Dr Stefan Krause, Keele University,

Name: Dr Stefan Krause, Keele University,
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Description: Dr Stefan Krause, Keele University,

Dr Stefan Krause, Keele University, s.krause@esci.keele.ac.uk
C-Change in GEES Human Pressures on the Environment Session 2: Mass Movement, Weathering and Erosion Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

How to use the teaching slides These slides are not intended to form a complete lecture on the session topic. These resources are designed to suggest a framework to help tutors develop their own lecture material The resource slides comprise where appropriate; key points, case studies, images, references and further resources. There are limited case studies included. Students can develop their own portfolio of case studies as part of coursework activities These resources may be used for educational purposes only, for other uses please contact the author These slides were last updated in December 2009 Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

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Session Outline The Fundamentals of Erosion Causes of Erosion Management of Erosion (Agriculture) Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Erosion Displacement / down-slope transport (exception biogenic erosion) of particles, solid material (sediments, rock, mud, soil, snow, dust) Transport following gravity or by agents such as, wind, water, ice Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Fundamentals of Erosion
Material: Weathered Transportable Mode of transport: Water Wind Gravity Geological exfoliation of granite dome rock in the Enchanted Rock State Natural Area, Texas, USA. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Physical and Chemical Weathering
A prerequisite to erosion – produces the material for transportation Physical (mechanical) weathering Thermal expansion Freeze thaw weathering Pressure release Hydraulic action Salt-crystal growth (haloclasty) Biological Weathering Chemical weathering Dissolution Hydration Hydrolysis Oxidation Biological Carbonation Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Chemical Weathering Change in the composition and form of rocks through chemical reaction Carbonation: atmospheric carbon dioxide is dissolved in rainwater to create carbonic acid, which reacts with calcium carbonate Other gases also dissolve in water to produce acid solutions which react with rock minerals (nitrous oxides → nitric acid) (sulphur dioxide → sulphur trioxide → sulphuric acid) Carbonation CO2 + H2O → H2CO3 (carbonic acid) H2CO3 + CaCO3 → Ca(HCO3)2 2NO2 + H2O → HNO2 + HNO3 (nitric acid) 2SO2 + O2 → 2SO3 SO3 + H2O → H2SO4 (sulphuric acid) Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Chemical Weathering CaCO3 + 2H+ + SO42- → CaSO4 + CO2 + H2O
In aqueous solution, the acid dissociates into a H+ cation and a conjugate anion Nucleophilic anion replaces the carbonate CaCO3 + 2H+ + SO42- → CaSO4 + CO2 + H2O CaCO3 + 2H+ + 2NO → Ca(NO3)2 + CO2 + H2O Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Chemical Weathering Hydrolysis is decomposition (usually of silicate minerals) in reaction with water Mg2SiO4 + 4H+ + 4OH- → 2Mg2+ + 4OH- + H4SiO Hydration is the addition of the entire water molecule to the mineral structure – commonly occurs in clays Oxidation is the bonding of oxygen, dissolved in surface water, to the metallic elements of the minerals Fe2SiO4 + 2H2CO3 + 2H2O → 2Fe2+ + 2OH- + H4SiO HCO3- 4Fe2+ + 8HCO3- + O2 + 4H2O → 2Fe2O3 + 8H2CO3 Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Transport Processes by which weathered material is transported Gravity erosion Water erosion Wind erosion Ice erosion Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Gravity Erosion Gravity-driven mass movement of rocks, sediments, soil Shear stress (exerted by weight of material under gravity) > Shear strength Gravity is the vertical component of a downslope force Importance of slope angle Sometimes very slow (e.g. surface creeping) Sometimes very fast (e.g. rockfall, landslides) Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Gravity Erosion Surface Creeping Solifluction: Soil flow as a slow downslope movement of water-saturated debris 0.9 cm yr-1 on gentle slopes, cm yr-1 on steeper slopes Gelifluction: Downslope flow of soil in association with ground ice Occurs in periglacial environments (no percolation of water because of the permafrost) After melting of ice, ice lenses provide lubricant to cause downslope flow. Solifluction slopes in Alaska Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Water Erosion Splash Erosion Detachment and airborne movement of small soil particles Caused by the impact of raindrops falling on open soil Initial precipitation fills pore spaces in the surface soil and loosens particles, subsequent rain drops hit loose particles and splash them away Raindrop dislodges soil particles, makes them more susceptible to movement by overland water flow Loosened particles that are not washed away can form a muddy slick that clogs pores in the ground surface Sealed surface further reduces infiltration and increases runoff Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Water Erosion Forms Sheet Erosion Removal of a uniform layer of soil from the land surface It is a result of rain splash followed by runoff Water moves as broad sheets over the land and is not confined to small depressions in the soil. Sheets of water carrying sediment particles can have substantial erosive force Potential for sheet erosion depends on: soil type, velocity, and quantity of flow over the surface Difficult to detect until it becomes rill erosion Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Water Erosion Forms Rill Erosion Development of small grooves spaced fairly uniformly along the slope Caused when runoff is heavy and water concentrates in rivulets Individual rills range in depth and width up to several inches and reflect a tremendous loss of soil If rilling is not corrected, it will develop into gullies. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Water Erosion Forms Channel/Gully Erosion
