3. Rocks and Weathering Flashcards
9696 - Cambridge AS Geography
Plate Tectonics
The theory that Earth’s lithosphere (upper mantle and crust) is divided into rigid plates that move horizontally across the plastic asthenosphere below.
Size and Composition of Plates
Plates vary in size and are composed of continental crust (silica-rich) and oceanic crust (basalt-rich).
Movement of Plates
Plates move slowly (a few centimeters per year) in different directions, driven by mantle convection currents.
Global Patterns of Plate Movement
Seven major plates and numerous smaller plates make up the Earth’s surface, with distinct boundaries.
Divergent (Constructive) Boundaries
Plates move apart, allowing upwelling of mantle material to form new oceanic crust.
Key Features of Constructive Plate Boundaries
Mid-ocean ridges, volcanic activity, and rift valleys.
Conservative Boundaries
Plates slide past each other horizontally, creating friction and potential earthquakes.
Key Features of Conservative Plate Boundaries
Transform faults and mountain ranges.
Convergent (Destructive) Boundaries
Plates collide, pushing one plate under the other (subduction).
Subduction Zone Characteristics
Oceanic crust dives under continental crust or another oceanic plate, causing earthquakes, volcanic activity, and trench formation.
Seafloor Spreading
Molten rock rises at divergent boundaries, solidifying and creating new ocean floor, pushing continents apart.
Subduction
Oceanic crust sinks beneath another plate, recycling crust back into the mantle and creating deep ocean trenches.
Landforms of Subduction
Ocean trenches, volcanic island arcs (e.g., Japan).
Fold Mountain Building
Convergence can crumple and fold sediments at plate boundaries, forming mountain ranges.
Examples of Fold Mountains
The Himalayas, Alps, and Appalachians are all examples of fold mountains.
Ocean Ridges
Long, underwater mountain ranges marking divergent boundaries with volcanic activity.
Ocean Trenches
Deep, elongated depressions in the ocean floor marking convergent boundaries (subduction zones).
Volcanic Island Arcs
Chains of volcanic islands formed due to subduction, often parallel to trenches.
Weathering
The breakdown and decomposition of rocks and minerals at the Earth’s surface by physical, chemical, and biological processes.
Freeze-Thaw
Water expands as it freezes, causing cracks and fissures in rocks. Repeated freezing and thawing can break rocks apart.
Heating/Cooling
Repeated cycles of heating and cooling can cause rocks to expand and contract, weakening them and making them more susceptible to further weathering.
Salt Crystal Growth
Dissolving salts can crystallize within rock cracks, exerting pressure and causing the rock to crumble. This is common in arid environments.
Pressure Release (Dilatation)
As rocks are eroded and exposed to the surface, the pressure they were under is released. This pressure release can cause them to expand and crack.
Vegetation Root Action
Growing plant roots can exert pressure on rocks, wedging them apart and breaking them into smaller pieces.
Hydrolysis
Water reacts with minerals in rocks, breaking down their chemical structure and forming new compounds.
Hydration
Minerals absorb water molecules, expanding and weakening the rock structure.
Carbonation
Rainwater containing dissolved carbon dioxide becomes carbonic acid, which dissolves minerals like calcite (calcium carbonate) in limestone and creates new soluble compounds.
Climate’s affect on weathering
Temperature and precipitation play a major role. Warmer and wetter climates generally experience faster weathering rates.
Rock Type’s affect on weathering
Different rock types have varying susceptibility to weathering. For instance, porous rocks weather more easily than non-porous ones.
Rock Structure’s affect on weathering
Joints, cracks, and faults in rocks provide more surface area for weathering processes to attack.
Vegetation’s affect on weathering
Vegetation cover can protect rocks from physical weathering but can also promote chemical weathering through the production of organic acids.
Relief’s affect on weathering
Steeper slopes experience faster weathering due to increased exposure to water, wind, and gravity.
Peltier Diagram
A graphical representation showing the relationship between temperature and precipitation, and their influence on the dominant weathering processes.
High Temperatures and Low Rainfall Weathering Type
Chemical weathering dominates in hot, dry climates, with processes like carbonation being most effective.
Low Temperatures and High Rainfall Weathering Type
Physical weathering dominates in cold, wet climates, with processes like freeze-thaw being most effective.
Intermediate Temperatures and Rainfall Weathering Type
Both physical and chemical weathering processes can occur at moderate temperatures and precipitation levels.
Slope Processes
The natural movements of rock, soil, and other debris down a slope due to gravity.
Mass Movement
The downslope movement of a large mass of soil or rock under the influence of gravity.
Heaves
Upward or outward movement of the ground surface, often caused by swelling clays or frost action.
Flows
Rapid downslope movement of a saturated mass of soil or rock, like mudflows or debris flows.
