The Mourne Mountains.
If you have walked in the high Mournes you will have seen the impressive Tors, particularly on Slieve Binnion and Slieve Bernagh. Have you ever paused to consider how these dramatic rock formations developed?
North Tor, Slieve Binnion.
This cache may be reached from the trail that passes the Blue Lough and gives access to the caches on Slieve Lamagan and Slieve Binnion. Parking is available at Carrick Little. (N.B.The higher car park had a parking fee of £3 per day when this cache was published).
The Explanation.
The Granite Tors of the high Mournes started to form when magma, which was intruded into the Earth’s crust, cooled to form a batholith. This large mass of igneous rock is also referred to as plutonic rock. The softer rock above the batholith eroded away over time leaving the granite exposed to the elements. While the rock was cooling it contracted causing cracks, or joints. These cracks also occurred when the batholith was exposed and the pressure was released.
The joints were made worse by the process of freeze-thaw weathering. When water in the cracks froze it expanded and this repetitive process caused the joints to widen. This is particularly noticeable when the joints are close together. As the freeze-thaw weathering continues pieces of rock break off and form scree.
The smooth round edges of the Tors resulted from a sloping weathering profile beneath the joints. The abrupt overhangs are caused when harder, less weathered granite is found above the horizontal joint. Similar formations can be found on Dartmoor and may be the origin of the famous statues on Easter Island.
The Cache.
To log a find you must send the answers to the following questions to the CO via the message centre above.
When you are at the posted coordinates please stand facing Ben Crom, with the Blue Lough behind you. You will see the SW aspect of a relatively small rock formation that illustrates the process described above.
- Estimate the height of the rock formation.
- What is a batholith?
- Describe freeze-thaw weathering in your own words.
- How many complete, or almost complete, horizontal joints are in the top half of the formation?
- Are there any vertical joints in the top half of the formation, if so, how many?
- Use your imagination and describe any strange images that you see in the formation, or in the rocks to the right.
- What is a Mo'ai?
- It is not compulsory, but please send, with your answers, a photo of yourself, or your GPS device, with the rock formation in the background.
Please note that any logs containing spoiler photographs will have to be deleted.
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