The geological background of Manitoba has been altered by many major historical events. One event from the not too distance past was the time of the glaciers that scraped and scoured Manitoba, starting from the northern arctic and spreading southward almost to the Gulf of Mexico. These glaciers pushed down dirt, gravel and rocks and spread them out along the way then dropping them as they receded back to the arctic circle.
A second major event occurred immediately after the glaciers and was to some extent a result of the glaciers, or at least their melting, and that was the formation of Lake Agassi. This lake covered a greater portion of the Canadian and American midland prairies, sorting the glacial till by it's wave action.
With time, these two events alternately occurring and working together or on their own have caused the bedrock to be covered with differing layers of dirt, gravel and rocks. Each time there was a cycle, the heavier material was dropped first followed by the lighter material which form strata. The thickness of the strata was dependent on the time that was involved and the forces applied and what may have occurred afterwards. So what was created was differing layers on top of each other maybe with a layer of rock, maybe not; maybe a layer of sand, maybe not; maybe several layers of dirt and clay's, the possible combinations are endless.
As the ice melted and the lakes receded, the water soaked into the ground but, due to the differing strata combinations of the soil, clay, sand, gravel, and rock, some areas were able to soak up more water than others. There was also a difference of elevation of some lands over others as various glaciers scraped away the soil or the lakes washed away the soil. With the exposure of the edges of a soil profile, those layers that held water were able to let the water drain out. This water also carried with it some of the soil and left spaces between the larger soil particles and soil layers. Now that these areas were not as hard packed, they became weaker and as more material was washed out these weak areas slowly worked their way further and further back into their layer. Eventually, the strata on top of this weak layer were too heavy for the loose weaker layer and the strata would collapse on top of each other. If there was water still coming out of the weaker layer, it would act as a lubricant and cause these collapsed layers to slide downhill. This area is called a LANDSLIP.
Naturally occurring landslips along the edges of valleys, gorges and river banks can be seen all over and are a natural process of erosion.
Now that man has come on to the scene, his modifications of the earths crust has caused this erosion to occur more frequently where man has made his changes. One of the major changes man has made is for his transportation systems. It is more efficient for a road or railway to be flat so man cuts his way through hills and across slopes, this action exposes the various strata. Being exposed, the free water in the layers is now allowed to run out and produces landslips. Unfortunately, these landslips also result in the washing away of the underlying packed road or rail bed so that part or all of the road or railway is washed downhill making a driving hazard for man's machinery.
The image of the damaged road is a result of a landslip. Water flowing down and into the ditch has washed away the material along the edge of the road and it has collapsed. It is also possible that there is a higher slope to the right of the road and the water in that slope is making it's way through the gravel under the road, washing out the finer particles to make a weaker layer that has collapsed.
As the road through Riding Mountain National Park was being made, it was inevitable that the road bed would have to be cut through a hill or across a slope and the engineers for the road would have to come up with a solution to the potential for a landslip with destruction of the road. It is in the location for this Earth Cache where these remedial actions have taken place.
In this location, there was a depression that was filled to make the road more level. Further north from this section there is a large hill that the road cuts around and there can still be seen cleared areas through the trees where the old road used to go. This old road section suffered drastically from landslip similar to the photo damage. To alleviate this problem the decision was made to move the road, not fix it. One type of fix is illustrated below where a drainage pipe is positioned to drain the outflow water under the road. There is also a coarser rock layer to allow water to slowly peculate through. To keep the rock clean, a synthetic fibre cloth is laid to maintain a separation of layers. Above all this is made a retaining wall to hold back the road bed and road with some top dressing of soil to encourage plants to grow to help stabilize things and make it more aesthetically pleasing to passers by.
To earn credit for this Earth Cache you must send the answers to these questions to the cache owner through geocaching.com to get the OK to log cache as a find:
-
What type of structure(s) do you see that aim to reduce the chance of a landslip here?
-
What are the height, thickness and composition of the structure(s)?
-
At one point along the centre of the structure there is a treated wooden box, speculate on what it's function might be?
To travel through Riding Mountain National Park, a National Park Pass is not required. If you are planning on stopping in the town-site or at an attraction, a Park Pass is required to be displayed.
Placed with permission of Parks Canada, RMNP VEPDO.