Please enable JavaScript.
Coggle requires JavaScript to display documents.
Human causes of slope instability - Coggle Diagram
Human causes of slope instability
Deforestation
Decreases interception rate - less interception loss leading to a greater amount of water reaching the soil
Soil is less consolidated as roots bind the soil together increasing the cohesion of the soil particles
Less evapotranspiration - more water remains in the soil making it more likely to reach saturation
The exposed surface leads to greater erosion of the topsoil with rainwash and sheetwash
65% of deforestation in the Amazon is for cattle ranching
Urbanisation
A result of massively expanding settlements causing construction on marginal land (land that would be illegal to build on in advanced countries due to the instability) e.g. in Lima, Rio de Janeiro and Hong Kong Many favels and other hoomes being built on these hillsides ladds weight and makes the slopes less stable
Rio de Jainero has a hot and wet climate leading to fast chemical weathering. Bedrock is quickly broken down into deep regolith. The frequent heavy rains saturate the regolith so it flows over the underlying rock. 6.7 million people live there - 65% of growth is rural-urban migration.
7.5 million people live in Hong Kong (a growing figure). All the flat land has been used, so any further growth is on reclaimed land (on the sea), steep hillsides or pulling down buildings and putting taller ones there
Mining and extraction (undercutting)
A particular problem with mining is where to put the material not used e.g. 80% of the kaolin that is extracted is not used. Waste dumping into waste tips occurs overloading the slope.
Aberfan 1966, the coal waste from the local mine was stored in waste tips high above the town on the steep valley sides - at slopes of 25 degress over 200m above the town and unkowingly on a line of springs. In 1966, follwoing a night of heavy rainfall the soil became saturated and slope failure caused the waste material to liquify and flow downhill.
Increase in fossil fuels = more CO2 and therefore carbonation leading to more acid rain, causing more weathering. More global warming also causes more extreme weather events such as heavy precipitation.
Transport - roads to and from the mine promote deforestation = more easily saturated ground & more surface runoff
Undercutting - tunnels and shafts reduce the internal stability of slopes
Flooding- releasing material into local streams causing siliting and more likely flooding.
Acidification - increased emissions of sulphur dioxide (fossil fuels) = more sulphuric acid. This kind of weather rocks, more quickly, eroding the slopes.
Recreation
Coastal slopes can have big problems, especially as resorts are built as close to the sea as possible. Cliff slopes are especially susceptible to collapse as large amounts of basal undercutting occurs by the sea and process such as pressure dilatation means that pseudo bedding planes and vertical joints expand weakening the rock.
1993 was particularly wet, following a period of dry summers. The top layer lf the cliff became saturated and moved slow,y downhill taking Holbeck Halll Hotel with it.
Farming (ploughing)
Terracing can be used to stabilise slopes if done effectively. However generally, farming involving ploughing and terracing weakens the slope by creating steeper sections and removing larger plants which bind the soil toehthr.