Landslides & Debris Flows

Landslides include a range of downhill earth movements, including slope failure, rock falls and debris flows. Landslides can be extremely destructive and are caused by a number of pre-existing and contributing factors that cause the slope to fail, including heavy rainfall or rapid snowmelt, erosion, poor construction practices, freezing and thawing, earthquakes and volcanic eruptions. 

Debris flows are fast-moving liquefied landslides that carry tonnes of soil and other debris like gigantic boulders. Debris flows are most often caused triggered during periods of intensive rainfall that follow prolonged rainfall which results in water saturated soil. 

Concave slopes like gullies and ravines are particularly susceptible to debris flows because they tend to concentrate surface water runoff and accumulate surface water and loose soil. Debris flows can be initiated due to both natural factors and man-made intervention.

Before:

  • Develop a household emergency plan and assign specific safety tasks to family members. Practice your household emergency plan every six months.
  • Put together an emergency kit to be self-sufficient for at least 72 hours, but aim for one week. Keep a kit in your vehicle, and at school or work.
  • Plan a family meeting spot and have an contact, such as a family member in another region, to check in with if you become separated.
  • Get training in emergency preparedness and first aid.
  • Keep your vehicle in working order and always have at least half a tank of gas.
  • Pay attention to notices of danger and information updates on radio, TV and the internet.
  • If you live on or under a steep slope, ensure that you meet bylaw requirements and consult a professional if you are concerned about slope stability on your property. Contact your local government if the slope of concern is on public property.
  • Be familiar with the debris flow hazard and risk associated with your property and understand the debris flow warning classification.
  • Design, landscape, and reinforce your property so that it mitigates landslide risk.  Ensure there is a proper drainage system in place, drain water away from steep slopes, and do not undercut a slope without professional consultation.

During:

Immediately evacuate the building you occupy then dial 9-1-1 when you notice these signs of a debris flow:

  • Rapid water or slurry flow, where it has not been observed before;
  • Irregular or suddenly stopped stream flow;
  • Cracking or falling trees, particularly in the absence of strong winds.

If a warning has been issued, the best way to stay safe is to evacuate the premises that are in danger of being affected. The choice of whether or not to evacuate is up to the individual.

  • If you are evacuating, ensure that your planned route is intact, and use caution around known bodies of water and at night, as water and debris might impede your travel.
  • If the debris flow has already occurred and the building you are in is safe and intact, it may be best to wait for emergency responders especially if surrounded by flowing water, which could be a sign of a secondary debris flow.

After:

  • Stay away from the slide area as subsequent slides can occur.
  • If you suspect people have been trapped, direct rescuers to their location. Do not enter the direct slide area yourself. 
  • Help any neighbours who may require special assistance (i.e., infants, elderly people, and people with disabilities). 
  • ​Listen to local radio or television stations for the latest emergency information.
  • Watch for flooding, which may occur after a landslide or debris flow. 
  • Check for structural damage and report broken utility lines to appropriate authorities.
  • Restock any emergency supplies that you might have used.
  • Replant damaged ground as soon as possible to prevent erosion caused by loss of ground cover.
  • Seek the advice of a geotechnical expert for evaluating landslide hazards or designing corrective techniques to reduce landslide risk. A professional will be able to advise you of the best ways to prevent or reduce landslide risk, without creating further hazard.
  • One Step at a Time: A Guide to Disaster Recovery has further information on recovery activities.