Hummocky moraine

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.

The most accessible examples of hummocky moraine are in the Pass of Drummochter (Lukas, 2002). Here the complexes of hummocks, ridges and meltwater channels are well seen from the A9, especially in the late morning after light snow. The internal structure of the hummocks and ridges is seen in stream sections. The hummocks are generally composed of blocky till in a matrix of grit and sand and blocks often occur on the surface of the mounds. Occasionally, the hummocks contain washed sediment and the associated folding and faulting of beds indicate push by ice.

Detailed mapping has shown the hummocks in Cairngorm glens to be part of integrated systems of small ridges and meltwater channels that indicate active recession of valley glaciers (Bennet, 1996).

Sissons (1979) regarded hummocky moraine in the Cairngorms as diagnostic of the former presence of stagnating valley glaciers at the termination of the Loch Lomond Stadial. The existence of hummocky moraine around Loch Builg, well outside the LLS glacial limits, indicated however that this association was over simplified (Clapperton et al., 1975).