Conclusion

Research has shown that the active temperate glacial landsystem is composed of three depositional domains (Fig. 2.20). First, areas of extensive, low-amplitude marginal dump, push and squeeze moraines are derived largely from material on the glacier foreland. These moraines often record annual recession of active ice but some may be superimposed during periods of ice margin stability. The continuation of flutings over the proximal slopes and crests of many push moraines indicates that subglacial bedform and push moraine production is genetically linked. A subglacial deformation/ploughing origin of flutings thereby implies that push moraines are

Figure 2.18 Active temperate glacial landsystems of southern Alberta, Canada. A) Maps of southern Alberta showing major moraine systems and locations of three ice sheet lobes. (After Evans et al., 1999a). W = west, C = central, E = east lobes; the Frank Lake/Granum and Milk River areas are boxed. B) Part of an aerial photograph mosaic of the Frank Lake area of southern Alberta, showing prominent recessional moraine ridges typical of the southern margins of the west lobe. Eskers and flutings are also well developed in the area (e.g. Evans et al. 1999a). C) Part of an aerial photograph of the Milk River drainage basin near Pendant d'Oreole, Alberta, Canada, showing numerous extensive and closely spaced recessional push moraines. In the same area more widely spaced push moraines are associated with flutings and drape overridden push moraines.

Figure 2.18 Active temperate glacial landsystems of southern Alberta, Canada. A) Maps of southern Alberta showing major moraine systems and locations of three ice sheet lobes. (After Evans et al., 1999a). W = west, C = central, E = east lobes; the Frank Lake/Granum and Milk River areas are boxed. B) Part of an aerial photograph mosaic of the Frank Lake area of southern Alberta, showing prominent recessional moraine ridges typical of the southern margins of the west lobe. Eskers and flutings are also well developed in the area (e.g. Evans et al. 1999a). C) Part of an aerial photograph of the Milk River drainage basin near Pendant d'Oreole, Alberta, Canada, showing numerous extensive and closely spaced recessional push moraines. In the same area more widely spaced push moraines are associated with flutings and drape overridden push moraines.

the product of the advection of subglacially deforming sediment to the ice margin where squeezing and pushing then combine to create the moraine ridge. Larger push moraines can be constructed by stationary glacier margins. A variety of processes may be involved in the production of larger moraines including the stacking of frozen sediment slabs, the prolonged

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Figure 2.19 A) Map of recessional push moraines, many with saw-tooth plan forms, on the south shore of Lake Pukaki, New Zealand. Small areas of flutings are visible between moraine ridges, and channelled sandur are partially routed between moraines. B) Photograph and detailed section sketches (located by boxes on the photograph) of the glacitectonized fluvial and lacustrine sediments and overlying subglacially deformed materials (glacitectonite) that constitute the main ridge over which the recessional moraines at Lake Pukaki have been draped. Note the undeformed core of coarse gravels at the base of the section.

Figure 2.19 A) Map of recessional push moraines, many with saw-tooth plan forms, on the south shore of Lake Pukaki, New Zealand. Small areas of flutings are visible between moraine ridges, and channelled sandur are partially routed between moraines. B) Photograph and detailed section sketches (located by boxes on the photograph) of the glacitectonized fluvial and lacustrine sediments and overlying subglacially deformed materials (glacitectonite) that constitute the main ridge over which the recessional moraines at Lake Pukaki have been draped. Note the undeformed core of coarse gravels at the base of the section.

Glacial Facies

Figure 2.20 The active temperate glacial landsystem. Landforms are numbered according to their domain: 1 = morainic domain, 2 = glacifluvial domain, 3 = subglacial domain, 1a = small, often annual push moraines, 1b = superimposed push moraines, 1c = hummocky moraine, 2a = ice-contact sandur fans, 2b = spillway-fed sandur fan, 2c = ice margin-parallel outwash tract/kame terrace, 2d = pitted sandur, 2e = eskers, 2f = entrenched ice-contact outwash fans, 3a = overridden (fluted) push moraines, 3b = overridden, pre-advance ice-contact outwash fan, 3c = flutes, 3d = drumlins. The idealized stratigraphic section log shows a typical depositional sequence recording glacier advance over glacifluvial sediments, comprising: I = undeformed outwash, II = glacitectonized outwash/glacitectonite, III = massive, sheared till with basal inclusions of pre-advance peat and glacifluvial sediment, IV = massive sheared till with basal erosional contact. (After Kruger 1994a; Evans and Twigg, 2002).

