Rock Trails Snowdonia Bonus Walk 14

Crimpiau & Creigiau Gleision Bonus Walk

Snowdonia Paul Gannon

a hillwalker’s guide to the geology & scenery

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Crimpiau & Creigiau Gleision

LY D

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LL YN

CO

W

Pen Llithrig y Wrach

Leat Creigiau Gleision

Craiglwyd Llyn Crafnant Leat Craig Wen

Crimpiau

Llyn Coryn

Cefin y Capel

Y Pincin (The Pinnacles)

Capel Curig

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To Betws y Coed

Crimpiau & Creigiau Gleision

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Walk #14 Crimpiau & Creigiau Gleision Start

Bus stop & car parking at Capel Curig (720 581)

Finish

Circular route

Time

5 hours plus

Grade

Navigation

Terrain severity

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Creigiau Gleision is one of those mountains that walkers tend to overlook. Especially when seen from the A5 road between Capel Curig and Llyn Ogwen, it appears to be a wholly unremarkable crest of rock atop a very tedious-looking boggy, grassy slope.

Indeed, it is hardly noticeable at all given the wealth of ‘look-at-me peaks’ that cluster around the road near Llyn Ogwen.

However, for those who climb its flanks, Creigiau Gleision offers superb views and excellent walking (if you discount the boggy bits). The geological features are not so immediately obvious as the wonderful views. But, once alerted to some basic details, the geology too should leave a deep mark on your impressions of this mountain.

This is a potentially difficult area for navigation, with innumerable humps and dips, many looking very much the same as each other and it can be hard to match what you see on the ground to the map. However, in clear weather this should not be a problem – though unless you are already familiar with the area it is best avoided in the mist. The terrain is often wet or boggy and involves a lot of walking up and down over the knolls and dips. That said, this is a fine walk and you should not be put off by these concerns – good boots (and gaiters if you have them) will get you across the wet parts and careful use of an Ordnance Survey map (preferably the 1:25,000 OL 17 map), combined with a compass and these instructions, should get you round the route. Beware that some of the terrain to the west of Creigiau Gleision, as far as the

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Crimpiau & Creigiau Gleision

Photo w14.1 Cross the stile and follow the muddy track up the slope - dolerite lower right, tuffs to upper centre and right.

main road, is horrendous, so it is important to take care to keep on the footpaths at the end of the walk.

Under no circumstances should you venture around here without an OS (or Harvey) map. The sketch map provided with this walk is not sufficient for use to guide you round the complexities of the terrain and is only intended to allow you to work out the route on the OS map. Also, in the event of an accident, you may find it difficult to get a mobile phone signal in some places, so always take a whistle as a back up (six long blasts every minute is the recognised distress call).

Much of Snowdonia is made up of very tough volcanic rock that was erupted over 400 million years ago. These rocks have been carved, by aeons of years of erosion by water and ice, into the present day landscape. On this walk we will get the chance to see two of the most common of the Snowdonia volcanic rocks, tuffs and dolerites.

There are several other rock types passed on the walk, but to keep matters as simple as possible I will mention only these two (with only a fleeting mention of an area of non-volcanic ‘sedimentary rock‘). In this article, as in the book Rock Trails Snowdonia, I concentrate on what you can see as you walk, without the need for the use of a hand lens.

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Start from Capel Curig, crossing into a field next to an old chapel, following the track up until you pass through a metal gate and immediately after it, turn left up the slope, between a tree and a cluster of boulders. Very soon a stone wall and a stile will come into view up ahead. Cross the stile and turn right, following the stone wall up the hillside as it twists and turns, passing another stile, then approaching two more stiles, higher up. This is a steep section of walk, but gets you high up very quickly and soon levels out. Cross the second of these two stiles (at about 727 583) and carry on along the edge of rocky outcrop on the right to another stile, at about 728 584.

Re-cross the fence at the stile and follow the obvious track up a slight dip between outcrops of rock. The outcrop to the right, at the bottom of the slope, is one of the main rock types that we will see again and again on the walk, known as ‘dolerite’, while those to the left and higher up on the right are ‘tuffs’. When you get to the top of the rise it’s worth a short diversion to the right to the top of the outcrop to appreciate the view back towards Llynau Mymbyr and Snowdon (Yr Wyddfa). If it’s not too windy, this is also a good place to ponder the origins of volcanic rocks (see photos w14.1 & w14.2).

Tuffs are produced by ‘pyroclastic’ eruptions. In Snowdonia there were many such eruptions, caused by the collision of ‘tectonic plates’. The cycle of eruptions which produced the rocks of Snowdon, as well as those of the Glyderau and the Carneddau, took place mainly under sea level, through ‘fissure vents’ rather than through classic ‘cone’ volcanoes.

