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Factors Affecting Erosion (FA Erosivity of Agents (Wind (Wind Direction …
Factors Affecting Erosion
FA Erosivity of Agents
Wind
Wind Direction
Sustained effectiveness of wind action, especially if unidirectional (yardangs)
During the :sunny: , winds move from cooler vegetated areas to bare surfaces due to the intense heating where low pressure is created
At :crescent_moon: , desert surfaces cool more rapidly than other regions and winds reverse their direction
Wind Turbulence
Wind can entrain sediments with its irregular motions and turbulent flow
Occurs in the form of eddy currents and directly influences entrainment processes
Generally only capable of lifting small-sized particles (slit/sands) of up to 0.125mm in diameter to elevations of 1.5m
Wind Velocity
Determines which sediments would be entrained (friction/ fluid threshold)
↑ with height above ground as it is slowed at the surface due to friction
Variations in surface conditions like particle size and human activities can cause changes in surface friction and influence aeolian processe
Wind Strength & Duration
Stronger and persistent winds can erode easily
Water
Duration
Longer rainfalls = more surface runoff = more erosion
Amount of annual rainfall
High amounts = more erosion
Intensity & Raindrop Size
Low intensity rain that lasts for long periods have
small raindrops
High intensity rain usually has
big raindrops
(resulting in most intense soil erosions)
Topography
Slope gradient can increase erosivity of both wind and water
Hillslopes: steeper, greater water action & slopewash, more erosion
Flat lowlands: More affected by wind
Potential ability of a geomorphic agent to erode
FA Erodibility of Surface
Surface Impediments
Presence of Vegetation
Sparse vegetation allows for free sweep of wind or water. Sediments easier to erode as it isn't bounded by vegetation to the surface
Densely vegetated areas are lightly eroded even if hit by intense storms
Destruction of Vegetation
Human activities like deforestation or urbanization where rainfall falls on exposed ground
Cultivated Agricultural covers where erosion is amplified and rate of sediment loss is ↑
Surface Crusts
Sediments are bounded to surface thus harder to erode as crust has to be broken first
Measure of the level of vulnerability of the surface material to erosion
Soil Characteristics
Soil Moisture
moist soil binds particles together making it harder for erosion
Rock Structure and Composition
unconsolidated or packed
fine or coarse (affects entrainment velocity)
particle size ; large or small
abrasiveness of sediments
Supply available
: large supply promotes erosion
:wind_blowing_face:
Wind BWh
High wind erosivity
Persistent strong winds
Extreme aridity
High surface erodibility
Barren exposed slopes with no vegetation for free sweep of wind
Supply of abrasive unconsolidated sediment for deflation
Easily forms yardangs on weak erodible rock surfaces thru abrasion
NOT common in semi-arid due to presence of vegetation that impedes wind erosion
Erosion
is a combination of agent erosivity and surface erodibility
Uncommon in Af/Am/Aw
Wind erosivity modified due to vegetation
Although rainfall is intense and frequent, vegetation binds sediments to surface causing low surface erodibility to both wind & water
High infil rates = lack of sustained surface runoff
:thunder_cloud_and_rain:
Water BSh
High water erosivity
Usually during or shortly after a heavy downpour during the high intensity rainfalls of its short wet seasons, amounting to more than 400mm/year
Thin soils & sparse vege thus low infiltration rates & large vols of surface runoff
High surface erodibility
Barren desert surfaces of sparse vegetation & poor soil cohesion
Easily forms rills & gullies
NOT common in BWh
Unsustained surface runoff from little rainfall & high evpt rates
Low surface erodibility to water erosion as hillslopes largely covered by hard bedrock