Rock Trails Snowdonia Bonus Walk 14

SnowdoniaPaul Gannon

a hillwalker’s guide to the geology & scenery

14Crimpiau & Creigiau Gleision Bonus Walk

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Crimpiau & Creigiau Gleision

Pen Llithrigy Wrach

CreigiauGleision

Craiglwyd

CraigWen

Crimpiau

Cefin yCapel

CapelCurig

To Betws y Coed

Y Pincin (The Pinnacles)

Leat

LeatLL

YN COWLY

D

Llyn Crafnant

Llyn Coryn

14Crimpiau & 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 • • • • •

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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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.

Photo w14.1 Cross the stile and follow the muddy track up the

slope - dolerite lower right, tuffs to upper centre and right.


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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 erup-

tions, 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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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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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.

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.

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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 dol-

erite. 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.

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.


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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.

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.

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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 doler-

ite 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 increas-

ingly 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.

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.


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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

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.

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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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Rock Trails Snowdonia Bonus Walk 14