If you walk the coulees, you'll be quite familiar with all the short tributaries that feed into the main river valley. What you may not have noticed is the direction that many of the tributaries take. Nearly all tributaries on the Old Man River between Pincher Station and Lethbridge are aligned NNE, approximately 70 degrees, regardless of the angle of the valley and main riverbed.
It is known that the coulees were originally formed by the final glaciation of the Pleistocene, known as the Wisconsin glaciation. When the glaciers of the Wisconsin retreated, large amounts of water flooded the Alberta landscape. These meltwaters forged the dry valleys that lead into the Oldman River. Southern Albertan's, among other people, call these dry valleys coulees. Geomorphologists have began to think the coulees we see today aren't entirely the product of the Wisconsin glaciation.
C. Beaty in the Landscapes of Southern Alberta notes that coulees from Lethbridge to the Rocky Mountains are roughly parallel to the wind. These include the coulees of the Oldman River, Castle River, Belly River amongst other rivers in this south western region. According to Beaty, as seen from low flying aerial photos, this is an alignment with the south westerly prevailing wind of this region. This theory is know as coulee alignment. Some geomorphologists refute coulee alignment, they say that sand blasting is observed more on the interfluves where they face west instead of within the coulees.
Another theory to the origins of the modern coulee (E. A. Babcock, 1974) is that coulees orientation is largely a product of structural features of bedrock below the surface, mainly joints and faults. According to Beaty, while this theory may be true for some surface features, it is quite inadequate for coulee alignment. R.J Rogerson, (personal communication, 2000) feels that structural joints resulting from the westward movement of the North American Plate are important in controlling orientation, as found elsewhere particularily in the Great Plains of the United States.
References:
Babcock, E.A. (1974) Photolineaments and regional joints: linament density and terrain parameters, south-central Alberta, Bulletin of Canadian Petroleum Geology 22, 89-105.
Beaty, C.B. (1975) Coulee alignment and the wind in southern Alberta, Canada, Geological Society of America Bulletin 86, 119-128.
To log this earthcache, you must send me answers to the following questions. If you do not answer the questions within an reasonable amount of time, your log will be deleted.
1. Starting from where you should be standing, how may rows of hill extend down from below you toward the river and what direction do they point?
2. Approximately how far from the river are you?
3. If you are facing south, what to your immdiate left is the major erosion feature? (Be VERY careful if you walk over to check!)