Sandar and Valley Trains

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Sandar and Valley Trains

• Presented By Rik Anaka

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What is a Sandur?

• Icelandic for Sandy Area
• Proglacial feature
• Often termed outwash plain
• Unconstrained by topography
• Fluvial transport of sediment onto broad plain
• Braided streams
• Skeidarársandur in southern Iceland

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Landsat Satellite Image of Skedarársandur in
southern Iceland Source http//en.wikipedia.org/w
iki/Sandur
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What is a Valley Train?

• Similar to a sandur except that it is constrained
  by topography
• Usually found in alpine environment at the mouth
  of an outlet glacier
• Braided streams
• Saskatchewan Glacier pro-glacial plain
• Most valleys that have been glaciated show some
  evidence of valley train altering

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Saskatchewan Glacier Valley Train Banff
National Park Source Google Earth
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Athabasca Glacier and Valley Train
Saskatchewan Glacier and Valley Train
Saskatchewan Glacier Valley Train (Overhead
View) Source Google Earth
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Formation and Morphology of a Sandur

• Main aggregation agent is jökulhlaup event
• Can also be aggregated (to a lesser scale) by
  heavy precipitation events
• Initial deep channel
• After discharge slows, water flow spreads out and
  slows allowing sediment loan to be deposited
• Large particles (boulders, coarse gravel) near
  glacier
• Smaller particles (silts and clays) near terminus
  of sandur
• Vegetation is absent or sparse on sandur plain

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Idealized Horizontal Profile of a Sandur

• Note Large sediment near glacier, medium sized
  sediment in the middle, and smallest sediment
  near terminus
• Note Braided stream network. The stream flow is
  centralized near snout of glacier, but braids as
  it spreads out and looses velocity.

Source van Loon, Zielinski, 2002
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Cross Section Drawing of a sandur and surrounding
area Source http//www.geo.msu.edu/geo333/outwash
_plains_html
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Sandur sediment Profile A) near glacier
B) middle of sandur C) near terminus
C
eastern Scotland Source Marren, 2005
Skedarársandur, Iceland Source Marren, 2005
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Sandur surface near glacier mouth Mýrdalssandur,
southern Iceland Source http//www.eos.ubc.ca/kr
ussell/subglacial/images/00-1-13.html
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Formation and Morphology of Valley Trains

• Main aggregation agent is deposition of sediments
  in braided stream system
• Rate of aggregation depends on discharge and
  sediment load of streams
• Both braided stream system and valley train is
  constricted within the walls of the valley
• Can bury entire moraines
• Terrace formation in old valley trains

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Skeidarársandur

• Located in southern Iceland
• Largest sandur in Iceland approx. 1300km²
  (Finnegan, et. al., 2002)
• Most extensively studied sandur
• Periodic jökulhlaup draining of Lake Grimsvötn
• Proglacial feature of Skeidarájökull glacier,
  part of the Vatnojökull ice cap

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Skeidarársandur
Source http//en.wikipedia.org/wiki/Sandur
Source Finnegan, et. al., 2002
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Controversy

• Like all glacial research there is controversy
  related to sandur and valley train development
• van Loon, and Zielinski (2002)
• Modern sandar develop differently that older
  sandar
• Sandar development is mainly due to braided
  stream aggregation rather than jökulhlaup events
• Sandar have similar development as alluvial fans

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Controversy

• Marren wrote a reply in 2004 dismissing van Loon
  and Zielinskis findings
• Argued that their finding were based on
  incomplete data, outdated models, and
  inappropriate models
• Argued that van Loon and Zielinskis sites were
  inappropriately located
• Stated that more sandur features should be
  studied before an accurate assessment regarding
  morphology can be made.

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Thank You!

• Questions?