KASARGOD: Over the past few days, a newly constructed house belonging to Sadan K, 45, of Ottamavungal near Kuttikol in Kasaragod district, has become a local hotspot. A massive cave appeared beneath his house and people are curious to have a look. The sinking is the result of a phenomenon called soil piping, or tunnel erosion, in which the soil below the laterite surface gets eroded because of water percolation.
For over three years, Sadan, a tiles worker, had been building the house, mostly by himself. He and wife Ramya, a homemaker, and their two children were planning to move to the new house on August 28. Two weeks ago, Sadan brought an earthmover to dig a sceptic tank pit. Shortly after digging, the soil caved in. So, he asked the earthmover operator to close the pit.
When he returned the next day, the soil dumped to close to the pit had vanished. Exploring the area below, Sadan came across a massive cave — a void the size of a large hall right underneath the house. A gushing stream flows inside the void, emptying into a sinkhole only to appear in a pond some 50 metres downhill in an areca farm. The void is more than 35 to 40 feet long and 10 to 15 feet wide, while the height is between 8 to 10 feet.
“The place has become an attraction but it has shattered the family’s dream of owning a house,” said his neighbour, Koran.
A few steps into the void, it becomes scary as the surface is extremely slippery due to the clayey nature and the air turns thick, causing a claustrophobic feeling. “I borrowed from banks and friends and pledged my wife’s jewels. I toiled during the night hours after my daily work to build this house. A few weeks before moving in, we are caught in this situation,” Sadan lamented, having spent `30 lakh on the house.
After he alerted the local panchayat and the district geology office, a team of geologists from Thiruvananthapuram are set to inspect the site on September 10, he said.
Confirming soil piping at play, Sooraj S, a geologist with the district mining and geology office, said: “We need to study the situation before recommending any remedial measures.”
The national and state disaster management authorities had carried out two studies on soil piping and subsidence in Kerala, in 2016 and 2020, respectively. Scientists from the National Centre for Earth Science Studies, Thiruvananthapuram, as part of those studies, found that the land subsidence (sinking of land) in the Western Ghats was due to soil piping.
The phenomenon is observed across Kerala, except Kollam and Alappuzha districts. Kasaragod, Kannur and Malappuram are the most affected by tunnel erosion while it is widespread in Wayanad, Idukki, Kozhikode and Thrissur. The studies identified 139 regions affected by soil piping in the Western Ghats.
What is soil piping?
Soil piping results in the formation of subsurface voids / cavities / tunnels due to subsurface soil erosion
During rain, percolating water carries finer silt and clay particles and forms passageways called pipes, starting from a few millimetres to grow to a metre and more in diameter with time
These pipes may lie very close to the ground surface or extend several metres below the ground
Once initiated, they become cumulative with time, the conduits expand due to subsurface erosion leading to roof collapse or sinking of land
Over the course of time, the land turns unsuitable for cultivation or construction