Loch Glencoul
Loch Glencoul is an excellent place to view the effects of thrust faulting during the Caledonian mountain building period. Geologists can categorize faults into three groups based on the sense of slip:
Normal Faults occur when the crust is extended. The hanging wall moves downward, relative to the footwall. A downthrown block between two normal faults dipping towards each other is called a graben. An upthrown block between two normal faults dipping away from each other is called a horst. Low-angle normal faults with regional tectonic significance may be designated detachment faults.
Reverse Faults are the opposite of normal faults. The hanging wall moves up relative to the footwall. Reverse faults indicate shortening of the crust. The dip of a reverse fault is relatively steep, greater than 45°.
Thrust Faults fault have the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and foot wall) folds. Thrust faults form nappes and klippen in the large thrust belts.
Strike-slip Faults: The fault surface is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion.
Loch Glencoul is an excellent place to view the effects of faulting during the Caledonian mountain building period. Older metamorphic rocks have been moved on top of the Cambrian succession on a major fault line, the Glencoul Fault. The metamorphic rock above the Glencoul Fault is Lewisian Gneiss, like the rock found underneath which is Torridonian and Cambrian. The Moine Fault itself, with its overlying Moine Schists, lies at a higher level, appearing at the surface further to the east of Loch Glencoul.
This view towards the north shore of Loch Glencoul shows the Cambrian quartzite crags on the left, the Glencoul Fault above them, and then, occupying the rest of the ridge to the right, Lewisian gneiss that makes up the thick slab of older metamorphic rock above the Glencoul Fault.
This photograph of the south shore of Loch Glencoul looks directly along the outcrop of the Glencoul fault plane. In the centre of the picture a clear straight line separates the rugged Lewisian gneiss outcrops above the fault from the green slopes beneath. The row of dark green bushes is growing on outcrop of the Fucoid Beds.
Sources:
http://www.earth.ox.ac.uk/~oesis/nws/loc-glencoul.html
http://en.wikipedia.org/wiki/Fault_(geology)
Log Requirements:
You may log your find as soon as you have sent the answers to the three following questions via e-mail to thegreentool@gmx.com. Your log may be deleted if you don't do this.
1. Observe the two prominent fault lines above the north shore of Loch Glencoul and identify the type of fault you're looking at.
2. Please estimate the angles of both faults.
3. The information board compares the movement of the rocks with something. What do the moving rocks look like? (It's not "Like a sandwich"!)
Optional: Please add a picture showing you or your GPS in front of the information board. You can add it to the log or attach it to the e-mail.