Elidir Fawr

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Elidir Fawr
Elidir Fawr from Mynydd Perfedd
Range: Snowdonia
Summit: 3,031 feet SH612613
53°7’51"N, 4°4’34"W

Elidir Fawr is a mountain in Snowdonia, in Caernarfonshire, the northernmost peak in the Glyderau.

To the north of the summit is a small lake, Marchlyn Mawr, which is the upper reservoir for Dinorwig power station, a pump-storage power station hidden inside the mountain. Water from this lake flows through huge tunnels into the lower reservoir Llyn Peris. From the north, Elidir Fawr is very prominent, and can appear to be higher than the higher mountains behind it.

Much of Elidir Fawr is known as "the electric mountain", as the Dinorwic Power Station sits on and within the mountain.

Dinorwic Power Station

Deep within the mountain is the remarkable Dinorwic Power Station, built in the abandoned Dinorwic slate quarry. It is not a conventional power station in that it does not generate net power output but it is an important station for regulating power use in the National Grid.

During times of low demand, water is pumped up into the Marchlyn Mawr reservoir on the mountain using the unused capacity of the grid. At peak time the water is released and rushes down through turbines to generate electricity and down into Llyn Peris below; thus Dinorwic actually takes more electricity than it generates but it provides power when it is needed. The station operates now mainly as a "peaking station".

12,000,000 tons of rock had to be moved from inside the mountain, creating tunnels wide enough for two lorries to pass comfortably, and an enormous cavern 167 feet high, 600 feet long, and 75 feet wide known as "the concert hall". This has also given rise to the station's alternative name of "Electric Mountain".

Dinorwic Quarries

From Llanberis, the mountain is dominated by the former Dinorwic slate quarries and the waste they have left behind.

In the heyday of the quarries, the dslates were carried down to the sea on a narrow gauge railyway to be shipped from a harbour developed by the quarry company, which thus gave a name to the village of Port Dinorwic.


Elidir Fawr from Moel Eilio, with the Dinorwic Quarry

It is a reasonably short, but steep walk up to the summit, and this can be undertaken from the Deiniolen side or from Nant Peris. The Deiniolen walk provides views down to Llanberis, while the Nant Peris approach is short and quite steep.[1] The summit can also be reached from Ogwen Cottage via a traverse of Y Garn and Foel-goch. The route makes its way around the headwall of Cwm Dudodyn to Bwlch y Brecan and up to the rocky summit of Elidir Fawr.


  1. Nuttall, John & Anne (1999). The Mountains of England & Wales - Volume 1: Wales (2nd edition ed.). Milnthorpe: Cicerone. ISBN 1-85284-304-7.

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