Geography GE2011: Glacial and Periglacial Processes

1
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, .
2
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
3
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

4
3. Drainage routeways

• Supraglacial streams
• Moulins and crevasses
• Englacial channels and conduits
• Marginal sub-marginal channels
• Subglacial routeways
• Sheet flow (lt 1mm thick)
• Channels
• Linked cavities
• Braided canals
• Proglacial streams

Supraglacial stream
Cold-ice glaciers do not have internal drainage
routeways supraglacial, marginal and proglacial
routeways only.
Subglacial stream
5
Drainage routeways (continued).
Supraglacial runoff and ponding
Moulin (glacial sinkhole)
6
Drainage routeways (continued).
Ice-marginal stream draining into a proglacial
lake
Subglacial stream emerging at a portal at the
glacier terminus
7
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
8
4. Glacial runoff regime
Discharge of the Schei River, arctic Canada, June
to August
Warmer air temperatures
Diurnal discharge fluctuations
Rainstorms
Low air temperature in late July - low discharge
No flow before late June
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
9
Jokulhlaup Glacial outburst flood, usually
caused by breaching of an ice dam or moraine dam.
Jokulhlaup on Sverdrup River, arctic Canada
discharge gt2500 m3 s-1
Left jokulhlaup caused by volcanic eruption
melting ice cap, Iceland
10
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
11
Marginal, submarginal and subglacial meltwater
channels
Submarginal channel, Skye
Subglacial channel, Lewis
12
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
13
Col channels
Form when a supraglacial or englacial stream is
superimposed on to the underlying topography by
ice-sheet downwastage
14
Lake overflow channels
Channels cut by drainage of a glacier-dammed lake
across a col
Col channel, Strathrory, Easter Ross
15
Proglacial channels
Formed by meltwater flowing from glacier
termini. Many present rivers flow in former
proglacial channels.
Abandoned proglacial meltwater channel,
Sør-Illabreen, Norway.
16
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
17
2. Clasts in glacifluvial deposits are usually
rounded by abrasion
18
Glacifluvial deposits are a major source of sand
and gravel for concrete, roads and other
construction industries.
19
6.1 Depositional landforms
6.1.1 Ice-contact glacifluvial landforms
Origin of ice-contact glacifluvial landforms
(from Strahler and Strahler, 2005)
20
Esker course of a subglacial stream, infilled by
glacifluvial sand and gravel. Kame
glacifluvial sands and gravels dumped from an
englacial or supraglacial position
21
Kame terrace
Proglacial outwash plain (sandur)
Kame terrace formed at former glacier margin,
Ellesmere Island, arctic Canada
22
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
23
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
24
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.

25
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.

26
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.

Glacial lake dammed by Mackensen Glacier,
Ellesmere Island a trunk valley lake dammed by a
glacier crossing a major valley.
27
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