A deep linear feature, carved into bedrock by glacial erosion that is channelled along a trough or valley. Troughs may be cut beneath ice sheets by a combination of glacial abrasion and quarrying. The effects of glacial abrasion are more obvious on the smoothed and polished trough walls whilst the effects of glacial quarrying—such as roches moutonnées and rock basins—are most evident on the valley floors. Glasser and Bennett (2004) PPG 28, 3 see troughs as palimpsest features, developed over successive glaciations.
Hebdon et al. (1997) ESPL 22 calculate glacial erosion rates as between 1 and 2 mm a−1 in Scotland; Harbor et al. (1988) Nature 333 cite rates of 10−3 ma−1 landslide material in a single glacial cycle.
Although the cross-sectional form of a glacial trough is traditionally described as ‘U-shaped’, their true cross-sectional morphology is better described by empirical power-law functions (Yingkui et al. (2001) J. Glaciol. 47) and by second-order polynomials (James (1996) ESPL 21). Furthermore, this cross-sectional morphology varies with lithology (Harbor (1995) Geomorph. 14), rock mass strength (Brook and Tippett (2002) Scot. J. Geol. 38, 1) and the degree of alluvial modification (James op. cit.).
Modelling studies demonstrate that the cross-sectional morphology of glacial troughs tends towards an equilibrium form (Harbor (1992) GSA Bull. 104). Other characteristics of glacial troughs include classic features of glacial erosion such as hanging valleys and divide elimination (Linton in H. E. Wright and W. H. Osburn, eds 1967), whilst the valley patterns associated with these features have been used to quantify the effects of glacial erosion on landscapes (Haynes (1995) Boreas 24).