Ecosystem Functional Relationships, Joan Peterson & Dr Eckhart Dersch, Michigan Cooperative Extension Service. Extension Bulletin E 1529 MICHU SG 81 501.
- Low Impact Skills for Coastal Dunes, Calvin College, downloaded 26 May, 2009 from: www.calvin.edu/academic/geology/coastaldunes/processes/low_impact.htm.
Congratulations to gvsu4msu and Johngie upon their joint F2F!