Weathering and erosional landscape sculpture Flashcards
Describe the features of an erosional landscape.
-Dominated by uplift, weathering and erosion.
-Topographic relief.
-Covered in regolith and bare eroding rock.
What is Regolith?
A layer of loose, unconsolidated material covering solid bedrock produced by weathering processes.
What are the types of physical weathering?
-Freeze-thaw
-Exfoliation
-Action of plants
What are the types of chemical weathering?
-Hydrolysis
-Hydration
-Carbonation
-Oxidation
-Ion exchange
-Chelation
What factors control rates of weathering?
-Climate (warm and wet=fast chemical weathering)
-Rock Type (Soft & soluble rocks weather faster)
-Surface Area
-Biological Activity
-Topography (Steep slopes=physical weathering; flat areas=chemical weathering)
Where is regolith depth highest and lowest?
Regolith is highest at the equator, lowest at the subtropics and medium in temperate regions.
How is regolith growth self limiting?
-A reduction in grain size due to weathering and the formation of clays reduces permeability. This limits water access and slows chemical weathering.
-As erosion continues the slope angle decreases, slowing the rate at which regolith is removed and therefore new sediment exposed.
At weathering limited slopes what is the dominant process transport or weathering?
Transport
At transport limited slopes what is the dominant process transport or weathering?
Weathering
What are the two mechanisms for erosion?
1) Gravity (movement due to GPE)
2) Fluid flow (shear stress moves material)
Describe hillslope environments.
-Steep topography (secondary erosion).
-Presents hazards to life and infrastructure.
-Mainly subaerial environments but can be submarine.
What are the hillslope processes? (In order of decreasing gradient required)
Fall, slide, slump, debris flow and pyroclastic flow.
Fall
-Detachment occurs with little/no shear, movement due to free fall, bouncing or rolling.
-Common in glacial, canyon and sea-cliff areas.
-Talus slopes at the base of a cliff are a good indicator.
Slide
-Detachment and movement occurs along one or several surfaces of shear.
-Limited brittle internal deformation occurs (faulting).
Slump
-Detachment and movement occurs along one or several faces of shear.
-Brittle and ductile internal deformation (faulting and folding).
-An example is Mam Tor.
Debris flow
-Water saturated soi, sediment or regolith fails usually by catastrophic slumping.
-Kinetic energy imparted by the mass movement causes the grains to collide and bounce apart resulting in free flow.
-Very dangerous.
How do glaciers form?
Excess snowfall relative to ablation result in a build up of snow. The snow then compacts to form ice.
Why is ices erosional capacity much greater than waters?
It has a much greater viscosity.
How and what do glaciers erode and transport?
-Glaciers can erode and transport sediment of virtually any size.
-Material can move sub, en and supra glacially (below, in and on top).
-Melting and refreezing can pluck sediment.
-The weight of glaciers can pulverise rock.
-Sediment can be pushed along in front of a glacier.
How do glaciers change a landscapes morphology?
-Glaciers deepen and widen existing valleys flattening the base and steepening the sides.
-Deposited sediment is also dropped in an unsorted manner.
List some of the features of a relict glacial landscape?
-U-shaped valley
-Misfit rivers
-Hanging Valleys
-Cirques (hollowed amphitheatre like bowls)
-Aretes (steep ridges between two adjacent valleys)
-Pyramidal peaks
How do rivers undertake fluvial erosion?
Water imparts shear stress on particles and moves grains as bedload, suspended load and solvent.
What erosional processes occur in river environments?
-Erosion occurs vertically leading to hillslope processes and high weathering of soft rock.
-Canyon and gorge geomorphology
Newly established rivers
-Steep gradients.
-Erosion by downcutting and headward erosion.
Intermediate rivers
-Fully dissected former highlands.
-Extensive drainage network.
-Erosion occurs horizontally and develops a flood plain.
Mature rivers
-Wider flood plain.
-Peneplain forms (flat plain).
-Slopes retreat until they meet.
