Terminal moraines

Present and former positions of glaciers are marked by different moraine types formed by the deposition of sediment at the margins, or by stresses induced by the glaciers. Such deposits exhibit a number of features, such as glacitectonic landforms, push and squeeze moraines, dump moraines, and later/frontal fans and ramps. It is often difficult to classify ice marginal deposits. Moraines of supraglacial and englacial origin are difficult to recognize because the material is lowered on to the ground during the retreat of the glacier margin. The outer moraine ridge formed at the limit of the glacier advance is commonly termed the terminal moraine, while younger moraines within the terminal moraine are called recessional moraines. Recessional moraines form during minor advances or stand-stills during general retreat. Terminal and recessional moraines my be subdivided into frontal and lateral parts, or latero-frontal moraines. Recessional moraines formed on a yearly basis are termed annual moraines.

The ability of glaciers to deform bedrock and sediments into thrust moraines and sheets has been known since early Quaternary studies from Sweden, Denmark, Germany, Poland, the UK and North America (e.g. Aber et al, 1989). Four basic types of glacitectonic landforms are recognized: (a) hill-hole pairs; (b) composite ridges and thrust block moraines; (c) cupola hills; and (d) megablocks and rafts.

Push moraines are normally small moraine ridges (usually less than 10 m high) formed during minor glacier advances. These moraines can form either at subaqueous or terrestrial ice margins. Cross-sections of push moraines are often asymmetric with gentle proximal and steep distal slopes. Push moraines are broadly arcuate in form, but small-scale morphological features reflect the morphology of the glacier margin. At glacier margins with radial crevasses, push moraines have a characteristic saw-tooth shape.

Material accumulating on the glacier surface is subject to remobilization by mass flow, sliding, falls or fluvial transport. The remobilization may result in dumping of the material during the glacier recession. Dump moraines therefore form where the ice margin remains stationary during debris accumulation (Boul-ton and Eyles, 1979).

Debris flows and glaciofluvial processes around stationary glacier margins may form latero-frontal fans and ramps. The distal slopes of such forms have lower gradients than dump moraines. The proximal slopes are, however, steep, reflecting the former ice-contact face.

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