Slope as an Open System
A slope is an open system because various processes occur on slope determining its form and or shape. The processes can be grouped into Endogenic( controlled by internal factors and occurring below the surface) and Exogenic( controlled by external factors and occurring on the surface).
Exogenic Factors
Climate
Climate plays a pivotal role in shaping slopes. Its a broad term covering temperature and precipitation. Climate also influence weathering types and vegetation density.
Arid regions often have steep and rugged scarps uncovered by debris as mechanical weathering is more pronounced. Lees rainwater has left most of the steep Grand Canyon sides (scarps) intact . Insufficient water lessens chemical reactions to decompose slopes or destroy steep scarps. In periglacial (cold) areas steep scarps dominate but frost action may destroy them
In tropic and sub-tropic regions abundant water weathers rocks producing more debris and gentler slopes. See deep weathering
Vegetation
Sparse vegetation means loose soil and high run-off which can give gentler slopes. Conversely, in a densely vegetated area soils are more bound together and slope steepness is maintained. Tropical areas often exhibit gentler slopes as vegetation holds the weathered mantle in position.
Slope Processes
Slope processes range from overland flow to through flow to rainsplash to mass movement and more. Slopes can be divided into transport limited and supply limited.
On transport limited slopes sediment is produced more than it can be removed. For example, soil creep accumulates debris at the slope base which grows and engulfs the middle slope gradually lowering the slope.
Debris can also be produced by rainsplash, sheetwash and solifluction.
Supply limited slopes are dominated by erosion and weathering (denudation). On these slopes, processes such as rockfalls dominate and do not produce much debris that makes a slope gentler, but rather steeper.
Endogenic Factors
Rock Type
Hard resistant rocks often give steep escarpments whereas soft rocks such as sandstones are weathered easily producing gentler slopes.
Weathering
Weathering on slopes is most dominate and noticeable on free faces (scarps). Most physical weathering often produces fractures and granules along steep slopes maintaining their steepness. Chemical weathering is able to decompose slopes, e.g limestone making them gentler with time.
Soil Type
Cohesive soils such as clay are more closely packed and resist movement thus create steep slopes.
Incohesive sandy soils are widely spaced therefore are more susceptible to movement and erosion which produce gentler slopes.
Geological Structure
Uplift mechanisms such as folds or faults determine slope form. Faulting results in the formation of steep escarpments.
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