3.4 The human impact Flashcards
What are some of the indirect human causes?
Acidification: oxides from industrial processes emit oxides which add to acid rain. It can acidify lakes, kill trees and accelerate weathering.
Weathering rates rise with climate change.
Mining for materials cause waste rock and pollution. It can decrease stability and saturation and so slope stability falls - especially if it leads to a steeper angle.
Deforestation increases saturation and thus weight. Tree rocks also hold material together
Ploughing and overgrazing can loosen slopes.
What are some of the direct human causes?
Mining - decrease in toe support due to undercutting, may be coastal
Dams: reservoir water seeps into hillsides and saturates them. Sedimentation and erosion also decrease stability.
Construction and loading - waste heaps increase load
Traffic vibrations from heavy vehicles can trigger mass movements
Stabilising slopes and coastal management
Soil heap and waste heaps
Excavation i.e. for roads can create steeper slopes - old slips may be reactivated if the toe is removed.
What are some strategies to reduce the impact of mass movements?
Pinning: drilling a hole in the stable rocks and inserting a metal rod and plate to anchor down the rock to prevent falls.
Netting: netting fastened to the rock face to prevent loose rocks and scree from falling on areas
Gabions: metal mesh boxed filled with rocks to stabilise the toe of landslip or alongside roads.
Drainage: excess water adds mass and lubrication. Draining water is key to prevent all mass movements and so drainage is often used. The cheapest way is to fill a trench with permeable gravel
Grading: reprofiling the slope to make it more stable. Slopes are made more gentle to become more stable. However, this leads to excavation and waste rock.
Afforestation: trees reduce soil erosion - reduced surface runoff and absorb water and less infiltrated water. The roots also bind soil together however can add weight to the slope.
Grouting: inject rocks with cement to reduce pore water and increase strength.
Shotcrete: spray loose rock surfaces with concrete to prevent loose blocks falling from the slope.
Mapping hazards: many mass movements occur on reactivated previous movements due to rainfall, earthquakes or excavation. Planners use this to decide where building should occur or management is needed. This is determined through historical records and topography.
