Flashcards
Aeolian bedroom systems
Cards in this deck (18)
- 1Ripples 1Smallest aeolian bedfrom:
Most dry, bare, sandy surfaces (4 expectations)
Do NOT grow into dunes.
short-lived and have short geomorphic memories (10 mins for equilibrium).
Ballistic/ normal ripples. - 2Ripples 2Height/ wavelength of ripples are linked to grain size and U*
Ripples in coarse sand have greater wave length than fine sand.
Higher winds- larger variability of wave lengths & there are fewer waves. - 3Bagnold- Ripple formationBagnold (1941):
Proposed impact/ ballistic mechanism theory:
Ripples formed by saltation- spacing linked to saltation hop/path length.
Bagnold= too simplistic.
'Wave' length isn't the same as 'hop' length. - 4Ripple 'don't' form.....1) where sand is very coarse- supporting Bagnold)
2) at v. U* values.
3) in places where rainfall occurs.
4) where sand avalanches- (saltation doesn't occur).
Ripples can form ON dunes. - 5An Aeolian dune:Sub-aerial body of sand shaped by the wind.
A deposition landform
Inter-acts with airflows when certain size
Exhibits moprhxodynaimic feedback/ behaviour.
Dune initiation and development :
(Kocurek & Dott 1991)- mechanism- 1) accretion/ tractional deposition. - 6Dune formation Accretion/ tractional deposition1)Accretion/ traction deposition
2) Grain-fall deposition
3) Grain-flow deposition
Accretion/ tractional deposition:
Cessation of sand transport (saltation etc)
Occurs where shear stress of wind decreases downwind.
Wind decreased- less ability to transport - 7Grain-fallSand fallout of temporary suspension when previously saluting grain cross dune brink- deposition in lee due to rapid decrease in wind transport capacity.
Max deposition 0.2-0.4m from top of less face (<1m). - 8Grain-flowDeposition from rainfall leads to oversteepenign (bulge)at top of lee side
- eventually budge fails and avalanches down.
Once steep past a critcle angle repose (33 edges) the slope fails and flows down. - 9Dune typesFree-dunes/ desert - primarily controlled by wind & sediment supply. (star dunes, network dunes, linear dunes, transervse dunes & Barchans)
Anchored/ impeded dunes- significantly influenced or dependent upon vegetation, topography etc.
Coastal dunes- can include free dune types- e.g. transverse ridges
Ephemeral barchans are common. Dune assemblages- including embryo dune, fortune, transerve ridges, parabolic dunes, blowouts. - 10Coastal dune types“the only distinctive coastal dune is the fore-dune, because is is in many way different from all non-coastal dunes. In particular, a fortune is a dependent form that is integrally coupled to the complex suite of nearshore to the complex suite of nearshore processes fronting the beach-dune system”
(Bauer & Sherman 1999 p.73) - 11Distribution of coastal dunesWindward coasts with wide sandy beaches (e.g. Europe).
Near well-defined sea source areas e.g. aquitaine coast, france (grinder r.) dutch dunes (river rhine). - 12Incipient foredunes- new/ developing foredunes forming in pioneer plant communities
Development- F (plant density, distribution, height wind velocity etc.)
Secondary factors- Freq. of swash inundation etc. - 13Airflow over foredunes:Stoss side- flow line acceleration (air compressed).
On Lee side- sediment slows and there is sometimes re-circulation even.
Vegetation ^ drage and promotes sediment deposition.
Wind approaching a freduen at an obliques angle of b/w 30 & 60degrees- deflects towards crest- perpendicular.
Principle zone of sand deposition on a fordune caries as function of approach wind speed, veg cover and species topography. - 14Cross- sectional profile of fore-dunessSteep-slopes are caused by- under-cutting by th sea and avalanching
Flow separation- slip face formation
The steepest slope for dry sand (a slip face) is determined by the angle of repose of sand 32-34 degrees. - 15Airflow dynamics over foreduens PEI- Candada (hesp 2005)- READCS
- 16Coastal dune sequenceBeach
Foredune
Blowouts- Saucer- cup- or through - shaped depression or hollow formed by wind erosion on a pre-existing sand deposit. (steep erosional walls)- narrow entrance- depositional lobe.
Parabolic dune- wedge of sand moving in land. - 17Hesp 2002- 'causes of blow-outs'Wave-erosion along seaward face of dune
Topographic acceleration of airflow over dune crest.
Climate change- changes in salinity
Grazing
Human activities - 18Parabolic duneCrescentic or hairpin shaped sand accumulation
Horns pont upwind (opposite of barchans)
Can develop from blowouts.
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- Earth surface processes and landforms Flashcards on Aeolian bedroom systems, created by Lucy Harris on 14/06/2018.
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- Lucy Harris
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