July 06, 2011
Photographer: Stan Celestian; Stan's website
Summary Author: Stan Celestian
The photo above, taken on the shores of Lake Ontario near Oswego, New York, shows an example of a type of glacial till known as gumbotil. This glacial gumbo is a type of ground moraine that was deposited by the Pleistocene continental glacier that moved south from its center over what is now Hudson Bay in Canada. As the glacier moved to the south it scoured out the Great Lakes. The enormous amount of sediment it generated was plastered onto the ground, beneath the glacier, to create this deposit. Note that the large piece of limestone below the lens cap has many crisscrossing striations that were caused by its abrasion while being pushed against other rocks as it was moved along by the glacier. The glacial gumbo is a dark colored weathered deposit that is very sticky when wet and very hard when dry. As you can see by the image on the right, it’s very poorly sorted and rich in clay. Locally it’s also known as hardpan. Image taken June 2011.