St. Joseph

Silver Beach in St. Joseph was crowded at lunchtime on Saturday when we passed through (more pictures at hshipman).

St. Joseph is on the southeastern shore of Lake Michigan, at the mouth of the St. Joseph River. As at nearby South Haven and New Buffalo (and Michigan City, in Indiana), waves and longshore transport are from north to south, building up sand on the north side of the river mouth jetties. This also used to happen on other side of the lake, at the mouth of the Chicago River.

Geologically, this sand is destined for the south end of the lake, where it will be blown inland to bury 19th century steel mills and freeways under hundred-foot tall dunes.

Straits of Mackinac

We skirted the northeastern edge of Lake Michigan in the dark and wound up in St. Ignace for the night. We stayed on the lake and in the morning I was reminded that we were back on Lake Huron (the eastern extension of Lake Michigan - it's not like there is anything actually separating the two except for the bridge) by the grassy shoreline exposed out in front of the seawalls. It reminded me of the shorelines in Inverhuron and Craigleith, where the falling lake had left similar stranded shorelines.

Grand Sable Dunes

One of the neatest places to find coastal sand dunes is high on the top of bluffs. The Grand Sable Dunes, west of the town of Grand Marais, on the southern shore of Lake Superior are one of the best examples of perched dunes anywhere. Wind blowing across the lake accelerates up the bluff face, eroding the sandy sediments and carrying the sand over the crest where it is deposited to form dunes.

Our visit, and these pictures, captured very little of the actual dunes. The dunes themselves are on top of the bluffs, which consist of sandy non-aeolian deposits. The Google Maps aerial image linked to the title of the shows the dunes better. The bluffs are still very dune-like and I'm sure when D ran down and slogged back up the 300' vertical log slide, he didn't really care that it was a bluff and not a sand dune.

My post-visit homework was fascinating. Like dunes in many places, these have built in discrete episodes, the most recent 300 years ago. The episodes are driven by sand availability, which in turn is driven by the condition of the bluffs. High water levels lead to more rapid toe erosion. More rapid toe erosion leads to active, exposed bluffs. Active, exposed bluffs make more sand available for the wind to blow up the face of the bluff. More sand makes bigger dunes. And when the dunes are growing, they block streams, raising base level and creating ponds, which can create a stratigraphic record of dune building events and of variations in the level of Lake Superior.

We have perched dunes on Puget Sound, too. One set are high on the northwestern shore of Protection Island, north of Port Townsend. My favorite ones on Puget Sound would have been the dunes perched on the high bluffs of northwest Whidbey Island, overlooking the Strait of Juan de Fuca. Unfortunately, these dunes have been pretty much eliminated - leveled and buried under view homes on West Beach Road. They were not as large or extensive as these in Michigan, but they still would have been cool.

Miners Beach

Pictured Rocks National Lakeshore has been on my bucket (beach bucket?) list for along time and, despite this short visit, it remains on it. This trip was too quick and too gray. And a boat would have been nice. Of course, if I ever make it back, I suspect the bugs will also be here - and they were gratefully absent today.

Miners Castle and Beach are among the few parts of this shoreline you can drive to. The brightly colored rocks that form the cliffs are Cambrian sandstones. The sandy beach rose to dunes and a low forested bluff, while rock cliffs rose in the distance. Although water levels fluctuate a few feet on Lake Superior, it isn't like Lakes Huron/Michigan which have chronically fallen over the Holocene, so there aren't a series of beach ridges disappearing into the trees like on Georgian Bay.

Marquette

Apparently, our trip along the south shore of Lake Superior is fated to be gray, and rushed. But we stopped at McCarty Park in Marquette for lunch and to toss the frisbee. This sandy beach is just around the corner north of town and stretches off to the northwest. Bedrock outcrops (I bet they are ancient) created an elegant little tombolo.