Which Is “Harder” - Water or Rock?
The earth has shivered through several ice ages from over its history. Across most of Canada, the most recent ice age peaked about 25,000 years ago and ended by about 10,000 years ago in southern Ontario. This period of the ice age is called the Wisconsin glaciation.
Glaciers, up to 2 km thick, scraped across bedrock, leaving tell-tale marks of it's passage, including glacial striations and glacial grooves. But, beneath the glacier, at the contact with the rock basement, glacial processes left other marks called sculpted erosional forms, or s-forms for short. S-forms have a variety of distinctive shapes when seen on a rock surface, including sickle- or comma-shaped forms (Photo 1 and 2), mussel-shell-shaped, shallow depressions called Muschelbriiche (Photo 3 and 4), and linear troughs or furrows (barely visible in Photo 5 and 6).
Photo 1: Comma-shaped sculptured erosional form, also known as s-form, that was carved into the limestone bedrock, during the last ice age, by super high pressure water vortexes at the base of the ice sheet. Image: Andy Fyon, Lake Erie limestone shelf, Selkirk Provincial Park, Ontario, September 17, 2022.
Photo 2: Comma-shaped sculptured erosional forms, also known as s-form, that were carved into the limestone bedrock, during the last ice age, by super high pressure water vortexes at the base of the ice sheet. Linear s-form troughs are also visible in the image, attached to the comma s-forms. Image: Andy Fyon, Lake Erie limestone shelf, Selkirk Provincial Park, Ontario, September 17, 2022.
Photo 3: Numerous mussel- or divot-shaped sculptured erosional forms, also known as Muschelbriiche s-forms, were carved into the limestone bedrock, during the last ice age, by super high pressure water vortexes at the base of the ice sheet. Faint linear s-form troughs are also visible in the image. Image: Andy Fyon, Lake Erie limestone shelf, Selkirk Provincial Park, Ontario, September 17, 2022.
Photo 4: Numerous mussel- or divot-shaped sculptured erosional forms known as Muschelbriiche s-forms were carved into the limestone bedrock, during the last ice age, by super high pressure water vortexes at the base of the ice sheet. My finger points to two Muschelbriiche s-forms features. Image: Andy Fyon, Lake Erie limestone shelf, Selkirk Provincial Park, Ontario, September 17, 2022.
Photo 5: Numerous linear trough-shaped sculptured erosional forms, also known as s-forms, were carved into the limestone bedrock, during the last ice age, by super high pressure water vortexes at the base of the ice sheet. Image: Andy Fyon, Lake Erie limestone shelf, Selkirk Provincial Park, Ontario, September 17, 2022.
Photo 6: Numerous linear trough-shaped sculptured erosional forms, also known as s-forms, are spatially associated with mussel- or divot-shaped sculptured Muschelbriiche erosional s-forms. The s-forms were carved into the limestone bedrock, during the last ice age, by super high pressure water vortexes at the base of the ice sheet. Image: Andy Fyon, Lake Erie limestone shelf, Selkirk Provincial Park, Ontario, September 17, 2022.
How were s-forms created? Research in the Georgian Bay area of Ontario by the late Phil Kor concluded that these types of erosional s-forms were likely created by super high pressure water vortexes at the interface between the bottom of the glacier and top of the bedrock. This water is called subglacial meltwater.
These and other erosional s-forms, along with glacial striations, are preserved on the flat, limestone bedrock shelf exposure along Lake Erie shore at Selkirk Provincial Park. The features help geologists understand some of the processes that took place beneath a 1 - 2 kilometer thick ice sheet.
Imagine that! Not only did glaciers shape the land by abrading away rock, but beneath the glacier, high pressure water vortexes carved distinctive erosional s-forms into the rock.
Next time you stand on an exposed bedrock area, look down at the rock to see if any erosional s-form sculptures are preserved. That is the first step in gaining a deeper understanding of the geological forces, like glaciation, that shaped the surface of the Earth where we live.
Nov. 8/22; Facebook post: September 24/22