Photo w14.2 View towards Llynau Mymbyr and Snowdon (Yr Wyddfa).

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Crimpiau & Creigiau Gleision The whole affair was driven by a melting of part of the earth’s mantle, creating molten ‘magma’. This rose up through faults and cracks – the ‘fissure vents’ – in the earth’s crust towards the surface. Tuffs are generally produced by magma that is fairly viscous, so it tends to cool down and block the vents. Pressure of more molten magma rising from below keeps on building up, until eventually the gases confined in the magma eventually become too great, blasting away in an extremely violent eruption of molten fragments and gases. The fragments settle and harden, over time, into rocks such as tuffs.

Dolerite, on the other hand, is a somewhat calmer affair. After the massive pyroclastic eruptions, most of the magma had been erupted, but some still existed, rising up through vents, but not making it all the way to the surface. Instead it was ‘intruded’ between the still soft deposits of the pyroclastic eruptions and was much later exposed to our gaze at the surface by those aeons of erosion. Essentially, all the way to the summit of Creigiau Gleision, our route follows the boundary between the tuffs and the dolerite.

Dolerite is very easy to recognise once you have learned to spot the main characteristics.

It often has a pitted surface (sometimes looking a bit like an extremely bad plastering job), with what appear to be irregular cracks (or ‘joints’) and rounded edges. Tuffs are much more varied, but tend to be quite light coloured, with some pinkish patches, and with more varied ways of peeling apart and often with sharper edges. As you follow the described route, keep on studying the rocks on either side until you feel confident that you can spot a tuff or a dolerite with reasonable certainty.

Return to the track and follow it farther alongside a fence, crossing the fence at a stile at about 730 586, then continue alongside the fence, but on its right-hand side, with tuffs on either side of you.

After a couple of hundred metres the fence does a 90˚ left-hand bend. Our route also bears left, just a short distance beyond the corner of the fence, on a muddy track which takes you along the right-hand side of the dip and away from the fence. The track here can be very wet indeed.

Note the cliffs on the left-hand side of the dip. These are outcrops of tuffs, while the dolerite on your right forms more rounded crags. As you go farther along the muddy track you’ll start to see a small lake nestled under the cliffs, Llyn y Coryn. Shortly after this you should encounter three lumps of quartz – a bright white rock – embedded in the track. These indicate that you need to bear right here, to follow a minor track up between crags rising to the summit of Crimpiau (see photo w14.3).

The outcrops on the right as you ascend are dolerite, while the less prominent outcrops on the left are more examples of tuffs. Farther up, the dolerite seems to take over completely,

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Photo w14.3

On meeting these lumps of quartz, bear right on small muddy track to the right, rising between the outcrops of tuffs upper left and of dolerite upper right.

Photo w14.4

View of Creigiau Gleision from the summit of Crimpiau – a much more impressive view than from the A5.

coming right to the edge of the ridge. A short distance farther on, the situation is reversed and the tuffs start to reappear, eventually pushing the dolerite off to the right. The tuffs now become the highest outcrops. Look out for, and follow, the small track that bears off left to cross the top of the tuffs, while the main track sticks with the slight dip separating the dolerite and the tuffs.

Eventually you reach the summit of Crimpiau and its excellent views. From here the craggy south-east flank of Creigiau Gleision is highly impressive – so completely different from the view from the A5 (see photo w14.4). Descend to the bwlch (col) and head towards Craig Wen, crossing the tumbledown stone walls as necessary. As you get close to Craig Wen, it’s worth studying the scenery around you. Indeed the bwlch and its stone walls make a good place to sit down, especially if the tops are windy.

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Crimpiau & Creigiau Gleision

Photo w14.5 A view from the bwlch between Crimpiau and Craig Wen towards Tryfan and Llyn Ogwen. The low land immediately below is mainly ‘sedimentary’ rock interspersed with tougher bands of the volcanic rock making up the hummocky outcrops.

The low area to the south-west is largely made up of much softer ‘sedimentary’ rocks rather than the tougher volcanic rocks which make up the higher ground (see photo w14.5).

Sedimentary rocks are formed when particles of rock are eroded from mountains, carried down by streams to be dumped in a lake or sea, there accumulating and eventually hardening into solid rock. Generally sedimentary rocks are softer and more easily eroded than volcanic rocks and this relative strength accounts for many of the differences in relief in Snowdonia.