Occurs in both intermittent and permanent waterways and streams Three causes of channel erosion are: Increased runoff Removal of natural vegetation along the waterway Channel alterations resulting from construction activities It includes both stream bank and stream bed erosion. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Wind Erosion Soil moved by air - similar to water erosion Fine particles are moved easily, if as small as clay and silt, they can become airborne Sand particles between 0.1 and 1 mm move by saltating (jumping) over the ground, like a sheet. Heavier particles move by rolling. Unlike water, wind can move soil over very large distances of thousands of kilometres and over seas to other countries. It can move soil up-hill Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Wind Erosion Travel length dependent on particle size Finest clay particles are transported furthest – dust clouds – inter continental (Sahara sands in central Europe) The amount of soil moved must not be underestimated, and once in motion, and the air heavy with dust, its erosive power increases. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Wind Erosion The Dust Bowl Disaster During the 1930s, a prolonged period of low precipitation/drought culminated in dust storms and soil destruction of disastrous proportions. The "black blizzards" of the resulting Dust Bowl have been called the greatest US environmental disaster of the 20th century. A major reason for dust bowl development was the unsustainable development of agricultural practice in the Great Plains. Apart from the catastrophic environmental impact the economic implications were huge (loss of most fertile soil). Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Causes of Erosion Anthropogenic Impacts: Vibrations from machinery or traffic Blasting Earthwork altering the shape of a slope or imposing new loads on an existing slope Loss of slope stability by removal of vegetation, deep roots Construction, agricultural, or forestry activities which change the amount of water infiltrating into the soil (Semi) Natural causes: Erosion of the toe of a slope by rivers or ocean waves Weakening of a slope through saturation (snowmelt, glacier melt, rain) Earthquakes adding loads to barely-stable slopes Volcanic eruptions Groundwater pressure acting to destabilize the slope Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Climatic Factors Rainfall: Amount, intensity, and frequency – due to high soil moisture and saturated conditions during periods of frequent rainfall, a greater percentage of the rainfall will become runoff Temperature: Frozen soil is highly resistant to erosion, rapid thawing of the soil surface brought on by warm rains can lead to serious erosion. Erosion intensity dependent on type of precipitation – e.g. falling snow does not erode, however, heavy snow melts in the spring can cause considerable runoff damage. Influences the amount of organic matter that collects on the ground surface and incorporates with the topsoil layer. Organic matter protects the soil by shielding it from the impact of falling rain and soaking up rainfall that would otherwise become runoff. Warmer climates - thinner organic cover on the soil. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Vegetation Most important physical factor influencing soil erosion Vegetation cover shields the soil from the impact of raindrops, binds soil together, making it more resistant to runoff A vegetative cover stops wind erosions, provides organic matter, slows runoff, and filters sediment A dense, robust cover of vegetation is one of the best protections against soil erosion. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Soil Characteristics Erodibility influenced by texture (size or combination of sizes of the individual soil particles), structure and cohesion Silt rich soils are most susceptible to erosion from wind and water Clay or sand-sized particles are less prone to erosion. Structure influences both the ability of the soil to absorb water and its physical resistance to erosion. Cohesion refers to the binding force between soil particles and influences the structure. When moist, the individual soil particles in a cohesive soil cling together to form a doughy consistency. Clay soils are very cohesive, while sand soils are not. USDA Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Slope Characteristics
Slope length, steepness and roughness affect erodibility. Generally, the longer the slope, the greater the potential for erosion. The greatest erosion potential is at the base of the slope, where runoff velocity is greatest and runoff concentrates. Slope steepness, along with surface roughness, and the amount and intensity of rainfall control the speed at which runoff flows down a slope. The steeper the slope, the faster the water will flow. The faster it flows, the more likely it will cause erosion and increase sedimentation. Waltham, T., (2009) Foundations of Engineering Geology. 3rd edition, Spon: London. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Physical Impacts of Erosion
Damage from erosion and sediment results in loss of fertile top soil clogged ditches, culverts, and storm sewers that increase flooding muddy or turbid streams damaged plant and animal life filled-in ponds, lakes, and reservoirs damaged aquatic habitats and reduced recreational value and use structural damage to buildings, roads, and other structures Sediment-laden water pours into the northern Gulf of Mexico from the Atchafalaya River. Image taken by MODIS on NASA’s Aqua satellite. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

