Integrative Natural History of Fayette Historic State Park, Part 14: Lake and Headland from a Flaggy Beach | Garden Peninsula, on Michigan's Upper Peninsula, USA

(Updated on April 7, 2025)

At the location featured in Part 10 of this set. So we're still on the Big Bay de Noc shoreline, south of the park's ghost-town site.

The flags in the foreground come from a nearby exposure of dolostone beds of the Byron Formation, and also probably of the Hendricks Dolomite lying above it. Both units belong to the Silurian-period Burnt Bluff Group. That fact is particularly germane because the headland in the distance is Burnt Bluff itself.

I'll offer a zoomed-in view of that landform in the next post of this series. But even here, at this range, the headland sports a feature, a wave-cut terrace and cliff, commonly seen along the shores of the northern Great Lakes. Note how the land's lakeward profile reveals a lower slope below and considerably steeper one above.

This notched profile found in lake-facing bluffs has long been attributed to a "post-Algonquin" highstand of Lake Michigan or one of its proglacial predecessors, when drainage outlets were blocked by an ice sheet or other factors, and the water rose accordingly.

In fact, you can also see an expression of the even higher Lake Algonquin, the expanse of fresh water that existed a little earlier, roughly 11 ka ago. In this case, the wave-cut notch is subtler, but still visible in the middle of the clifftop, just to the left of the jagged tree line.

These old shorelines have been elevated well above their original levels by the process of isostatic rebound. During the Pleistocene, the glaciated portion of North America was pushed downward into the yielding asthenosphere (the semisolid section of the mantle) by the immense weight of the ice sheets. Now freed from that burden, this part of the buoyant continent is rising.

Having said all that, I should note that I'm rather uneasy about the 11 ky date cited in a preceding paragraph. For my book on the architectural geology of the Chicago suburbs, I extensively researched the scientific literature on the evolution of the Great Lakes, and particularly the one pictured here. I found that dates and details and terminology involving the highstands are constantly being reinterpreted, and the timing of high and low water levels varies with each new paper published.

So it's virtually impossible for a person trying to present the results of all this esoteric geochronological square-bashing to the public to get it right for long. Choose any interpretation of the late Pleistocene or early Holocene you wish; it will be superseded six months later.

With that sad understanding, it's still possible to point out the demonstrable effects different highstands have had on the Great Lakes littoral—and how isostatic rebound can actually be detected with the naked eye. And Burnt Bluff's wave-cut cliff is certainly the place to understand such things.

To see the other photos and descriptions in this set, visit my Integrative Natural History of Fayette Historic State Park album.

Taken in: United States / Michigan / Fairbanks Township / Fayette (show map)

Taken on: September 7, 2007

Tags:

geology

landscape

parks

rock

rocks

stone

Michigan

Upper Peninsula

Garden Peninsula

Fayette Historic State Park

Lake Michigan

Burnt Bluff

dolostone

beach

shoreline

surf

Big Bay de Noc

headland

isostatic rebound « less

Sets appears in: • Grab Bag of All Things Silurian • Integrative Natural History of Fayette Historic State Park | Michigan more » • Natural History: Michigan • Ortsinn: Landscapes & Localities • Rock Forms, Rock Formations • Shorelines « less

Camera: NIKON COOLPIX S4, f/4.0, 1/293 sec, 6.3mm, ISO 50 (more info) (hide info)

Camera:	NIKON COOLPIX S4
Aperture:	f/4.0
Exposure Time:	0.003 sec (1/293)
Focal Length:	6.3mm
ISO:	50
Exposure Bias:	0 EV
Flash:	Off, Did not fire
Exposure Program:	Program AE
Metering Mode:	Multi-segment
White Balance:	Auto
Color Space:	Uncalibrated
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