Grand Sable Dunes In Winter
February 13, 2009
James says they rode his brother’s snowmobiles back along H58 to this overlook of Grand Sable Dunes in the Pictured Rocks National Lakeshore last weekend.
He has more photos from Pictured Rocks in winter & all seasons in his tremendous Pictured Rocks National Lakeshore set (slideshow) with tons of photos including the pic to the right of the same scene in August.
I was a little surprised to find that I hadn’t written anything about Grand Sable Dunes on Michigan in Pictures. In my opinion, it’s one of the most amazing vistas in Michigan, a broad sweeping dune that arcs along the shore of Lake Superior. It’s a great hike, either from the drive-up overlook (where you can view or visit the Au Sable Light Station) or by walking along the base on the Superior shore just a mile west from Grand Marais. Michigan Tech has a nice writeup on the history, geology and natural character of the Grand Sable Dunes. They’re a perched dune like the Sleeping Bear Dunes in lower Michigan that were formed when:
Glacial ice that melted within the Superior Basin produced many large rivers after the last major readvance, The Marquette readvance, in North America. These rivers deposited millions of tons of debris into many different configurations south of the Superior Basin. The Grand Sable Banks may have originated as a glaciofluvial kame terrace along one of these glacial rivers during deglaciation.
Pictured Rocks then became very dry about 9500 years before present due to the Lake Superior basin draining to the north. The outlets to the east were now the low spots. A north facing ice contact bluff and a platform to the south of it remained in place for 4500 years after deglaciation right around the area where Grand Marais is located today.
Isostatic rebound then occurred about 4000 to 6000 years before present. North Bay began to rise which caused water levels to rise rapidly. In fact, Lake Superior rose to about 40 feet higher than it is today! The rise in lake levels formed Lake Nipissing. Lake levels of Lake Nipissing also began to rise which caused the Grand Sable Banks to become unstable. From this point the formation of a perched dune can explain how the dunes formed from the Grand Sable Banks.
When Lake Nipissing water level rose it caused the Grand Sable Banks to become unstable. In turn, the high water eroded the bluffs which left them exposed to wind. A dominant northwesterly wind blew through the Grand Sable Banks which carried the wind from the bluff to the top of the flat upland. This sand was “perched” on top of the upland, hence the name, “perched dune system.”
You can check out Grand Sable Dunes on Absolute Michigan’s Map of Michigan and check out the Grand Sable Dunes slideshow on Flickr. I have written a fair amount on Pictured Rocks that you might enjoy.