Isle of Mull: Carsaig Arches
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The Carsaig Arches lie on the southern edge of the Ross of Mull, 30km (18 miles) by crow, south-west from Craignure. The village of Carsaig, where the approach begins, lies down a narrow forested road running south from Pennyghael.
South Mull Coast Site of Special Scientific Interest (SSSI) comprises a 17km coastal strip centred on Carsaig Bay. The site is of multiple geological interest comprising volcanic (igneous) rocks and sedimentary rocks of national importance.
The sedimentary sequence illustrates the change in environmental conditions in the area, from marine deposited sediments to the rarest and most significant sediments, the Tertiary sandstones and mudstones. The Tertiary sediments are sandwiched between the Cretaceous marine deposits and the overlying basalt lava, and contain features indicative of a warm and rather arid environment. This environment changed at the start of the Tertiary period as purple mudstone formed through the weathering of volcanic ash under damp conditions.
The dykes and sills at Carsaig are of particular interest. Dykes and sills represent intrusions deep below the Earth’s surface. Dykes cut across features like bedding planes whereas sills tend to flow along planes of weakness in the rock.
The main Carsaig Arch is a magnificent freak of Nature, a huge tower, with a large hole, not unlike a giant keyhole, through its middle. The base of the rock is Cretaceous, i.e. the period of geological time 145-65 million years BP, during which the dinosaurs became extinct, while the upper part of the rock is basalt.
To claim this cache
(a) email the owner with your estimate of the height of the main tower at Carsaig;
(b) The volcanic activity marked by the purple mudstone, caused the eruption of layer upon layer of lava forming the ‘plateau group’ of basalts now weathered to form a step-terraced topography characteristic of Mull. What type of rock do you find embedded between the lava flows, and how do you think it was formed?
(c) this rock, sandwiched between the lava flows, is of a particular type; if you gently run your fingers across it, what does it feel like, what is its texture?
(d) estimate the height of the main cliff along this stretch of coastline; and
(e) while this is not a specific requirement, it would be interesting to others if you could upload a photograph of the arch formation.
Getting there It is best to make the walk as low tide is approaching. In some high tide conditions, it may not be possible to approach the final arch.
PLEASE NOTE: The final section of this walk has become increasingly eroded and unsafe. Do not go further than you feel competent to do. If you cannot complete the answers to my questions without going further, just do the best you can, and send me a picture of yourself at the first arch. That will suffice.
Set off from the pier in Carsaig, and take to the track round the shoreline of Carsaig Bay. You soon encounter a fence, and here it is easier if you descend to walk along the shore; this makes it simpler to cross a couple of burns that lurk a short way ahead. Once beyond this little hiatus and onto the western side of the bay, the path improves and leads on to a feature known as the Nun's Pass or Nun's Cave, the only spot where the cliffs that accompany this walk are even remotely breached. The cave, well worth a brief diversion, is said to be the place where nuns evicted from Iona are said to have taken refuge during the Reformation. The cave, wide and shallow, and formed of sandstone topped with basalt, was formerly used by stonemasons working in a nearby quarry to extract sandstone used on Iona and elsewhere. The quarry remained in use until the late 19th century.
By crow the on-going distance to the Carsaig arches is not significant, but progress is very slow. There has been some damage to the path here, but the ways round it, higher or on the beach, are evident enough. You now press on below the cliffs of Aoineadh Mòr, at times following a grassy sward bright in springtime with flowers; at other times you find yourself among the rocks and pebbles on the beach.
But eventually you round a corner and the first arch rises before you. Cross the beach towards it, and climb onto a basalt outcrop, but only to find that an inlet bars further progress in that direction. To get any further you need to backtrack a little to a small burn and look for a goat track that takes you very precariously above the inlet – no place for any but the sure-footed. So, take no risks.
Further on, the path does come down to the beach to reveal that the second archway, taller and more slender than the first and topped by a chimney-like stack, is linked to the landward cliff by a natural, rocky causeway.
Hopefully you have arrived at low tide and have time to explore. But once you have taken all the pictures you can manage, the safest return is by your outward route.
(No hints available.)