Sand and mud may seem like innocuous enough substances, and landslides and mudslides less dramatic-sounding than hurricanes and tsunamis. But this kind of natural disaster can be deadly.
What are landslides and mudslides?
A landslide is when a mass of soil, rocks and other debris moves down a slope, powered by the force of gravity. Sometimes, this movement is so sudden and rapid that it causes devastating loss of life and structural damage.
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A mudslide or mudflow is a type of landslide that contains a high water content. Mudslides are essentially ‘rivers of mud’ that vary in consistency from watery to thick, rock-laden mud that may carry large objects like boulders, bushes and trees along with them.
What causes landslides and mudslides?
Landslides and mudslides usually start on steep, eroded slopes during or after periods of heavy rainfall or rapid snow melt, when the soil becomes saturated. Alternate freezing and thawing may contribute to slope instability. Earthquakes and volcanic activity can also sometimes trigger landslides.
Meddling with the environment raises the risk for mudslides and landslides. Short-sighted development, for example where roads are cut into slopes or buildings are allowed to encroach too high on hill-sides, can further destabilize the soil. Erosion of slopes, caused by factors such as over-grazing or fires, also renders them vulnerable. Areas that have lost vegetation to repeated wildfires (such as the slopes of Table Mountain) are often prone to this problem, especially after rainfall.
Human-induced climate change, with its associated greater weather extremes, is also thought to be responsible for weakening vulnerable slopes in several landslide-prone areas.
Risks from landslides
The immediate risk to human life from a landslide or mudslide is being caught in its path: sand, and thick mud especially, can cause suffocation, and people can be trapped or crushed by boulders or other debris, or by buildings collapsing under the weight of the flow.
Landslides can also disrupt power lines and water and sewerage pipes, potentially leading to electric shock and contaminated drinking-water. Roads and other transportation arteries may be blocked by debris, raising the risk for accidents and hampering access by rescue and medical services.
How to avoid them
The United States Federal Emergency Management Agency has the following suggestions for surviving a landslide:
Be in tune with your surroundings. If you’re travelling to a new area, swot up on it and find out about the potential risks (landslides or otherwise). Check out the topography: are there dodgy-looking slopes (steep or eroded) in the area? And especially: what is the weather doing? Intense rainstorms can be dangerous, especially if there’s been a preceding period of wet weather.
If you decide not to leave the area, then at least stay awake if you think there’s a chance of a landslide: many such disasters have occurred while their victims were asleep. Keep a portable, battery-powered radio with you to stay in touch with any safety announcements. Move up to a second storey if possible, which might help to keep you above the level of the debris.
Listen for unusual sounds that might indicate moving debris, such as tree branches breaking, boulders knocking, or a faint rumbling that increases in volume.
A trickle of mud or soil may precede the main landslide. If you are near a stream or channel, beware of a sudden increase or decrease in water flow, or a change from clear to muddy water: this could mean landslide activity upstream. If you’re driving, remember that road embankments are prone to landslides. Also watch out for fallen rocks and mud.
Any of the above signs mean you may have only a few minutes (or even seconds) to get out of the path of the landslide.
Also, beware if the following occur for the first time:
Cracks in walls or the ground.
Doors or windows stick.
Outside walls or stairs lean away from the main building.
Underground utility lines break.
The ground bulges at the base of a slope.
Water breaks through the ground surface.
Fences, walls, utility poles or trees tilt.
If you’re caught in their path
If you’re indoors when a landslide hits, stay there and get under a strong piece of furniture like a sturdy desk.
If you’re outside, run to the nearest high ground in a direction away from the path of the landslide. Or at least get behind something that might afford you protection from rocks and other debris, like a stand of trees or a building.
Failing that, curl into a ball and wrap your arms round your head to protect it.
- Olivia Rose-Innes, EnviroHealth Expert, Health24, updated November 2006
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