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The southern lakes of Windermere and Coniston

The southern lakes of Windermere and Coniston, set in what the eighteenth century topographers referred to as 'the humble hills', are typical finger lakes.windermere Spa Hotel Windermere, for example, is almost ten miles in length but seldom more than half a mile wide. Partly because of their restricted width, glacial erosion concen¬trated on downcutting with the result that the lakes are surprisingly deep, Coniston going down to 184 ft and Windermere to 219 ft, Their great length also allows the wind to pile up the waters, especially at the northern end. At Coniston the lake level can vary by as much as six feet, and five feet waves are generated when the wind is blowing strongly from the south or southwest.

Ponding up of water at the northern end of the lake due to strong winds is also apparent on Windermere. The lake level also responds to the flood water brought down by the River Brathay. Debris brought down by the river has led to the building of a small lake delta near the site of the Roman fort of Galava , but due to the relatively deep water hereabouts it is only being extended slowly into the lake. Deposition in the past has led to the creation of extensive lake flats at the head of Windermere, but certainly during the past two thousand years their formation has been a very slow process. The remains of a stone jetty built by the Romans to serve their fort is still near the present low water line, but owing to the compaction of the soft lake sediments it is now largely submerged. The sediment of the lake bed consists mainly of fine mud in the deeper basins and multicolored clays in the shallow parts. Some of these clays have a distinc¬tive layered appearance , each layer representing an annual accumula¬tion of sediment. From these varve layers and the nature of the lake deposits, Dr Pennington has worked out a postglacial time scale for the Windermere area and thrown considerable light on the events which followed the retreat of the ice.

The mountain tops and upland slopes, no less than the glaciated valleys and lake basins, show clear evidence of being molded and modified by ice action in the past. One of the surest indications that ice once overrode even the highest parts is the presence of erratic's, that is, rock fragments carried some distance from their source outcrop. Where these have a distinctive appearance and therefore are easily identifiable in hand specimens, they can be of great value in tracing former ice movements. Not all the rocks which litter mountain tops like Great Gable and Scafell are 'foreign' erratics. Many have been formed in situ by intense frost shattering when the peaks stood out above the blanket of snow and ice on the lower slopes.

This special type of process termed per glaciation has left its mark in the great boulder fields and elongated strips of shattered rock on mountain tops like Saddleback  and Grasmoor. Although per glaciation reached its climax during the Ice Age and shortly after, it can still occur today. Towards the edge of the flat summit of Grasmoor, for example, at a height of about 2500 feet, winter frosts not only shatter the slates but also sort out the resulting fragments into a linear pattern resembling the furrows of a ploughed field. The coarser stones tend to lie on the ridge tops while the smaller fines accumulate in the intervening hollows.

The sorting of the stones in this way is a complex process involving heaving of rock fragments of the surface layer when it is subject to alternate freezing and thawing. There is also a mass movement of debris downhill under gravity and this contributes to the linear appearance of the surface. At the present time, the effects of per glaciation are best seen after a severe winter of intense night frosts. By the summer the surface may have lost its distinctive patterning. A similar 'micro' form is the stone poly¬gon which consists of a rough circle of broken angular stones often projecting through a thin turf or moss covering. These, too, are formed by frost action and can be seen at a number of places on the plateau summit of Grasmoor and the ridge to the north of Blencathra.

About the Author

Adrian vultur writes for windermere Spa Hotel

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