Slides
Downward movement of a relatively coherent mass of soil or rock along a defined surface. Types include rotational slides (circular) and translational slides (planar).
Falls
Freefall of rock or debris from a steep slope or cliff, with minimal downslope movement.
Steep Slope’s affect on mass movement
Steeper slopes are more susceptible to mass movement due to increased gravitational pull.
Heavy Rainfall’s affect on mass movement
Water saturation weakens soil cohesion and increases weight, promoting instability.
Loss of Vegetation’s affect on mass movement
Vegetation helps bind soil particles together and reduces surface water runoff. Loss of vegetation increases the risk of mass movement.
Presence of Weak Layers’s affect on mass movement
Layers of loose material within the slope can act as slip surfaces for slides.
Seismic Activity’s affect on mass movement
Earthquakes can trigger mass movement by shaking slopes and disturbing their stability.
Loss of Life and Property as a result of mass movement
Large-scale mass movements can cause significant damage to infrastructure and endanger lives.
Landscape Modification as a result of mass movement
Mass movement reshapes slopes, creating features like landslides scars, debris deposits, and new landforms.
Rainsplash
Detachment and upslope movement of soil particles due to the impact of raindrops.
Surface Runoff
Flow of water downslope across the surface after rainfall
Sheetwash
Thin, widespread flow of water washing away a thin layer of soil.
Rills
Concentrated flow of water in small channels, eroding narrow grooves into the slope.
Soil Erosion
Removal of soil particles by water runoff, leading to land degradation and reduced fertility.
Gully Development
Rills can deepen and widen into gullies, creating deep channels on slopes.
Human Impact on Slope Stability
Human activities can both increase and decrease the stability of slopes.
Deforestation
Removal of vegetation reduces root structures that bind soil particles and increases surface runoff, leading to erosion and slope instability.
Slope Modification
Construction activities like road building, quarrying, and creation of steep building sites can alter slope angles and remove support structures, increasing the risk of mass movement.
Overloading
Placing heavy structures or overloading slopes with waste materials can exceed their carrying capacity and trigger instability.
Irrigation Practices
Excessive irrigation or leaky pipes can saturate slopes, weakening soil cohesion and increasing the risk of landslides.
Pinning
Insertion of metal rods or pins into the slope to reinforce weak zones and prevent movement.
Netting
High-strength netting applied to the slope face to trap falling debris and prevent further erosion.
Grading
Reshaping the slope to a gentler angle to reduce the gravitational pull acting on the material.
Afforestation
Planting trees and vegetation on bare slopes to bind soil particles, reduce surface runoff, and improve slope stability.
Prevention
Identifying areas at risk and implementing preventative measures is more effective and less costly than dealing with landslides after they occur.
Land-Use Planning
Avoiding development on steep slopes or areas prone to landslides.
Drainage Control
Diverting surface water runoff away from slopes through ditches, channels, or proper drainage systems.
Retaining Walls
Constructing walls to support slopes and prevent them from collapsing.
Early Warning Systems
Installing monitoring systems to detect early signs of instability and allow for evacuation if necessary.
Cause of Decreased Slope Stability in The Alps
Human activities in the Alps have contributed to a decline in slope stability.
Effect of Ski Resort Development on The Alps
Extensive development of ski resorts has involved deforestation for ski runs and infrastructure construction. Reduced tree cover weakens the stabilizing effect of roots and increases surface runoff, leading to soil erosion and steeper slopes.
Infrastructure Development
Building roads, railways, and other transportation networks often requires cutting into mountainsides, altering natural drainage patterns, and potentially creating unstable slopes.
Impacts of Mass Movement on The Alps
Unstable slopes in the Alps pose a significant threat to life, property, and the natural environment.
Loss of Life and Property in The Alps
Avalanches and landslides can destroy buildings, disrupt transportation networks, and cause fatalities.
Disruption of Natural Processes in The Alps
Mass movements can alter river courses, damage natural ecosystems, and contribute to increased sediment loads in waterways.
Strategies for Mitigating Risk in The Alps
A multi-pronged approach is needed to reduce the risk of mass movements in the Alps.
Improved Land-Use Planning in the Alps
Identifying areas at risk for landslides and avalanches and restricting development in those zones can significantly reduce the risk of disasters. Several Alpine countries have implemented stricter regulations for construction in high-risk areas.
Reforestation and Slope Stabilization in The Alps
Reforestation efforts and bioengineering techniques like planting shrubs and using natural materials to reinforce slopes can improve soil stability and prevent erosion. Austria, for instance, has projects underway to replant trees on slopes affected by ski resort development.
Early Warning Systems in The Alps
Installing monitoring systems that track weather patterns, slope movement, and snow accumulation can provide early warnings of potential avalanches and landslides, allowing for evacuations. Many Alpine regions have implemented sophisticated early warning systems to monitor slope stability.
