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Landslides

A landslide is the rapid mass movement of soil, mud and/or rocks downhill due to the pull of gravity. Landslides are very common and occur in a variety of forms. Land may topple off in a big chunk, or slip down in bits. Landslide may be composed of mud or may contain rocks and other debris. Most landslides occur gradually, but some may be sudden.

Natural causes of landslides include:
1) Heavy and/or prolonged rain
Gravity is an invisible force that pulls all objects towards Earth. The effect of gravity is more prominent on a steep slope or on a hilly area. When rain falls, water enters or infiltrates into the top soil which makes the soil become heavier and therefore more vulnerable to the pull of gravity. When soil absorbs all the water that it is capable of holding, it is said to be saturated. Soil is therefore heaviest and most susceptible to the effects of gravity, when saturated. When large areas of soil become saturated on steep slopes, the pull of gravity causes the top layers of the soil to slide downhill, therefore resulting in a landslide.

2) Tremors And Shakes
An Earthquake is a tremor or movement in the Earth’s crust. They are a deadly and unpredictable type of natural disaster and are the leading reason for landslides or Rock falls occurring worldwide. Loose soil, rocks and boulders can easily be dislodged from hilly areas and allowed to move downhill when the violent shaking of the ground transpires. Landslides are more likely to take place when the earthquake is of a high magnitude.
Human Induced Activities that produce landslides:

  1. Deforestation
  2. Quarrying/ Rock Mining
  3. Bad agricultural practices such as slash and burn agriculture

Deforestation is the removal or cutting down of trees and other types of vegetation from the land. The firm roots of the trees also help to keep the soil in place, even when it absorbs water, thus diminishing the effects that gravity has on the soil. It is when these trees are removed that the bare and exposed soil is left defenceless against the pulling force of gravity when saturated since trees help to keep soil firmly in place. Soil movement takes place more easily and rapidly resulting in deadly landslides.
Quarrying or rock mining refers to the cutting away or excavation of hilly or mountainous areas so that rocks and minerals can be extracted from the land. Quarrying is rampant in the Northern Range and results in the land being left devoid of trees and vegetation. Without trees to hold the soil in place, soil movement occurs easily and rapidly.

Before a Landslide:

  1. A ground assessment should be done of your property. When this is done you would know the kind of soil type that your property is built on, and would be able to determine how susceptible it would be to ground movements and if landslides are a possibility.
  2. Find out whether the area in which you live is prone to landslides. Landslides usually occur in the same areas, so if a landslide has occurred in your area it would mean that the chances of another landslide occurring in the future are high.
  3. If you live in a high risk area an evacuation plan should be prepared.
  4. Plant trees and other types of vegetation that would help to stabilize soil on the slopes of your property.
  5. Look for changes to your surroundings that may signal the likelihood of landslide activity, such as leaning fences or walls.
  6. When driving along routes on hilly areas, such as the roads to Maracas, drive with your windows down and without music. This should be done so that you would hear any unusual sounds such as the knocking together of rocks or the cracking of trees, which are warning signs of the possibility of a landslide occurring.
  7. Also while driving along those areas, if you see an abnormal amount of leaves from trees falling, it could be the signal that a landslide is about to occur.

 

During a landslide:

  1. If you are inside of a building, stay inside; don’t leave your home until it is officially safe to do so.
  2. If outdoors, try to get to the nearest high ground in the direction away from the path of the landslide.
  3. If you are at a river, be prepared to leave the area immediately if there are signs that a landslide has occurred higher upstream. Don’t try to take your belongings, just leave the area as fast as possible.
  4. If driving, remain alert and look out for collapsed pavements, mud and fallen rocks.

 

After a Landslide:

  1. Don’t go into or return to an area that just experienced a landslide since there may be additional landslides. Only return to the area once it is officially safe to do so.
  2. Flooding may occur after a landslide since they might be caused by the same factors.
  3. Provide assistance to neighbours and to any special needs individuals such as children and to the elderly.
  4. Check your property for any structural damage.
  5. Check for any damaged utility lines or ruptured water mains. Report any damage that may have occurred to the relevant utility company such as T&TEC and WASA.
  6. Replant damaged ground immediately since soil erosion could be further caused by loss of ground cover.

 

Tell- tale signs of an impending landslide:

  1. Doors or windows stick or jam for the first time;
  2. New cracks appear in plaster, tile, brick or foundations;
  3. Outside walls, walks or stairs begin pulling away from the building;
  4. Slowly developing, widening cracks appear on the ground or on paved areas such as streets or driveways;
  5. Underground utility lines break;
  6. Bulging ground appears at the base of a slope;
  7. Ground water seeps to the surface in new locations;
  8. Fences, retaining walls, utility poles or trees tilt or move;
  9. You hear a faint rumbling sound that increases in volume as the landslide nears. The ground slopes downward in one specific direction under your feet.
  10. If you are driving along a road (E.g. the North Coast Road) drive with your windows down and with no music; this is done so that any unusual loud sounds of an impending landslide could be heard.
  11. Also look out for an unusual amount of leaves from trees falling as this could be an indication that a landslide is about to occur.

 

What makes a person vulnerable to landslides?
Physical Vulnerability:

  1. Building on hilly areas or on slopes: These areas are considered to be most prone to landslides and building on hilly areas or on slopes increases ones chances of being negatively affected by landslides.
  2. Not building homes on the right foundation. A house may need to have a shallow or deep foundation depending on the type of soil and therefore the extent of soil movement of the area. Building on the right type of foundation would decrease the impact of soil movement on the structure.
  3. Building homes in areas that are traditionally known to be prone to landslides. Landslides usually occur in the same areas and constructing in an area that is known to be affected by landslides would increase ones vulnerability.
  4. Not using proper building codes, buildings that lack structural integrity are more susceptible to be damaged by a landslide than a more sturdy building.
  5. Buried pipelines, brittle pipes, burst water mains: Buried pipelines must be made from a flexible material so that they would shift with the soil movements and not be more prone to breaking when there’s soil movement.

Social Vulnerability:

  1. Family structure- Female headed households and households with a large number of dependencies are considered to be more vulnerable to the negative impacts of disasters.
  2. Illiteracy- Lack of education on the causes and mitigation measures that one can use to reduce the effects of flooding.
  3. Lack of personal safety- Some individuals have higher personal levels of acceptable risk and would therefore risk living in areas that are very prone to flooding.
  4. Special needs individuals such as the elderly and the mentally challenged would be more vulnerable to disasters.

Economic Vulnerability:

  1. Poverty
  2. Unemployment
  3. Debt

Environmental Vulnerability:

  1. Quarrying, this leaves the land barren and susceptible to soil movements.
  2. Deforestation
  3. Soil type found in the area: certain soil types are more prone to ground movement than others, therefore it’s always important to determine the soil type, it would give an indication of what type of foundation you would need to have to decrease the impact of soil movement.
     

How to reduce vulnerability:

  1. Conducting a soil analysis before constructing so that a suitable foundation can be made.
  2. Public education- public education initiatives would increase the populace awareness of the hazard and what they can do to mitigate against it. Such initiatives would make people better aware of the risks that they face, especially those that live in high risk areas.
  3. Build retaining walls in areas that are prone to landslides.
  4. Policies regarding the use of proper building codes when constructing structures should be enforced.
  5. Provide incentives and monetary help to special needs individuals so that they would have the finances to build more resilient homes.

Further Reading :

 

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