Geography GE2011: Glacial and Periglacial Processes Glacifluvial and glacilacustrine processes and landforms Recommended reading Benn, D.I. And Evans, D.J.A. (1998) Glaciers and Glaciation. Arnold, London, Marshak, S. (2001) Earth: Portrait of a Planet. Norton, New York,. Murray, T. (2005) Glaciers and ice sheets. In Holden, J. (ed.) Physical Geography and the Environment. Pearson, Harlow, ,.

1. Introduction Structure of lecture  Sources of water in glaciers  Drainage routeways  Glacial runoff regime  Glacifluvial erosion  Glacifluvial deposition  Glacial lakes NB Glacifluvial = fluvioglacial Nigardsbreen, Norway, June 2004

2. Sources of water on glaciers Surface sources:  Surface melt of snow and ice  Rainfall runoff  Lake discharge Basal and internal sources:  Melt of basal ice by geothermal heat  Frictional melt at glacier bed  Internal friction  Advective heat flux from meltwater  Subglacial groundwater

 Supraglacial streams  Moulins and crevasses  Englacial channels and conduits  Marginal & sub-marginal channels  Subglacial routeways:  Sheet flow (< 1mm thick)  Channels  Linked cavities  Braided ‘canals’  Proglacial streams 3. Drainage routeways Cold-ice glaciers do not have internal drainage routeways: supraglacial, marginal and proglacial routeways only. Supraglacial stream Subglacial stream

Drainage routeways (continued)…. Supraglacial runoff and ponding Moulin (glacial sinkhole)

Drainage routeways (continued)…. Ice-marginal stream draining into a proglacial lake Subglacial stream emerging at a portal at the glacier terminus

Drainage routeways (continued)…. Left: ice-marginal stream draining Mackensen Glacier, arctic Canada Left: subglacial stream emerging from Nigardsbreen, Norway Above: sub-marginal drainage at Schei Glacier, arctic Canada

4. Glacial runoff regime Discharge of the Schei River, arctic Canada, June to August No flow before late June Nival flood Diurnal discharge fluctuations Low air temperature in late July - low discharge Warmer air temperatures Rainstorms Only 2-3 months of runoff, but numerous flood events due to diurnal melt of snow and ice, and flashy response to rainstorms

Jokulhlaup: Glacial outburst flood, usually caused by breaching of an ice dam or moraine dam. Jokulhlaup on Sverdrup River, arctic Canada: discharge >2500 m 3 s -1 Left: jokulhlaup caused by volcanic eruption melting ice cap, Iceland

Meltwater streams are important geomorphological agents: Hydrologic regime - numerous short-lived flood events. Abundant readily-entrained glacigenic sediment (till, etc) - high sediment load and effective bed abrasion. Subglacial streams flow rapidly under hydrostatic pressure. 5. Glacifluvial erosion Glacifluvial erosion forms meltwater channels:

Marginal, submarginal and subglacial meltwater channels Submarginal channel, SkyeSubglacial channel, Lewis

Subglacial chutes Form when meltwater drops down a moulin then flows laterally across the glacier bed: Subglacial chutes at the foot of the Lomond Scarp Moulin

Col channels Form when a supraglacial or englacial stream is superimposed on to the underlying topography by ice-sheet downwastage:

Lake overflow channels Channels cut by drainage of a glacier-dammed lake across a col: Col channel, Strathrory, Easter Ross

Proglacial channels Formed by meltwater flowing from glacier termini. Many present rivers flow in former proglacial channels. Abandoned proglacial meltwater channel, Sør-Illabreen, Norway.

6. Glacifluvial deposition Characteristics of glacifluvial deposits are similar to those of alluvial deposits: 1.Often stratified (bedded) due to changing flow conditions: Glacifluvial deposits, Barrie, Southern Ontario

2. Clasts in glacifluvial deposits are usually rounded by abrasion

Glacifluvial deposits are a major source of sand and gravel for concrete, roads and other construction industries.

6.1 Depositional landforms Ice-contact glacifluvial landforms Origin of ice-contact glacifluvial landforms (from Strahler and Strahler, 2005)

Esker: course of a subglacial stream, infilled by glacifluvial sand and gravel. Kame: glacifluvial sands and gravels dumped from an englacial or supraglacial position

Kame terrace formed at former glacier margin, Ellesmere Island, arctic Canada Kame terrace Proglacial outwash plain (sandur)

Kettle holes (kettles) are enclosed depressions formed by: 1.Burial of blocks of stagnant glacier ice under glacifluvial or glacial sediments during glacier retreat. 2.Slow melting of buried ice to form an enclosed hollow. Developing kettle hole, Iceland Ancient kettle hole, Glen Ling, Scotland

6.1.2 Proglacial glacifluvial landforms: sandar (outwash plains) A sandur (plural sandar) is a glacifluvial floodplain. Sandur plain (outwash plain) - topographically unconstrained (e.g. southern Iceland): Valley sandur (outwash train) - forms a valley fill in mountain areas:

Characteristics of sandar  Braided channel network  Rapidly-changing flow - frequent avulsion  Downstream fining of gravel.  Sandar deposits laid down during rapid glacier retreat often form kettled sandar (pitted sandar).  Fluvial incision into sandar creates outwash terraces.

7. Glacial lakes (ice-dammed lakes) Form where glacier ice forms a barrier to drainage:  Range in size from small ponds to inland seas: Glacial Lake Agassiz (North America) covered 2,000,000 km 2.  Various locations:  Marginal lakes in ice-free tributary valleys  Trunk-valley lakes dammed by tributary valley glaciers  Glacier confluence lakes  Proglacial lakes.

Glacial lake dammed by Mackensen Glacier, Ellesmere Island: a trunk valley lake dammed by a glacier crossing a major valley. Landforms and deposits associated with former ice-dammed lakes  Shorelines formed at lake margins - usually indicate lake drainage via a outflow channel across a col.  Raised deltas, where streams entered the former lake.  Glacilacustrine deposits: fine-grained rhythmites containing dropstones.

The ‘parallel roads’ of Glen Roy: shorelines formed at three levels when a glacier dammed the mouth of the valley years ago End moraine Site of glacial lake Shorelines