Rock breaks scissors, water weathers rock.

Dear Lake Enthusiasts,

I know what you’re thinking: Rebecca, you haven’t posted in a while so you must be dead.

Well guess what!? I’m not dead (on the outside)! I’ve been having a fun time learning about the shorelines of ancient lakes while travelling around Lake Huron. Now I’ll throw some keywords at you: Nipissing, Algonquin, bluff. Don’t know what those things are? Well too bad, you never will. What is this, an educational blog?

OK, I’ll tell you a little bit. As the Wisconsinan glaciation (a.k.a. the last ice age) ended, giant kilometers-high glaciers began to melt. As they melted they formed large freshwater lakes, the ancestors of our modern Great Lakes. Wow! Neat! I know what you’re thinking — this is stupid, lakes are stupid, everything is dumb. Well wait just one second because I’m about to blow your mind.

Have you ever driven parallel with the shoreline of a Great Lake and thought: wow, that abrupt down-dip in the highway really came out of nowhere? You might have been driving over the shoreline of a an ancient lake! Two prominent shorelines around the Great Lakes were created by ancient Lake Algonquin and Lake Nipissing (not to be confused with the modern Lake Nipissing). These “proglacial” lakes formed approximately 11 000 years ago and 5000 years ago, respectively. In the photo below you can see the white-coloured, dolostone cliffs, which are an erosional feature created by proglacial Lake Algonquin.

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The locations and heights of these ancient shorelines vary depending on the stratigraphy of the area, but on average the Nipissing shoreline is about 4.5 m above the modern shoreline, while the Algonquin shoreline is another 3.7 m above the Nipissing shoreline. This fact brought to you by Wikipedia because I’m sick of reading my stratigraphy guidebook.

In the past, when water levels were higher, wave action formed caves. Today these caves are exposed because the water level is lower. It is because of these high water levels, and the weathering that they induced, that caves formed by wave action may be found in places where there is no water in sight!

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In the past these caves would have looked a lot the caves located in Bruce Peninsula National Park. In the photo below, you will notice that waves have weathered the soft limestone, leaving behind dolostone, which is more resistant to weathering.

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Pretty cool, right? I thought so. And you probably did too since you’re sitting here reading a marginally interesting blog about lakes.

Your neighborhood lake enthusiast and eternal graduate student,

Rebecca

 

 

 

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