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EARTH SURFACE PROCESSES Questions for thought * Define weathering and list the two main types. * What are the three main types of mass wasting, as categorised in the sources? * List five factors that can influence slope stability * Explain how water contributes to both physical and chemical weathering processes. * Compare and contrast soil-mantled threshold slopes and bedrock threshold slopes in terms of how they respond to changes in rock uplift rates. Introduction * Exogenic processes are those that operate on the Earth's surface. * They are driven by external forces such as climate, water, and biological activities. + These processes are responsible for the breakdown, transport, and deposition of Earth materials, shaping the landforms we see. * Examples: weathering, erosion, mass wasting. 12/9/2 12/9/2025 Y ResEcogenic processes: occur at the earth “surface Denudation/Degradation * These are the processes by which the landscape or land surface is destroyed. They include; * Weathering, * Mass wasting * Erosion. ceosn ncooe:reocanes sean pagh sanaens regener ot. Slopes Fundamental landscape elements, defined by their gradient or steepness, and constantly evolving due to various geomorphic Processes, : Slope processes are not just limited to mass movement. While ‘ mass movements, such as landslides, rockfalls, and debris flows, are.significant slope processes, other mechanisms Cantribute to the shaping and evolution of slopes. importance: * Understanding slope processes is crucial for predictin and mitigating natural hazards, sustainably mai land and water resources, and reconstructing past environmen Types of Slope Processes + Mass Movement Processes: These processes involve the downslope movement of material under the influence of gravity. + Fluvial Processes: These processes involve the action of flowing water on slopes. + Weathering weakens the material, making it more susceptible to erosion and mass movement. failure, Precipitation: Heavy rainfalt’ “Temperature: Freeze-thaw can trigger tandatides and cycles can weaken rock and debris flows, soit. Human Activities Excavation and loading Deforestation reduces Alterations to dtainage Increases stope stress: atabittiy Patterns: “without significant due to stress retlef 08 ‘chemicat iteration of overtying rock is lis minerals, Dominant in arid oF ‘cold climates. eroded away. ] —fhysical weathering Processes Salt crystal growth Dry/Arid Cumate intense heating and cooling set up internat stress 33 Exfoliation ‘dration Allregions ‘Airegions Rock tayers peel off in layers “The resui of hydration ie @ substance with water molecules incorporated ino its structure. This process ia often reversible, | Roots and burrowing animals ccororenooemocestsraaenarcheag | men quscoe vo 14 Hydrolysis ‘Carbonation Chelation tamaoas Rocks it operates in ‘oxygen + ‘Tron bearing rocks: elements in rocks Hydrogen in Silicate and Feldspar bearing rocks water+minerals Carbon dioxide+ Water Carbonate rocks Calcium, feldspar- mica and iron rich rocks Involves weak acids like humic and fulvic acid 6x00 :0cenc PROCESSES PREMRELSY ORM S ee 4 ar 4 Types of Weathering Contd. Biological weathering: The process of weathering induced by biophysical or biochemical agents confined within the upper few meters of the earth crust where plants roots are active. They may involve roots (which physically wedge rocks), lichens i.E. Algae, fungi (remove minerals and weaken rocks) and burrowing animals. (0€0 90 ©x00NC PROCESSES PREPARED RuAQUNCOE an) 15 16 12/9/2037 Environmental Factors Climate: Climate plays a crucial role indetermining the dominant weathering processes. Warm, humid climates favor chemical weathering, while cold, arid climates promote physical weathering. Hydrological Conditions: The amount Biological Conditions/Topography: Slope angle and aspect influence ex to weathering agents like suntight, rainfall, and wind. Rate and Extent of Weathering Depends on..... Rock Material Properties: Mineralogy: The composition ofthe Jointing and Fracture Spacing: joints rock determines its susceptibility to _and fractures provide pathways for different weathering processes. water and weathering agents (o Minerals like quartz are highly penetrate the rock mass, increasing resistant to weathering, while the surface area expored } feldspars ana mafic minerals are weathering. = more readily weathered. Grain Size: Fine-grained rocks tend to weather more rapidly than coarse- grained rocks due to their greater surface area. Stress Conditions: Stress release due to unloading can cause fracturing, enhancing weathering Porosity and Permeability: These properties influence the access of ‘water and other weathering agents to the rock mass. 18 “Slopes Maintain a condition of dynamic equilibrium, which means that material on a slope stays in place until one or another counterbalancing factor causes the slope system to readjust into a new state of equilibrium (of0 201 exocemic By Hg) ‘02s MRA GUCOE TZ ae Slope processes and Mass Movement = ope processes operating on ditierent parts of the slope id moisture content. + Water, vibrat dynamic equil downslope. and additional fe rium, Overcoming fi materials to overcome the frictional resistance and move ions and slope processes Contd.. Y +The angie of repose is the maximum slope angle that allows rock, sand, clay, and debris to stay in place without movement. The angle of repose depends on the slope material as well as its ing debris also shift the ion and allowing the slope (6£0 201 EX0GENC PROCESSES PREPAREELBY DR ) "MUA QUACOE ee) ¥ 19 20 Categories Flow Mass Movement - eliforsteep slope. Sides dccurwhen @ —Rotationatstides, Planarsldes involve Coherentmasso! —involvemovement movement along @ Matera moves alongacutved allure lator gently cpping downslope alonga surface; surtace, distinct fallure sure Flows involve the Debris flows are rapid Earth flows and movement of flows of water- mudflows: These material asaviscous saturated debris flows involve the fluid, down achannelor movement of finer: slope. They are often grained material, triggered byintense such as soll and clay. fainfallandcan be highly destructive. “Falisinvolvethe —_-Rooktlis ae “detachment and free common in areas fallof materiatfroma with steep, rocky slopes. They involve the detachment and © freefall of ck fragments from a clit stoat slob Sediment flows mostly are submarine environments elated: they are often triggered by earthquakes ot other disturbances. 25 12/9/2 Factors Affecting Mass Movement Several factors contribute to mass movement, including: * Slope angle: Steeper slopes are more prone to mass wasting, * Material properties: Loose, unconsolidated sediment is more susceptible to failure than solid bedrock, * Water content: Water saturati the likelihood of slope failure, ‘ Mi (on: Plant roots help bind soil, and vegetation intercepts rainfall, re ci ration and erosion. Deforestation can increase mass wasting susceptibility * Earthquakes: Seismic activity can trigger widespread landslides, es: Construction, road buildin ty itrigation can alter slopes i ion adds weight and reduces friction, increasing and drainage patterns, contributing to instabi 26 
