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Welcome To The Blue Creek Conservation Area's Glacial Grooves
Kelley's Island in Lake Erie is well-known for possibly having the most amazing set of glacial striations and grooves on the planet (see related webpage for more info). However, not many have known that Lucas County Ohio, and the Toledo Metroparks, have a set of glacial grooves themselves. The opening of the Blue Creek Conservation Area Metropark has granted us access to these geological remnants of the glacial age.
Glacial Grooves are formed through a process known as glacial abrasion where scratches are observed which cut into the bedrock. These grooves or striations are further seen as multiple parallel grooves which represent the movement of sediment loaded base of the glacier. They further have been said to have formed by the dragging of coarse gravel and boulders underneath the glacier which results in the cutting of the grooves. Finer sediments and particles also move at the base which causes the glacier to scratch the bedrock, thus forming grooves. Researchers have also found that these glacial grooves were exposed during the Last Glacial Maximum (when ice sheets were at their maximum extension, between 26,500 and 19,000–20,000 years ago). As a result, these glacial grooves and striations provide evidence to the flow of glacial ice and extent of weathering which may have occurred.
When a rock shows scratches or lines on the surface as a result of glacial erosion, it is classified as having striae. Striae are formed when a glacier containing clasts embedded at the bottom of the ice passes directly over a rock, abrading the surface as it moves.
How these clasts carve the ice is categorized by three different types:
•Type 1: Through pressure, the embedded clast abrades the surface of the rock becoming wider and deeper as it moves down the rock. The striations cease only when the clast is released due to pressure or force on the clast.
•Type 2: This type is classified by a slowly rotating clast which increasingly causes deep gouges until it reaches the midpoint, in which the clast rotates at a higher page until the clast has the same velocity of the ice, causing the striations to be less deep, and smaller in size. The deep gauges leading to the midpoint are a result of a large ploughing angle, however this angle decreases as the glacier passes over the rock.
•Type 3: Formed when a clast initially comes into contact with the rock surface, and as the clast rotates down ice, it become displaced and the ploughing angle decreases. This causes the striations to decrease in size as the glacier continues to move.
The formation of striae are commonly used to determine previous ice movement direction, since it is believed that the striae are parallel to direction of ice flow. The thickness of the striae may also determine the age of advancement, with thicker lines being older, and finer striations showing a younger age. Finer striae are assumed to be a younger age since it would be destroyed by thicker striae if abrasion occurred earlier.
To complete this earthcache::
1. (A compass would be handy) Knowing glaciers moved in generally from the North, calculate the direction of the glacial flow over this area. Establish which direction from the glacial grooves is due North, note the parallel striations, and determine the direction from the North. You may record your find in either degrees or general directions.
(for example: the glaciers moved 230 degrees from the North, or moving to the West-South-West)
2. Determine which of the three types of striations these grooves are, using this guide:
•Type 1: This type resembles deep gauges in the rock as the striae become wider and deeper as the glacier continues to advance.
•Type 2: This type has a centre point in which the highest width and depth occurs, with thin, indistinct lines that widen and decrease leading to and away from the median.
•Type 3: This type consists of deep gouges that are initially at its widest, and become narrower and less deep as the glacier moves down the rock.
3. Are these striations newer or older grooves?
4. Send your answers as an email to the cache owners via link at top of cache page.
5. (perfectly optional) Post pics of your visit to this great, new, open-to-the-public, area.
References:Iverson, NR. 1991. Morphology of glacial striae: implications for abrasion of glacier beds and fault surfaces. Geological Society of America Bulletin, 103, 1308-16
Glasser, N.F., & Bennett, M.R. 2004. Glacial erosional landforms: origins and significance for palaeoglaciology. Progress in Phsycial Geography. 28 (1), 43-75.
Goldthwait, R.P. 1978. Giant Grooves Made by Concentrated Basal Ice Streams: Processdings of a Symposium held at Carleton University. Journal of Glaciology, Vol. 23 (89), 297-307.