Erosional & Depositional Fluvial Landforms Flashcards
Depositional fluvial landforms: (4)
Flood plains,
Deltas,
Alluvial fans,
Terraces.
Erosional: Valleys - (5)
V shaped.
Flowing water erodes deep into bedrock to form a valley.
Over steepening of sides causes collapse, creating slopes on either side of channel.
Creation of new drainage basin.
Alluvial fans: (3)
Water spreads out, hydraulic radius is reduced.
Semi-conical shape.
Localised deposits.
Alluvial fans: Sudden decrease in gradient =
Reduction in water speed and deposition of stream load.
Alluvial fans: A stream loaded with sediment
Emerges from a confined mountain valley onto a flat unconfined plain.
Terraces: A result of a drop in
Base level, causes stream to erode further downwards, thus creating a new lower floodplain.
Terraces: Are abandoned
Floodplains formed when a river becomes graded below the present level.
Unpaired terrace: Occurs when stream has shifted from
One side of the valley to the other, the sides are different ages.
Unpaired terrace: reveals episode of
Single down cutting that alternated between valley sides.
Paired terrace: Periods of
Vertical erosion and deposition, followed by down cutting.
Terraces: The distinction between
Paired and unpaired terraces can show a streams history and evolution.
Deltas: Foreset layer -
Forms when lakebed slopes at sharper angle than the stream channel.
Deltas: Bottomset layer - (3)
Thinner and finer,
Gradient is less,
As more layers are deposited, stream channel slowly migrates out over the extending delta.
Deltas: Water from a stream reaches a
Still lake and slows down. Its load is deposited in order of decreasing mass, courser material is deposited near stream mouth, finer material is further offshore.
Flood plains: Repeated flooding =
Build up of material, creating banks and natural levees.
