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 = 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
3. Drainage routeways
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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
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
Above: sub-marginal drainage at
Schei Glacier, arctic Canada
Left: subglacial stream emerging
from Nigardsbreen, Norway
4. Glacial runoff regime
Discharge of the Schei River,
arctic Canada, June to August
Diurnal
discharge
fluctuations
No flow
before
late June
Warmer air
temperatures
Low air
temperature
in late July low discharge
Rainstorms
Nival flood
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
5. Glacifluvial erosion
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.
Glacifluvial erosion forms
meltwater channels:
Marginal, submarginal
and subglacial
meltwater channels
Submarginal channel, Skye
Subglacial channel, Lewis
Subglacial chutes
Moulin
Form when meltwater
drops down a moulin then
flows laterally across the
glacier bed:
Subglacial chutes
at the foot of the
Lomond Scarp
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
Proglacial outwash plain (sandur)
Kame terrace formed at former glacier margin, Ellesmere
Island, arctic Canada
Kettle holes (kettles) are
enclosed depressions
formed by:
1. Burial of blocks of
stagnant glacier ice
under glacifluvial or
glacial sediments
during glacier retreat.
Developing kettle hole, Iceland
2. Slow melting of buried
ice to form an enclosed
hollow.
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.
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.
Glacial lake dammed by Mackensen
Glacier, Ellesmere Island: a trunk valley
lake dammed by a glacier crossing a
major valley.
 Raised deltas, where
streams entered the
former lake.
 Glacilacustrine deposits:
fine-grained rhythmites
containing dropstones.
Shorelines
Site of glacial lake
End moraine
The ‘parallel roads’ of Glen Roy: shorelines formed at three levels
when a glacier dammed the mouth of the valley 12000 years ago