It always starts with breaking the ground of a slope – which, in turn, needs to be triggered by something. The most known causative agent is rain. But there are also others, such as earthquakes, volcanic eruptions and vibrations caused by machines.
Landslides are natural phenomena: they can occur even if the area’s vegetation is intact. But human action can facilitate its occurrence and increase strangers.
1) Saving plants
Deforestation of slopes and irregular occupations on hills are considered “risk factors” for landslides. First, because vegetation usually softens the impact of rain, as its roots help stabilize the soil.
But not every type of plant helps. Banana trees, for example, have weak roots and heavy trunks, which do a lot of damage when they fall. In addition, there is the “leverage effect”: when the wind shakes such a tree, its roots displace the earth and end up making the situation worse.
2) Downhill
The way the soil is organized also influences landslide – the more compact the soil, the safer it tends to be. Clay soils, therefore, have an advantage over sandy soils, as they form a more “full-bodied” mass.
Another factor that can make or break land is the slope. Most tragedies occur on slopes reclined at angles ranging between 20 and 35º.
Less than that, the risk of landslides decreases. More than that, a lot of land may even roll down the slope, but the number of victims will be much smaller – after all, the angle makes it difficult to build (and occupy) houses, roads, and other structures.
3) Obstacle race
Rain on sloping ground will always form channels through which water runs off – these are called “drainage networks”. They don’t need to be pipes or artificial gutters: nature itself is in charge of creating these «paths». In a case of slippage, however, these channels help to spread the problem.
Earth and debris fall into the net and can split through it, multiplying the devastation area and dragging materials to relatively distant regions.
4) Wrong addresses
No intervention makes the situation worse than irregular occupation. First, because the constructions are eliminating the vegetation cover of the area. Second, because the earth extracted to flatten the hill in the inhabited area is generally thrown down and becomes “loose”. Finally, because the villages created on the slopes create gaps, which can “channel” (and intensify) landslides.