Landscapes that experience glaciations undergo considerable modification as a result of the erosion caused by the moving of masses of ice.
Direct glacial erosion is accomplished by three processes, abrasion, crushing and plucking.
Roche Moutonnee is a rock formation that was created by the passing of a glacier. The passage of the glacier over existing rock 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 one meter to several hundred meters. The contrasting appearance of the erosional stoss and lee aspects is very defined on roches moutonnees. All the sides and edges have been smoothed and eroded in the direction that the glacier passed over it. It is often marked with glacial striations. The rough and craggy down-ice side is formed by plucking or quarrying, an erosional process started when ice melts slightly by pressure and seeps into crack in the rock. When the water refreezes, the rock becomes attached to the glacier. As the glacier continues its forward progress it subjects the stone to frost shattering, ripping pieces away form the rock formation. Studies show that the plucking of the lee side is a much more significant erosional process that the abrasion of the stoss side. The ice sheet that passed over these rocks was about 1 1/2 kilometers thick. It slid up and over the bedrock south of the boat lauch and dropped off the other side that looks out over towards Willows Beach. The ice formed two lobes at the south end of Vancouver Island. One flowed south towards Seattle and terminated near Tacoma. The other flowed westward and northwestward through Juan de Fuca Strait and ended in a shelf some distance to the west of Vancouver Island.
Grooves found in the bedrock will usually be symmetrical, and striations may be seen on the sides and bottoms of the grooves.
Glacial grooves
Another important but indirect erosion process is meltwater erosion. The production of water through melting of ice that undergoes erosional process like loosening, dissolving, and removing action on debris or rock material in a glacial environment is called a meltwater erosion. Glacial meltwater is a very effective agent of mechanical erosion as well as chemical erosion because of the high water pressure that flows through tunnels in the ice at the end as a meltwater stream. The meltwater inside the glacier may be under hundreds of feet of ice and is under great pressure. The release of this water under high pressure mixed with the sediment carves rock along the way like a saw, and enhances the rate of erosion.
The sides of meltwater grooves or channels will not be symmetrical, lip ledges form where the water level erodes the rock as it moves under the the glacier. As ice melted, water under the glacier creates a channel.
Channel groove
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1) Is the groove at the posted co-ordinates symmetrical or asymmetrical?
2) How deep and wide is this groove?
3) Were you able to find lips / ledges in the groove? If so, please take measurements and send them along with your "yes or no" answer.
4) Which side of the roche moutonnee isthe groove (at posted coordinates) located: the lee side or the stoss side?
5) Do you think this groove was created by direct glacial erosion or indirect meltwatererosion? Use the information you have gathered, and in a few sentences explain why.
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