Figure 2.20 The active temperate glacial landsystem. Landforms are numbered according to their domain: 1 = morainic domain, 2 = glacifluvial domain, 3 = subglacial domain, 1a = small, often annual push moraines, 1b = superimposed push moraines, 1c = hummocky moraine, 2a = ice-contact sandur fans, 2b = spillway-fed sandur fan, 2c = ice margin-parallel outwash tract/kame terrace, 2d = pitted sandur, 2e = eskers, 2f = entrenched ice-contact outwash fans, 3a = overridden (fluted) push moraines, 3b = overridden, pre-advance ice-contact outwash fan, 3c = flutes, 3d = drumlins. The idealized stratigraphic section log shows a typical depositional sequence recording glacier advance over glacifluvial sediments, comprising: I = undeformed outwash, II = glacitectonized outwash/glacitectonite, III = massive, sheared till with basal inclusions of pre-advance peat and glacifluvial sediment, IV = massive sheared till with basal erosional contact. (After Kruger 1994a; Evans and Twigg, 2002).

impact of dump, squeeze and push mechanisms at the same location, or the incremental thickening of an ice-marginal wedge of deformation till. Wide and arcuate, low-amplitude ridges that are draped by flutings and recessional push moraines are interpreted as glacially streamlined push moraines overridden by glaciers during major readvances. The general lack of supraglacial sediment in active temperate glaciers generally precludes the widespread development of chaotic hummocky moraine, although low-amplitude, bouldery hummocks are produced by the melt-out of medial moraines and by the melting of debris-charged glacier snouts in settings where marginal freeze-on produces debris-rich ice facies.

Second, subglacial landform assemblages of flutings, drumlins and overridden push moraines dominate the land surfaces between ice-marginal depo-centres because the veil of supraglacial sediments is generally very thin and discontinuous. Although tills are thin over topographic high points in areas of hard bedrock, the stratigraphy of subglacial materials often displays a vertical continuum comprising glacitectonized stratified sediments of outwash and/or glacilacustrine origin capped by lodgement/deformation till containing rafts of underlying material and the products of localized abrasion. Complex till sequences thicker than 2 m are constructed by the sequential plastering of several till layers similar to rheologic superposition (Hicock, 1992; Hicock and Dreimanis, 1992; Hicock and Fuller, 1995) and the till/stratified interbed successions of Eyles et al. (1982), Evans et al. (1995), and Benn and Evans (1996). The ubiquitous flutings of the forelands are traditionally explained as the products of till squeezing into cavities on the down-glacier sides of lodged boulders (Boulton, 1976; Benn, 1994). Larger drumlins have been explained by Boulton (1987) as the streamlined remnants of coarse-grained sandur fans based upon the surface forms and internal stratigraphy of the BreiSamerkurjokull foreland.

Third, glacifluvial landforms are often extensive and include sandur fans (both ice-contact and spillway fed), ice margin-parallel outwash tracts and kame terraces, topographically channelized sandar, pitted sandar (ice-marginal and jokulhlaup types), and eskers of single and more complex anabranched forms. Although hummocky terrain located at receding glacier margins is often referred to as kame and kettle topography it can evolve through time due to melt-out of underlying ice into complex networks of anabranched eskers. The lowering of esker surfaces through time clearly demonstrates that they largely originated englacially or supraglacially.

The clear landform-sediment signatures of active temperate glacier recession have been recognized in some ancient glaciated terrains and can potentially provide glacial and Quaternary researchers with invaluable information about glacier dynamics and their linkages to climate change. In ancient glaciated basins where the landsystems approach has enabled us to recognize the imprints of active temperate glaciation, we are dealing with a landform-sediment record that possesses a clear regional palaeo-climatic signal rather than a glacial legacy that is dictated purely by localized physiographic controls and/or changes in the internal dynamics of the glacier system.

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