Over the last one million years, there have been a dozen or so ice ages that have helped change the landscape of North America. The greatest of these occurred around 650,000 years ago and resulted in a period of extreme ice buildup that advanced well into the American Midwest and southern Germany.
With each ice age, there are changes to the landscape as the ice carves out new valleys, rivers and streams when they advance and recede.
The last glacier to cover North America was known as the Wisconsin Glacial Episode, which contained the Cordilleran Ice Sheet, the Innuitian ice sheet and the massive Laurentide ice sheet, which was the ice sheet to cover southern Canada and the USA.
It was the Laurentide ice sheet that moved across this quarry and contributed to the erosion of the bedrock you see at the posted coordinates and the reference point.
Laurentide ice sheet
Types of glaciers
There are two primary types of glaciers:
Continental: Ice sheets are dome-shaped glaciers that flow away from a central region and are largely unaffected by underlying topography (e.g., Greenland and Antarctic ice sheets);
Alpine or valley: glaciers in mountains that flow down valleys. When two or glaciers meet and merge at the base of mountains, the new glacier is called a piedmont glacier. If the piedmont glacier flows to the sea, it's called a tidewater glacier.
1) cirque glacier - glacier confined by a valley; forms in a cirque (semicircular basin at head of valley formed by plucking of bedrock by glacier moving down hill).
2) valley glacier - form in a valley.
3) ice caps - cover mountain tops.
Flow of glaciers
Near the top of the glacier, the ice can fracture due to stresses associated with flow. These fractures are called crevasses. In the lower parts of the glacier, the ice flows like a fluid; this region is called the zone of plastic flow. At the very base of the glacier, the ice slips over the surface (a process called basal slip). Typical flow speeds for glaciers are a few mm to a couple meters per day. However, occasionally glacial surges occur; during these times, glaciers can move up 6 km/year. Many crevasses form during glacial surges.
Glacial erosion
Glacial grooves and striations are gouged or scratched into bedrock as the glacier moves downstream. Boulders and course gravel get trapped under the glacial ice, and abrade the land as the glacier pushes and pulls them along.
Glacial Abrasion occurs when rock and debris, also referred to as clasts, are picked up by an advancing glacier and moved along at the base of the glacier over the bedrock where it scours and scrapes the land and soil below, similar to the effect of sandpaper on wood. Deep, long marks or scars appear on the surface of the bedrock below, running in straight, parallel lines indicating the direction the glacier was moving
Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size
Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier". As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. The freezing and thawing action of the ice enlarges, widens, or causes further cracks in the bedrock as it changes volume across the ice/water phase transition (a form of hydraulic wedging), gradually loosening the rock between the joints. This produces large pieces of rock called joint blocks. Eventually these joint blocks come loose and become trapped in the glacier.
Roche moutonnée (or sheepback) is a rock formation created by the passing of a glacier. The passage of glacier ice over underlying bedrock often results in asymmetric erosional forms as a result of abrasion on the "stoss" (upstream) side of the rock and plucking on the "lee" (downstream) side. These erosional features are seen on scales of less than a metre to several hundred metres
Whaleback: similar to a roche moutonnée, but on a larger scale. Whalebacks are streamlined on all sides(including the up-and down-ice ends. They are formed beneath relatively thick, slow, warm-based ice with little meltwater and no basal cavities.
Logging requirements
To log this earthcache you need to answer the following questions and send the answers to my profile. Please include the names and number of people in your geocaching group. Once the answers have been submitted by your group, you are free to post your found log.
Logs submitted without answers within 5 days risk being deleted. If you are travelling, please indicate that in your log and when you plan to submit the answers.
- Based on the types of glacial erosion listed on the cache page and your observations at this site, what type of erosion do you see if. Please list all types of erosion if you note more than one type.
- Does the erosion indicate the direction that the glacier was travelling. If yes, indicate this direction, (Example N, NE, E, SE, S, SW, W, or NW)
- At the reference point located on the north rim of the quarry, is the erosion the same or different. What differences and similarities can you see? Is there a direction to the erosion at this site and if so, is it the same as at the posted coordinates.
References
http://www.ux1.eiu.edu/~cfjps/1300/glaciers.html
http://www.ontariowildflower.com/andy_fyon_mndm_ogs_friends_of_misery_bay_aug1412_final2.pdf
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