Although residents and authorities say that Pettimudi in Idukki was a safe zone, geologists believe the region may have always been vulnerable to tremors.

Pettimudi Rajamala near Munnar in Idukki district in Kerala where 62 people died in a landslidePettimudi
Delve Landslide Wednesday, August 19, 2020 - 16:38

Karuppayi was fast asleep when she woke up to her neighbour screaming. It was around 10.30 pm on August 6. The neighbour’s scream forced two of Karuppayi’s male relatives to step out of their house to check what was happening. But they went back to sleep thinking the commotion may have been due to the overflowing river in the valley below. 

She, however, couldn’t go back to sleep. An hour or so later, Karuppayi heard the screams again and came out of the house. Within minutes, the back wall of her house was reduced to dirt, collapsing under the weight of a heap of soil that rained down on the village.  Filled with terror, Karuppayi ran to the road. 

The 54-year old woman is one of the few survivors of the landslide which occurred at Pettimudi in Kerala’s hill district of Idukki on August 6. The tragedy has claimed the lives of 62 people, including 19 children. Around eight people are still missing, with their bodies yet to be retrieved.  

While Karuppayi managed to escape, she lost 13 members of her family including three of her children, six grandchildren, and her younger sister. She and her siblings were living in layams (housing quarters for tea estate workers) adjacent to each other. 

Read: Koovi, the dog who waited days for owner, helps find toddler’s body in Idukki landslide

“We were living there for years, used to work in the tea estates. Everything is gone...,” 

Karuppayi tells TNM, unable to finish her sentence, breaking into tears. 

The landslide in Pettimudi comes nearly a year after a similar tragedy at Kavalappara in Wayanad district on August 8, 2019. The landslide in Kavalappara left 46 people dead, while the bodies of 13 people are yet to be recovered. 

Pettimudi was believed to be a ‘safe zone’, not prone to any disasters in the past, say residents and authorities. Was it really a safe zone? So how and why did the landslide occur? 

Tremors and hydraulic pressure 

CS Soman, a retired geologist of the Centre for Earth Science Studies, says that tremors triggered by hydraulic pressure could have caused the landslide. The hydraulic pressure was in turn caused by days of intense rainfall in the area. 

“Large, broken boulders can be found in the debris or the sort of materials that came down in the landslide. These boulders generally can be found only in fracture zones. This implies that this was a tectonically active area (tectonic zone) sometime in the geological past. The tectonically active area must have been dormant or stable for a long period, but it won’t be the same forever,” he says, adding that the trigger for the landslide in Pettimudi was incessant and extremely heavy rains.

Tectonics is the movement of the earth’s surface. It is as a result of the tectonics that continents move and earthquakes, tsunamis occur and mountains are formed.

Soman says that fractures which appeared on the tarred road surface on the south of Pettimudi and on the Munnar road is evidence of the tremors.

“Such fractures appear only during the time of tremors big or small. The whole of Munnar, in a way, are tectonically small active regions,” says Soman. However, as seismic activity below 3 on the richter scale isn’t measured, a number of these minor quakes are never recorded, he explains, “The conventional approach in India is that the richter scale is fixed at three and hence the tremors below that won’t be measured.”

Arguing that the tremors in Pettimudi would have been below 3 on the richter scale and therefore not recorded, the geologist says, “If there were no tremors there won’t be any fractures on the road.” 

The region, where the landslide took place, is a valley, explains Soman. The upper part of the valley merges with a saddle (the lower area that connects two mountain ranges). “Every saddle in a hill range is always a tectonic zone,” observes Soman, stating the sheer amount of rainfall received in the fractured area could have triggered the landslide. 

Pettimudi falls under the region of Eravikulam National Park. As per the data provided by the National Park, the rainfall on August 3, four days prior to the landslide, was 111 millimeter. The following day it was 195 millimeter, while on August 5, the region recorded 93mm of rainfall. August 6 saw intense rainfall, with 309 millimeter recorded in a single day. Thereafter, on August 7, Pettimudi and the surrounding region received 157 millimeter of rainfall.

