Landslide Risk Assessment

A landslide is the down-slope movement of soil, rock and organic material due to gravity, along with the resulting landform (Dai et al, 2002).

British Columbia experiences significant losses each year due to earthquakes. The province’s steep, mountainous topography combined with high precipitation and unconsolidated glacial sediments make it particularly susceptible to landslide activity (BC Government, 2010).  The continued expansion of human development has caused landslide risk to increase, and the threat of these hazards needs to be better evaluated in order to prevent fatalities and property damage.

Landslide on Sea to Sky Highway. Source: Landslide Blog

Areas susceptible to landslides combine one or more of these factors:

• Weak underlying bedrock or soil

• Steep slope geometry and weak slope configuration

• Unstable ground water conditions  
• Vegetation with poor stabilizing ability

 
The initial slope failure can be triggered by:

• Gradual processes such as weathering
• Intense or prolonged rainfall or rapid snowmelt

• Loading on upper slopes

• Human activity (such as road building, irrigation, deforestation)

The aim of this project is to assess these different risk factors using GIS technology. By layering slope, precipitation, vegetation, soil type, river, road, and population data, we were able to assess the areas most at risk for landslides on Vancouver Island. These factors were chosen since  Vancouver Island's Insular Mountains are most susceptible to debris flows, which occur on soil due to intense precipitation (The Atlas of Canada, 2009).