Dr Stefan Krause, Keele University, [email protected] C-Change in GEES: Human Pressures on...
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Dr Stefan Krause, Keele University, [email protected] C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion C-Change in GEES Human Pressures on the Environment Session 2 Session 2: Mass Movement, Weathering and Erosion
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Transcript of Dr Stefan Krause, Keele University, [email protected] C-Change in GEES: Human Pressures on...
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
C-Change in GEES
Human Pressures on the Environment
Session 2Session 2: Mass Movement, Weathering and Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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These slides were last updated in December 2009
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
DisclaimerLinks within this presentation may lead to other sites. These are provided for convenience only. We do not sponsor, endorse or otherwise approve of any information or statements appearing in those sites. The author is not responsible for the availability of, or the content located on or through, any such external site. While every effort and care has been taken in preparing the content of this presentation, the author disclaims all warranties, expressed or implied, as to the accuracy of the information in any of the content. The author also (to the extent permitted by law) shall not be liable for any losses or damages arising from the use of, or reliance on, the information. The author is also not liable for any losses or damages arising from the use of, or reliance on sites linked to this site, or the internet generally.Pictures, photographs and diagrams within this presentation have been produced by the author unless otherwise stipulatedNo content within this resource is knowingly an infringement of copyright. Any infringement can be immediately rectified on notification of the author of the resource
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Session Outline
• The Fundamentals of Erosion
• Causes of Erosion
• Management of Erosion (Agriculture)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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
Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Material:• Weathered• Transportable
Mode of transport:• Water• Wind• Gravity
Fundamentals of Erosion
Geological exfoliation of granite dome rock in the Enchanted Rock State Natural Area, Texas, USA.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
A prerequisite to erosion – produces the material for transportation
Chemical weathering
DissolutionHydration
Hydrolysis OxidationBiological
Carbonation
Physical and Chemical Weathering
Physical (mechanical) weathering
Thermal expansion Freeze thaw weathering
Pressure release Hydraulic action
Salt-crystal growth (haloclasty)Biological Weathering
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Carbonation
CO2 + H2O → H2CO3
(carbonic acid)
H2CO3 + CaCO3 → Ca(HCO3)2
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)
2NO2 + H2O → HNO2 + HNO3
(nitric acid)
2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4
(sulphuric acid)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
CaCO3 + 2H+ + SO42- → CaSO4 + CO2 + H2O
CaCO3 + 2H+ + 2NO3- → Ca(NO3)2 + CO2 + H2O
Chemical Weathering
• In aqueous solution, the acid dissociates into a H+ cation and a conjugate anion
• Nucleophilic anion replaces the carbonate
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
• 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
Chemical Weathering
Fe2SiO4 + 2H2CO3 + 2H2O → 2Fe2+ + 2OH- + H4SiO4 + 2HCO3-
4Fe2+ + 8HCO3
- + O2 + 4H2O → 2Fe2O3 + 8H2CO3
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Processes by which weathered material is transported
• Gravity erosion
• Water erosion
• Wind erosion
• Ice erosion
Transport
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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)
Gravity Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Solifluction:• Soil flow as a slow downslope
movement of water-saturated debris • 0.9 cm yr-1 on gentle slopes, 12-25
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.
Gravity ErosionSurface Creeping
Solifluction slopes in Alaska
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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
Water ErosionSplash Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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
Water Erosion FormsSheet Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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.
Water Erosion FormsRill Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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.
Water Erosion FormsChannel/Gully Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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
Wind Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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.
Wind Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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).
Wind ErosionThe Dust Bowl Disaster
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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 activitieswhich 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
Causes of Erosion
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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.
Climatic Factors
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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.
Vegetation
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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.
Soil Characteristics
USDA
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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.
Slope Characteristics
Waltham, T., (2009) Foundations of Engineering Geology. 3rd edition, Spon:
London.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and 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
Physical Impacts of Erosion
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, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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.
On Site Damages
Aerial photograph showing the delivery of sediment by the River
Rhône into Lake Geneva
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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
Off Site Damages
Eutrophication in the Caspian Sea
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
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
Erosion Management
Dr Stefan Krause, Keele University, [email protected]
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, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Erosion Management: Agriculture
http://www.uwsp.edu/geo/faculty/ozsvath/images/contour_plowing.htm http://www.rolybrown.ca/gallery2/d/1238-2/IMG_0788.jpg
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, [email protected]
C-Change in GEES: Human Pressures on the Environment – Mass Movement, Weathering and Erosion
Erosion Management: Agriculture
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, [email protected]
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
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 (http://creativecommons.org/licenses/by-nc-sa/2.0/uk/).
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Author Dr Stefan Krause
Stephen Whitfield
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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