A2.3GQ3 Glacial and Quaternary Geology LECTURE 3 HIGHLAND ACTIVE-ICE FEATURES

2 SUMMARY  The highland valley landsystem  Landsystem contrasts – Supraglacial debris supply – Climate – Ice dynamics  Frontal and lateral deposits – Debris-mantled glaciers – Clean glaciers  Coupling to the proglacial system

THE HIGHLAND VALLEY LANDSYSTEM

4 Glaciated valley assemblage  The highland valley landsystem develops when the glacier is contained within rock walls.  The depositional pattern is thus often controlled by the available area of the valley floor.  The defining feature is the the contribution of rockwall debris to the sediment load.

5  The original model was developed by Boulton & Eyles (1979) and made no distinctions between different mountain settings.  Subsequent work by Benn et al. (2005) indicated a contrast between ‘clean’ highland glaciers and those with debris-covered ablation zones.  This contrast has significant effects on the exact nature of the landsystem.

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LANDSYSTEM CONTRASTS Supraglacial debris supply

9  The supply and nature of the rockwall debris is identified as a major control on the development of the landsystem.  Significant factors include: – the rate of supply by weathering, landsliding etc – the general size of the debris particles – presence of clays

10  These are determined by the bedrock lithology and local climate – crystalline vs fissile (shale/slate) contrast – elevation or precipation contrast.

11 Glacier d’Argentière, France Photo: M.A.Paul

12 Rockwall debris - Himalaya

LANDSYSTEM CONTRASTS Climate

14  The clean vs dirty balance is also controlled by the input of snow relative to debris. – High relative input leads to the development of clean ablation zones – Low relative input leads to the development of debris-mantled ablation zones  The presence of a thick debris cover decreases the rate of ablation. Thus the ablation area will be larger relative to the accumulation area on debris-covered glaciers.

LANDSYSTEM CONTRASTS Ice dynamics

16  Clean vs dirty glacier snouts show a distinctive contrast in their response to changes in ice dynamics  Clean snouts show numerous frontal moraines superimposed on largely subglacial bedforms

17  These include: – ice-push and ice-squeeze features, such as annual moraines that arise from the winter advance into water-saturated debris – push/readvance (oscillation) moraines, due to decadal changes in mass balance

18 Breidamerkurjökull Iceland Photo: M.A.Paul

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20  Dirty snouts create multiple frontal moraines, often of great size.  These may be tectonically stacked, nested or superimposed.

21 Feegletscher, Switzerland Photo: M.A.Paul

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FRONTAL AND LATERAL DEPOSITS Debris-mantled glaciers

25  The principal landforms are the large latero- frontal moraines and the collapse features associated with them.  deposited by sliding and/or dumping.  not ice cored, not pushed (at first).  rockwall debris is usually angular, lacks subglacial rounding and faceting.

26  Sublacial landforms may exist but are often concealed beneath supraglacial debris.  There will be some reworking of debris by fluvial activity but ablation rates/area are slow (due to debris insulation) thus spatial density of reworking is limited.

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FRONTAL AND LATERAL DEPOSITS Clean glaciers

30  The principal landforms are subglacial in origin and reflect the glacier dynamics.  Supraglacial debris is limited and forms scattered cones and debris trains, perhaps associated with e.g. defined medial moraines.

31 Glacier des Boissons: France

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33 Buchananisen Spitsbergen Photo: M.A.Paul

34 Solheimajökull Iceland Photo: J.W.Merritt

35 Composite push ridges Breidamerkurjökull Photo: M.A.Paul

36  Some authors have suggested that the widespread ‘hummocky moraine’ of the Scottish highlands is an active-ice feature from interacting recessional ridges (Bennett & Boulton) or from local thrusting (Hambrey et al.) This implies clean ice.  Others (Sissons) believe it to be supraglacial and indicative of passive downwasting. This implies a supraglacial debris cover.

37 Probable push ridges Scottish Highlands Photo: J.W.Merritt

38 Hummocky moraine, Glen Torridon

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COUPLING TO THE PROGLACIAL SYSTEM

41  The proglacial system is the interlinked system of rivers and lakes by which meltwater is removed from the glacier.  This system also carries sediment by both water and mass flow and creates characteristic landforms and sediment bodies.  Meltwater streams can be powerfully erosive and create systems of channels, which may or may not be interconnected.

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43  An issue related to the clean/dirty ice model is the extent to which sediment discharge is coupled to the proglacial outwash system.  Large moraines often prevent drainage and create proglacial lakes. These act as sediment traps.  This causes the deposition of deltas and lake sediments. The meltwater streams leaving the area carry relatively little sediment.

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45  By contrast, clean glaciers lose much of their debris into the meltwater system since there is no way of trapping it.  This creates large spreads of fluvioglacial sediments as outwash terraces (sandar) which consist of overlapping fans.

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47  Over a period of time the degree of coupling may change, due to the destruction of moraine ridges and the consequent reorganisation of the local drainage system.  Several examples are provided by glaciers in western Spitsbergen during the past 100 years or so.

48 Elisabreen: Spitsbergen Norsk Polarinstitutt photo

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50 SUMMARY  The highland valley landsystem  Landsystem contrasts – Supraglacial debris supply – Climate – Ice dynamics  Frontal and lateral deposits – Debris-mantled glaciers – Clean glaciers  Coupling to the proglacial system

THE END

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