Sajin Kumar, Associate Professor of Geology at Kerala University, also says that in the history of landslides in Kerala the major push has been heavy downpour. “The high rainfall in a short period should have played the triggering role,” Sajin says of the Pettimudi landslide. 

“Also the area where the landslide occurred was a flat-topped hill prior to the disaster. In a flat-topped hill the water collected would come down to the hill during a downpour, unlike in a three dimensional hill where the water would scatter all the way. In the case of a flat-topped hill, maximum water would be pooled in one gully,” he adds.

Age of rocks

The second factor that led to the landslides, Sajin says is the age of rocks. “We have very old rocks that are 200 crore years old. The rocks get saturated with water depending on its solid nature. If the soil is rooted in one meter, rainfall of two or three days is enough for it to get saturated. Once it's saturated, water won’t be able to permeate. And what happened in Pettimudi is that the huge volume of water collected at one point of the hill pushed the saturated soil which could be the main factor that led to the landslide.”

Sajin also says that from the curved portion of the hill where there landslide occurred in Pettimudi it could be assessed that a landslide had occurred some 50 years ago at the spot, prior to the planting of tea saplings in the region.

Several regions of the state are landslide prone areas, he says, citing the 4726 landslides that occurred in 2018 of which 800 were in the forest regions. Of the 4726 landslides, over 2500 occurred solely in Idukki.

Need for large-scale mapping and real-time data

Countering the claims of residents and authorities, Sajin Kumar says that Pettimudi must be a vulnerable area only. However, given the scale of maps, places like Pettimudi, a village in Idukki, may not be clearly mapped as a vulnerable area.  

“The question is how much real earth is represented in a map. We need maps that will cover all the red zones in it," he argues.

Soman says that large, flood zonation maps need to be prepared. “Large maps should be prepared featuring many things that hitherto have not been factored, flood zonation maps also need to be prepared, and three erosion zones in coastal areas should be demarcated. These maps are needed to prepare hilly terrains, inlands, and coastal regions for any future calamities,” he says.

Sajin suggests the need for an early warning system to minimize the effects of natural disaster.

“If there is one meter thickness of soil on a rock, 100 millimeter of rainfall in three days is a trigger for a landslide. This is called early warning. For this we need a network of rain gauges which can provide data in a real-time manner. In Kerala the rain gauges, mostly those under the government agencies, collect the rainfall data a day after the rainfall occurred. What we lack is real-time data and the best thing can do is to provide an early warning to minimize the effects of natural disasters,” he suggests.

‘Human responsibility high’

Usha Soolapani, an environmentalist points out that the Western Ghats has become more vulnerable despite claims to the contrary. “It has been two-three years that the state has been witnessing severe drought and heavy rains. No study has happened about the nature of the soil. In Puthumala and Kavalappara where the landslide occurred last year, there were quarries functioning nearby. We keep saying that the Western Ghats is stable despite the vulnerability having increased,” Usha Soolapani says, adding, “We are ignoring that climate change has affected the earth, making it more vulnerable. It’s not about hilly districts like Idukki or Wayanad, but the whole state is vulnerable. In Pettimudi, our presumption was that it was safe because of tea plantations. But we never went back and checked after all these years.” 

Soman says Pettimudi’s vulnerability was everywhere on the earth’s surface but was overlooked by everyone.

“No one can deny the human factor in the disaster. If there was a forest or a lot more trees, the landslide wouldn’t have extended three kilometers down from where it originated. And from the government side, if it was demarcated as a dormant area, human settlement should have been discouraged, considering the geological peculiarities,” says Soman. He observes that fracture zones were present throughout the estate, down in the valley where the layams were situated too. He moreover points out that when the layams were built, it would not have been listed as a tectonic or fracture zone. “But it has been decades and there was enough time for studies and action. Human responsibility is too high,” he says.  

Also Read: In devastating landslide in Kerala’s Pettimudi, 18 members of a family die

‘Bodies appeared like they were still asleep’: Eyewitnesses recount Kerala landslide

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