On Site Damages US: 4.5 billion tons of sediment pollution to the rivers each year This is the equivalent to a volume the size of 25,000 football fields, 100 feet high. It is estimated that 6-13 billion dollars per year are spent in the U.S. to correct the effects of erosion and sediment pollution. Aerial photograph showing the delivery of sediment by the River Rhône into Lake Geneva Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Off Site Damages Mainly by sediment inputs when the detached particles generated by erosion are deposited elsewhere on the land or in lakes, streams and wetlands Substantial sediment inputs from agricultural areas into freshwater systems cause eutrophication, oxygen stress and ecological deterioration Eutrophication in the Caspian Sea Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Erosion Management Riparian fencing: protecting slopes from cattle trampling – allows vegetation to regrow Shelter belts and grassed waterways : vegetation growth at field boundaries Spaced tree planting: roots hold soil and cycle nutrients Reduced tillage: tilling only the areas that matter while minimally disturbing the soil. Tilling between furrows. Stubble-mulching: leaving stubble on the field as long as possible to reduce evaporation and keep the soil covered. Stubble has to be mulched rather than ploughed. Contour ploughing: works a bit like terracing, preventing moisture from running down-hill and reducing erosion considerably. Terracing: extensively practised in padiculture – drastic erosion management measure Reduced compaction: using machinery and technology that spreads its weight over a larger area. Optimal fertilising: avoiding degradation of soil from over-fertilising Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Erosion Management: Agriculture
Stubble-mulching: leaving stubble on the field as long as possible to reduce evaporation and keep the soil covered – important for the prevention of wind erosion, particularly common in US Great Plains. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Contour ploughing: Ruts made by the plough run perpendicular rather than parallel to slopes. The rows formed slow water run-off during rainstorms to prevent soil erosion and allows the water time to settle into the soil. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Terraced land around Konso in Southern Ethiopia Terracing: This form of land use is prevalent in many countries, and is used for crops requiring a lot of water, such as rice. Terraces are also easier for both mechanical and manual sowing and harvesting than a steep slope would be. Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

Session Summary Erosion involves two processes: weathering and transport Climate (particularly precipitation) is an important factor in both - climate extremes increase erosion Problem of global scale, particularly in the context of growing population and food demand Agricultural methods can be employed to manage, and reduce the impact of, erosion Dr Stefan Krause, Keele University, C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion

This resource was created by the University of Keele and released as an open educational resource through the 'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography, Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE Academy UKOER programme and coordinated by the GEES Subject Centre. This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license ( However the resource, where specified below, contains other 3rd party materials under their own licenses. The licenses and attributions are outlined below: The name of the University of Keele and its logos are unregistered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license

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Institute – Owner Keele University, School of Physical and Geographical Sciences Title Mass Movement, Weathering and Erosion Powerpoint Presentation Date Created January 2010 Description Mass Movement, Weathering and Erosion – Powerpoint Presentation – Part Two of Human Pressures on the Environment Educational Level 1 Keywords (Primary keywords – UKOER & GEESOER) UKOER, GEESOER, Weathering, Erosion, Management Creative Commons License Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales

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