KOCHI: With the intense burst of rain from August 14 to 18 causing changes in slope stability, leading to hydrogeological instability in certain areas of Idukki district, the Department of Geology has recommended a study by the Geological Survey of India into the complex nature of these events.
The recommendation has been made to ensure the area is safe for construction of houses.
With Idukki witnessing a series of landslides and debris flow, the residents who have shifted to relief camps are refusing to return to their houses.
According to Idukki geologist B Ajayakumar, as many as 42 incidents of earthflow have been reported in the district. As a result of continuous rainfall, land became saturated with water and cracks appeared in many parts of the district. The cracks then widened and the earth moved downslope under the pull of gravity. The vertical displacement was around two metres deep. The situation did not worsen as the rain subsided. But a detailed study is needed to ensure the safety of houses in the area, he said.
A team of officers from the Geology Department inspected places like Vazhavara, Mavady and Murikkassery where earthflow was reported.“While the normal rainfall is 1,835 mm, Idukki received a rainfall 0f 3,555 mm from June 1 to August 22. The extremely heavy rainfall has triggered hydrogeological activities like landslide, debris flow and earthflow. The earth on the subsurface here has more clay content. The clay will absorb the water, but it has low permeability. It has low hydraulic conductivity, which means the water cannot move through pore spaces or fractures. This leads to landslides and earthflow,” said Ajayakumar.
At Mavady in Idukki, the ground floor of a two-storey house sunk into the earth, which geologists explain as a geological activity called subsidence. It is the sudden sinking of the earth’s surface due to the movement of subsurface earth material.
“The particles of clay are too fine and the ground water will erode it. The subsurface cavity will enlarge in due course of time and gets interconnected. This will lead to formation of conduits and groundwater will flow through it. This phenomenon, called soil piping, will lead to subsidence,” said Kerala University Geology Department assistant professor K S Sajin Kumar.
US experts to visit Idukki
A team of experts from the Geotechnical Extreme Events Reconnaissance Association sponsored by the US National Science Foundation will visit Idukki to study the earthflow and landslides in the district. The team led by Michigan Technological University associate professor Thomas Oommen will have University of Arkansas associate professor Richard Coffman in it. The American team will tour Idukki district from September 2 to 10.