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, 98-139.

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, 440-446, .

1. Introduction

Structure of lecture

Sources of water in glaciers

Drainage routeways

Glacial runoff regime

Glacifluvial erosion

Glacifluvial deposition

Glacial lakes

NB Glacifluvial = fluvioglacialNigardsbreen, 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 m3 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, Skye Subglacial 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

6.1.1 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 km2.

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 12000 years ago

End moraine

Site of glacial lake

Shorelines