This is another excerpt from a work in progress on the natural history of Lake Ontario to be published early next year by History Press. For more on the title “A Lake Like No Other" and other lake tales plus a great lake video for winter watching visit my website at susanpgateley.com.
One of the largest collections of drumlins, ice sculpted hills of glacial till, in the world lies between Syracuse and Rochester. They orient roughly north south following the flow of the glacier and have a streamlined elongated appearance with the north ends being steeper and the south ends tapering gradually down. From the air they look a bit like streamlined nacelles or perhaps like a school of swimming fish.
A number of those drumlins meet the lakeshore, and as that shoreline erodes into their ends, it creates a series of distinctive clay bluffs between Oswego and Sodus Bay. Recent studies suggest that our drumlins were created over a relatively brief period of a few hundred years near the end of the ice age. When the glacier began to melt it developed “ice streams”. These were areas of rapid ice movement within the glacier. Melt water at the base of the ice may have lubricated and hastened the speed of these ‘rivers’ of ice. As they passed over deposits of till that had been left by previous glaciers they formed the drumlins. Faster moving ice probably created more elongated stretched out hills.
Along the shore where drumlin ends are being eroded away by run off and wave action, geologists can study the interior structure to get clues about the events of the ice age. Some of the bluffs including Sitts Bluff(see photo above) and Chimney Bluff, both in state parks, show considerable variability in their sand and clay with distinct layers giving a faintly banded look to the bluff face.
Often some of the bluffs show a more sandy upper layer. Here you are most likely to see the holes created by nesting bank swallows and kingfishers where the digging is easier. Sometimes areas made up of thin layers of clay called ‘varves’ may appear, indicating this part of the drumlin was formed under water as a lake bed where silt was deposited during runoff events each year in still waters. At least three different colors of clay were obvious as of this writing in a bluff near my house. Yellow, reddish and ‘blue’ clay were all visible in various parts of the cutaway drumlin ends.
These differences in sediment and layering suggest a complicated process of original deposition. Some observers have interpreted this layering of clay as evidence of more than one glacial advance and retreat across the area. The highly sculptured spires and ridges of Chimney Bluffs State Park by Sodus Bay and Sitts Bluff on the east side of Fair Haven Beach State Park show dramatically the uneven erosion of more resistant veins and layers of clay and more easily eroded sandier sediment.
So rather than a homogenous dump, the drumlins are now thought to have been pre existing forms left by earlier ice ages before the last glacier gave them their current shapes.
Erosion of the bluffs provides much of the sediment that makes up our lake shore beaches. We will explore the relationship between bluff and beach in our next post.