Explained: What causes landslides, can they be predicted?
Three consecutive landslides hit Kerala's Wayanad district on Tuesday morning. The landslides took place in hilly areas near Meppadi, wiping out much of Chooralmala village, destroying infrastructure, and killing at least 70 people. A hundred others are feared trapped under the debris, even as rescue operations continue. Let's try to understand how landslides occur and whether they can be predicted.
Why do landslides happen
Landslides happen when the pull from gravity exceeds the strength of the geomaterial forming the slope of a hill or mountain. Geomaterials can be as varied as rocks, sand, silt and clays. Then, part of this slope starts sliding downhill. Depending on where the slope fails, the material sliding down can be just a few cubic metres or a few million cubic metres in volume.
Why do slopes fail
Most natural landslides are triggered by earthquakes or rainfall, or a combination of both. Earthquakes shake the ground, stress it and weaken it over time. Rainwater can seep through the ground and soak it—the ground is often porous like a sponge—and add weight to the slope. Another adverse effect of water is erosion: the constant action of waves undercuts coastal slopes, causing them to fail. Groundwater can also dissolve rocks within slopes.
How do humans cause landslides
Humans can, and do, cause landslides in several ways, too. For example, deforestation has a negative impact on slope stability, as tree roots naturally reinforce the ground and drain water out. Unplanned infrastructure in hilly areas can also trigger landslides. Additionally, mine blasts produce small earthquake-like ground vibrations that shake slopes nearby.
Difficult to mitigate landslide risk effectively
It's very difficult to predict and mitigate landslide risk effectively, according to the Conversation. To accurately assess the stability of the slope, a three-dimensional mapping of these materials and their strengths is needed. No sensor can provide this information, so geologists and geotechnical engineers must deal with partial information obtained at a few selected locations and extrapolate this data to the rest of the slope. The question of "when will a landslide will occur" is also uncertain, the Conversation added.
Landslides wreak havoc on infrastructure
In Kerala, the landslides struck between 2:00am and 6:00am obliterating a section of Chooralmala town including shops and vehicles. Local residents reported that over 200 houses were washed away in the disaster. The National Disaster Response Force (NDRF), State Disaster Response Force (SDRF), fire brigade, police, and local emergency response teams are engaged in rescue operations. According to reports, rescue efforts were affected after a bridge over Iruvazhinji River that connected Chooralmala and Mundakkai villages collapsed.
Indian Army called in to assist, more rain predicted
Meanwhile, the Indian Army from Wellington, Coonoor has been summoned to assist with the rescue operation and construct a temporary bridge to reach Mundakkai. State Forest Minister AK Saseendran confirmed that "the situation is serious" and all agencies have been pressed into service. He added that more rain is likely to the day. The Hume Centre for Ecology and Wildlife Biology reported more than 300mm of rain at many locations along the Western Ghats in the past 24 hours.
