Fresh off his triumphant Elk (not moose) show, artist and weatherman Bruce Laidlaw is at it again. This time he asks, Do other people name their favorite rocks?
Our name for the rock in front of our cottage is Tiger Rock. We learned that name from the granddaughter of the woman who sold us our place. The granddaughter visits Tiger Rock when she is in the area. She told us that the huge rock in front of the Good jetties is Big Bertha. With the water as low as it is, Tiger Rock can be quite a navigation hazard. When we bought our place, I could stand on Tiger Rock and the water would come up to my chin. When I stand on it now, the water is just half way up my calves.
This is how we mark the rise and fall of the Great Lakes. We measure them against our own beloved places and our own selves. The Army Corps of Engineers can calculate all it wants, but when we stand on tiptoe atop Tiger Rock – or Turtle Rock or Gull Island or Big Bertha – day after day, all summer long, year after year, we know whether the lake level is rising or falling and by how much.
Of course, the lake’s life is long and ours are short. It remembers the time before time, when it covered all the land Around Here to a great depth. It remembers rushing rivers of glacier melt. It remembers receding to a much smaller lake, the sand of its bottomlands blowing eastward to make the great dunes along the old shoreline. It remembers rising again, and falling, rising and falling. The lake, and the rocks under it, will be here a long time after we’re gone. Or perhaps not . . . but when they are gone, we will be gone too.
From Geological and Natural History of ACNA, posted at the Antrim Creek Natural Area (and almost certainly written by Prof. Charles Cleland):
Geologists have identified and named several important lake levels. The oldest and highest level is Lake Algonquin, whose beach is evident east of the Old Dixie Highway. During the Lake Algonquin period the entire Natural Area was submerged. Later, a change in the drainage route of the Great Lakes caused a sudden drop (by geological standards) in the level of Lake Algonquin to well below the current level of Lake Michigan and exposed the lake’s bottom lands. During this period, known as the Lake Chippewa phase, many of the famous dunes along the eastern shore of Lake Michigan were formed by the prevailing westerly winds that carried the exposed sand and redeposited it along the hills of the old shoreline.
The lake level rose and fell almost constantly in the subsequent centuries and some of the old shorelines are still visible where the level stabilized for a longer period of time. The map above shows the location of some ancient shorelines that appear in the natural area: Lake Algonquian Beach (10,000 B.C.), Upper Group Beach (8,000 B.C.), Lake Nipissing 1 Beach (2,500 B.C.), Lake Nipissing 2 Beach (2,000 B.C.) and Lake Algoma Beach (800 A.D.).
I also found a dandy description with diagrams at the Geography Department at Michigan State University. If you’ve read this far, you’ll really like that.