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Cwm Llydaw and the Summit
The view on the slide looks across the Glaslyn valley towards Snowdon,
which is visible in the background. The Bwlchysaethau arete is on the
left. Over the rock lip in the centre of the picture is Cwm Llydaw.
and beyond the higher shoulders lies Cwm Glaslyn. Both these ice-scoured
hollows have lakes which are fed by many small streams running down
the N.E. slopes of Snowdon. From Llyn Glaslyn at 2,200 feet, the waters
flow over two great steps and eventually pass through a gorge cut in
the rock barrier to tumble down precipitous slopes into Llyn Llydaw
at 1,400 feet. The waters then fall over the lip visible in this view
to the Glaslyn valley below at 500 feet. This last fall has been used
to produce hydro-electric power since 1906. The penstocks, which lead
the water down onto the turbines in the power station, can also be seen.
The slope in the foreground, like most of Snowdon, is covered by fescue
and bent grass. Most of the slopes are too steep and well drained for
bog to develop, and only on the flatter floors of the cwms are there
Nadus and Molinia grasses and peat bog. There is very little heather
in Snowdonia as the sheep tend to graze it out.
Llyn Llydaw
Llyn Llydaw fills a deep rock basin over a mile long, although on the
slide it is much foreshort-ened. Under the precipices at the head of
the lake on the right it is overdeepened to 190 feet. Here, the scree-covered
slopes which fall to the edge are young and not yet colonised by grass
(still subject to active erosion ?). Streams flowing down the rock face
bring silt which is gradually filling the lake. Off the picture to the
right is Llyn Glaslyn, 600 feet higher and 127 feet deep. To the left
is very fresh looking moraine at the outlet of the lake. The tumbled
mass of glacier-broken stone and rock powder marks the end of the Llydaw
glacier as it melted. The morainic deposits have made the lake shallow
at this end, at one time blocking and holding the water at a higher
level. The overflow has since cut down through the moraine to the bed
rock and it is now cutting into the exposed rock lip. The low mounds
in the centre of the picture are part of the lip rising to the left,
which has been rounded and striated by the ice.
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