Definition: a strongly undulating surface of ground moraine, with a relative relief of up to 10 m, and showing steep slopes, deep, enclosed depressions and meltwater channels. It results from the downwasting (i.e. thinning) of ice which may be stagnant or active. Blocks of ice may squeeze debris released from the ice into crevasses between the blocks.

Hummocky and streamlined drift mounds in Harray

The interior of a drift mound

Hummocky moraine has been regarded as diagnostic of the former presence of stagnating valley glaciers at the termination of the Loch Lomond Stadial (Sissons, 1979) regarded. More recent detailed mapping has shown that the hummocks in many Scottish glens are part of integrated systems of small ridges and meltwater channels that indicate active recession of valley glaciers (Bennet, 1996) and that hummocky moraine also formed during deglaciation.

On Orkney, hummocky drift occurs on parts of Hoy and Rousay but reaches its most extensive development in Harray. Here extensive areas of ground show low hummocks, mostly less than 100 m long and 5 m high, oriented between N and W. Some retain boulders on their surfaces and others may have been lost to agricultural improvement. Available exposures are sufficient to indicate that the the hummocks often have a core or base of bedrock and consist of locally-derived, rubbly till. No detailed mapping has been completed of these mound system. It is uncertain as to whether the terrain should be interpreted as hummocky moraine formed beneath stagnant ice or drumlin fields streamlined by active ice flow.

  • Westray is the furthest northwest of the Orkney islands. The total area is 47 square kilometres, not huge but the irregular shape gives it a long coastline of almost 80 kilometres, a good place to look for glacial striations. The bedrock of the whole of the island is made up of the cyclical Rousay Flagstone Formation. ...

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  • Glacial deposition is largely confined to low-lying areas on Orkney, where thicknesses of till may exceed 10 m. The glacial deposits drape the landscape, smoothing its outlines. Ice-marginal features are largely unrecognised outside Hoy ...

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  • In the gently-dipping sandstone terrain of Orkney, it is often difficult to pick out classic landforms of glacial erosion. Low-lying areas often show a pronounced SW-NE grain to the topography, parallel to the main direction of ice sheet flow. ...

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  • During the periods of maximum cold in the Quaternary, major ice sheets covered Scotland. An ice stream hundreds of metres thick curved out from the Moray Firth to cross the plain of Caithness and flow over Orkney towards ice limits close to the edge of continental shelf.

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