Algonquin's Natural History: The Canadian Shield and Wisconsonian Glaciation

Most working scientific theories of the age of the earth suggest that the planet was formed about 4.5 billion years ago, though we have no conclusive evidence of anything on this planet to demonstrate that she is older than 4.2 billion years of age.  The oldest rocks we have are from one of the most stable and large masses of continental core of anywhere on the planet, the Canadian Shield.  Radiometric dating has been used to determine that some gneiss near Great Slave Lake in the Northwest Territories of Canada is close to 4.2 billion years old, pre-dating the creation of life itself on our planet.  Billions of years of erosion have mostly knocked away any great heights that would have covered what now juts up through the earth.

Come back in September for some pictures!

The portions that are exposed today are incredibly tough stuff, having endured travels over the globe, a lot of weather, multiple ice ages, and even being under oceans at certain points in time.  While they are hardly as grand as the Rockies or other such mountain ranges, what does remain of the Canadian Shield mountains, such as the Laurentians and Adirondacks, are far from unimpressive, considering as how they are often taller and more rugged than much younger mountains in the Appalachians and Ozarks, which have been worn down to the same size in a much smaller time scale.  In Algonquin, the mountains often have a prominence of about 700 feet, resting on a base of about 1,000 feet, enough to give a hefty hiker heart problems and enough to change weather patterns in the area, complete with a lusher western region and a drier rainshadow to the east.  We can only imagine what these would have looked like over a billion years ago, when they might have well exceeded 40,000 feet in height.

Come back in September for some more pictures.

Much more can be said about the Canadian Shield, but that is content best left for future posts.  The important thing to leave here is that Algonquin has very old rocks, young as far as the shield goes (between a billion and two billion years old, but there are probably much older rocks that have yet to be found in her depths), rocks that are often exposed and make the landscape very rugged, akin to much more vertical terrain like the Sierras or Rockies.  That said, Algonquin also has very grand forests, and most trees require at least a little bit of soil on top of the bedrock in order to survive.  So, what lies on top of the bedrock?

More rock!  Here and there are ancient traces of limestone from hundreds of millions of years ago.  Young by Shield standards, but remnants of a very different undersea tropical era for Algonquin.

Thanks again to the McElroys, who have a wonderful article on this little limestone peninsula on Cedar Lake at  http://www.mcelroy.ca/notes/brent_limestone_cliff.shtml.

Here we see some rock that looks out of place in Algonquin, but would very much be at home, say, in the Niagara Escarpment or in the Allegheny Mountains.  While the glaciers of several ice ages did a pretty good job of liberating the Shield rocks by scraping the ground bare, some areas managed to survive the onslaught.

That said, when the glaciers did retreat they left some stuff behind, sometimes ground up into a nice till and even dragged north from areas further to the south that they also did a number on.  Glacial till, as we mentioned a few posts back, makes for lovely forests and terrible crop field.  It is gray, sandy feeling, and often quite cold even in the summer and under full sun.  The glaciers left a bit more than till around, however, namely sand and water.  So what's the deal with those glaciers, anyway?

Source: USGS, at  http://esp.cr.usgs.gov/info/eolian/task2.html.

The last major ice sheet that covered North America is known as the Laurentide Ice Sheet, and was over 5,000 feet thick in some interior portions of its range.  For a long time, it would slowly advance southwards, melting a little in the summer, growing back bigger and better in the winter.  Whenever it melted it sent A LOT of water towards the ocean, normally either right into big blue or down the primordial versions of the Columbia and Mississippi rivers.  Along with immense volumes of water would rush small-grained silt, clay, and lovely, lovely sand.  The loess areas seen on the map below are the results of this material blowing around in the dry winters when the floods diminished.

Eventually, about 8,000 years ago, the Laurentide sheet kept melting north as the planet warmed up closer to where we sit today.  While the Mississippi continued to take quite a load of melt with it (you can find many rocks from Lake Superior almost all the way down the Mississippi on her banks), new outlets opened up, namely various predecessors of the Great Lakes-St. Lawrence watershed.  One of these outlets was through the north of Algonquin, and it cut all sorts of interesting lakes, canyons, and such in its path.  It also left behind sand, sand that is without a doubt the best in the universe.  It has such a lovely consistency and softness that it became the sand of choice at the recent Olympic games in London.  Britain might not have the sand for volleyball, but Ontario came through for them.

Come back for pictures of this amazing sand.  I will have lots of them.

Then the glaciers left... and were followed by conifers, birches, willows, and... cacti?