Also look up towards Craig Wen (see photo w14.6). The main crags are made up of dolerite. But the minor crags on the left are tuffs. The route from here to the summit of Creigiau Gleision follows the dip between the tuffs and the dolerite. There are also some flat sections to be crossed, which can get very boggy. The route rises in several sections of steepish climb followed by flatter boggy areas. As you get higher the tuffs become less and less obvious, but the dolerite forms high crags on your right all the way, except through the boggy areas. If you want – and have the energy – you can scramble up and follow the top of the dolerite crags, but it involves redescending with care at the end of each crag.

As you near the summit of Creigiau Gleision the best route is to bear off right and scramble up on the ridge as soon as practicable (see photo w14.7). Alternatively follow the main track – but keep an eye out to the right as it’s easy to pass the summit cairn without noticing it.

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Photo w14.6

Craig Wen, with dolerite forming the high point upper centre of the picture, and tuffs to the left. The track rises between the outcrops but is not visible in the photo.

Photo w14.7

An outcrop of dolerite on the summit ridge of Creigiau Gleision. It is possible to scramble (with care) up to the summit ridge on the left of this outcrop.

The summit views are excellent with the great mountains of the Carneddau – especially Pen Llithrig y Wrach (‘the hill of the slippery witch’) – and the Glyderau dominating the outlook to the north and west. But to the south and east, the hills roll gently off, with range after range of upland disappearing in the distance. This is open country par excellence and is guaranteed to set you thinking about exploring these delightful looking ridges and hills.

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Crimpiau & Creigiau Gleision

Photo w14.8 The bands of tuffs and dolerites crossed while walking along the summit of Cregiau Glesion are here seen as dipping steeply from upper right to lower left.

From the summit onwards the pattern of the rocks changes. Instead of walking along a boundary between the tuffs and dolerites, the route crosses one band after another of dolerite and tuffs – see if you can spot when the changes occur (also watch out for a prominent band of white quartz later on).

The walk along the summit ridge is superb, but can be very windy at times. I was once pinned down by a fierce wind, near the slight col where the band of quartz crosses the track, and it seemed like several minutes before I could make progress and get out of the wind behind the next slight rise.

The track eventually takes you to a fence at about 736 623. Cross the fence and bear left heading down to the dam across Llyn Cowlyd’s north-eastern end. Muddy and slippery at times, with the track being easy to lose lower down, care needs to be taken on this fairly tough descent, but soon you reach the lake and magnificent views along its length.

There is a nice narrow track on the south-eastern shore, but for our purposes it’s best to follow the track on the north-western side. As you progress along this track you get increasingly impressive views of Creigiau Gleision’s rock wall. You can clearly see the bands of dolerite and tuffs that you crossed on the summit ridge, dipping down from upper right to lower left (see photo w14.8). These beds were originally laid down horizontally, one on top of the other, but have been pushed up to this steep angle by a later phase in the collision of the tectonic plates, some time after the end of the volcanic cycle, and here form one side of an anticline.

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Photo w14.9 Looking back down along Llyn Cowlyd. Although the lake is a reservoir, this valley is a classic glacial outflow channel. A glacier of ice being pushed out from an ice sheet in the Migneint smashed through the rocks to carve out this valley. The reservoir is served by two leats that drain the western slopes of the Carneddau.

The reason that you can see all this is because during the ice age a glacier smashed through the rock at the far end of the lake and carved out this valley. The last of the ice melted only about 10,000 years ago, a mere tiny morsel of time in geological perspective, but bringing us right up to the time when people began to move into the area and to play a part in shaping its landscape.

Llyn Cowlyd is actually a reservoir, feeding a hydro-electric power station in the Conwy valley (see photo w14.9). When you get to the far end of the lake you’ll see a surprisingly large stream pouring down from the bwlch or col. When you reach the bwlch itself you’ll see why; two leats feed water collected from the western flank of the Carneddau into the reservoir in an impressive feat of engineering.

The best way to return to Capel Curig is to head WSW to Helyg (at about 691 602), cross the road and river and then follow the old road in the shade of Gallt yr Ogof and Cefn y Capel.

The views back across to Creigiau Gleision and Crimpiau are excellent and will be seen in 11

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Crimpiau & Creigiau Gleision completely different light now that you have seen the summits of these minor mountains.

A shorter route is to follow the (boggy) bridleway to near Bron Heulog (at about 719 589), then follow the main road. But, be warned, the pavement is unusably narrow indeed in places (and only just about wide enough for a slim person at others) and traffic moves very fast and close to the edge of the road around the bends near Capel Curig. Walking along here can be extremely unpleasant and is potentially dangerous. So for a less stressful end to the day’s walking I recommend going for the longer option (and it has much better views anyway).

Cover Photo Creigiau Gleision view.

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