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Glaciers and Glaciation > Week 12: Glacifluvial processes and landforms > Flashcards

Week 12: Glacifluvial processes and landforms Flashcards

1
Q

“Chaos”

A

Ice-contact environments have glacifluvial sediment and meltwater processes

As meltwater evolves over time, the tunnels carrying the water are also constantly evolving/changing shape

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2
Q

Kames =

A

sand/gravel deposits

Chaotic distribution

Hummocky mounds

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3
Q

Ice-walled lake plains =

A

accumulations of sediment in larger holes created within a glacier over time

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4
Q

Sandur =

A

flat outwash plains of sand/gravel

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5
Q

Spatial/temporal continuum

A

Glacifluvial landform assemblages occupy positions on this continuum

Series of tunnels/cavities working their way through ice

Constantly depositing sediment in ‘temporary’ holes

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6
Q

How do drainage networks in receding glaciers evolve?

A

Enlarge drainage pathways

Amalgamating drainage pathways

Switching from hydrostatic to atmospheric pressure

  • as ice downwashes
  • from fully subglacial system to supra/en/sub
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7
Q

Example of evolution of a glacier drainage network

A

R-channel esker

(pressure change)

H-channel esker

(tunnel collapse = completely open to atmosphere)

Ice-walled channel fill

(ice surface drainage)

Kame and kettle topography

Proglacial sandur progradation

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8
Q

Types of esker infills

A

R-channel

H-channel

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9
Q

Esker R-channel infill

A

Under hydrostatic pressure = water forced to flow uphill

= hummocky long profiles going up and down slopes

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10
Q

Esker H-channel fill

A

Under atmospheric pressure = aligned with bed slope

N.B. Includes ‘valley eskers’

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11
Q

What causes an esker to have an undulatory long profile?

A

Individual cavities within ice are filled up before moving along to next segment

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12
Q

Possible planforms of eskers

A
  1. Single continuous ridges (uniform cross-sectional profile)
  2. Single ridges of variable height/width
  3. Single low ridges linking numerous mounds/beads
  4. Complex braided systems
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13
Q

Relationship of eskers to ice flow

A

USUALLY ASSUMED ALIGNED // OR SUB-// TO ICE FLOW

BUT can be transverse e.g. valley esker Oldufelsjokull

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14
Q

Evidence of eskers deposited in segments during ice sheet retreat

A

Long ridges punctuated by ice marginal features

Dispersal centre = void area with radial patterns of eskers coming from it
e.g. Keewatin divide

Equidistant tunnels, spacing out the drainage system

Become more frequent during deglaciation due to increased rates of ice margin recession and climate warming

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15
Q

Example of mapping eskers

A

20,000 mapped by Storrar et al 2014 on Laurentide Ice Sheet

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16
Q

Boulton et al explanation of incremental deposition of eskers (N.B. Can also be continuous)

A

2007: Breidamerkurjokull

  • Tunnel axis remains stable
  • Strong coupling between groundwater and summer meltwater
  • Open/shut due to flotation/water pressure decoupling of glacier
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17
Q

Hooke and Fastook explanation of incremental deposition of eskers

A

2007: S Laurentide ice sheet

  • Tadpole shape (narrow further back from margin)
  • separate deposition of each segment in sub-marginal tunnel
  • melt/sedimentation rates increase with increasing glacier margin surface slope
  • melt rates exceeds tunnel closure rates towards margin = reduce water flow (larger tunnel) = deposition
18
Q

Esker sediments

A

Silts to boulders/diamictons
Bedded sands and gravels
Cut and fill sequences
Cyclical patterns

Bedform/discharge changes due to:

  • glacier melt patterns
  • tunnel constrictions and cavities
19
Q

Cut and fill =

A

channel cut through pre-existing sediment then deposits

20
Q

Supraglacial eskers

A

aka interlobate ‘moraines’

Occurs where amount of supra glacial sedimentation overwhelms everything else

  • initially sub/en
  • evolve = supra glacial ridges
  • widen = supraglacial lakes with interlobate moraines
  • later stages of evolution = kame and ice-walled lake plain
21
Q

Example of supra glacial esker/interlobate moraine

A

Harricana Moraine, Laurentide Ice Sheet 1000km long, <10km wide, <100m high

22
Q

Jokulhlaup and surge eskers

A

If tunnel opens up into series of restricted/less restricted zone = escape of water into snout

= zig-zag eskers (crevasse infills)

23
Q

What do the limbs of crevasse infills represent?

A

A crevasse that water surged into and deposited an esker

24
Q

Jokulhlaup and surge esker example

A

1996 Skeidararjokull jokulhlaup

25
Q

What happens at the esker tunnel/lake interface?

A

Sediment splays into cavities due to flotation of tunnel mouth
= beaded eskers

26
Q

Classification of kames

A

Terraces

Hills

Plateaus/ice-walled lake plain

27
Q

Kame and kettle topography =

A

fluvial deposition on wasting glacier surface

Guided by controlled ridges of debris-charged ice and infilling of glacier karst

28
Q

Kettle hole =

A

Discontinuous surface due to collapse beneath

= heavily disturbed stratified sediments

29
Q

Kame terraces =

A

ice-marginal stream beds

  • normal faulting and kettle holes
  • accordant surfaces
    (appear as terrace from a distance)
30
Q

Ice-walled lake plains (kame plateau) =

A

circular plateau juxtaposed with chaotic kames/eskers/hummocky moraines

Partially flooded elongate channels between

= locally disturbed lake and glacifluvial sediments

31
Q

Ice-walled lake plain (kame plateau) genesis

A
  • infills of glacier karst holes
  • melting of surrounding ice
  • = upstanding plateau with collapsed sides
32
Q

Stable ice-walled lake plains

A

Debris-charged ice

33
Q

Unstable ice-walled lake plains

A

Debris-poor ice

  • if hardly any sediment a pancake of sediment is recorded in landscape = hardly noticeable
    = decreases preservation potential
34
Q

Sandur =

A

Proglacial outwash fan

Braided channel network

High discharge for short periods of time

Downstream fining

35
Q

Sandur; proximal zone

A

Few deep and narrow channels carrying sediment in their water

36
Q

Sandur; intermediate zone

A

Complex network of wide/shallow braids with many channels abandoned

37
Q

Sandur; distal zone

A

Very shallow, ill defined channels only flooded by sheet flow at high discharges

38
Q

How do pitted sandar form?

A

1) Proximal outwash buries glacier snout
- N.B. overlap with kame/kettle topography

2) Ice blocks buried on jokulhlaup sander and melted out

Relates to melting of ice

39
Q

Example of pitted sandar

A

Myrdalssandur 1918 flood deposits

40
Q

Glacifluvial successions

A

Miall 1977, 1978

Trollheim

Scott

Donjek

Platte

Glaciers and Glaciation (29 decks)

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