IT News
Imphal, July 14:
A team of five experts had submitted a survey report on what caused the massive landslide in Noney district that killed over 50 people injuring several others. The death toll has reached 54 as reported yesterday evening. A massive search operation is underway to find more bodies.
Meanwhile, a five-team conducted a preliminary survey about the cause of the landslide and submitted their findings to the Union Minister of State for External Affairs Dr. RK Ranjan on July 9, 2022.
The report is produced below:
“Geologically, non-resistant lithologies (shale inter-bedded with mudstone, siltstone, and sandstone) of Barail Group exposed in the study area after the modification of the slope geometry that impedes the mountain’s ability to resist the existing gravitational force may become one of the causes of mass wasting/landsliding.
“The process might have been initiated long back, and the entire mass wasting slump was settled along the slope of the hill. It seems that the recent precipitation during May-June 2022 became the threshold for ongoing massive landslide hazards in the study area. And due to the Ijai fault which is an 11 km long NE-SW trending fault that gets abruptly terminated against the Tupul fault north of Tupul village at the confluence of Ijai and Tupul rivers (after GSI Misc. Publication 1992, Acc. No. 2028).
“Secondly, the fluctuation in the ongoing precipitation pattern is the source of availability of more water along these slopes to percolate below the slope surface. The fine-grained lithologies (clay and silt) being less permeable becomes more plastic and reduces the stability of the slope and initiates the sliding, where the resistant lithologies (sandstone and mudstone) still hold water in their pore spaces. These two contrasting combinations of litho units in western Manipur as well as in the study area seems to be one of the causes of slope instability.
“Thirdly, Manipur state is included in the High Seismic Hazard (Zone V, Seismic Zonation Map of India) and hence, the microseismicity is active besides a large earthquake of 2016 (M6.7) which is near to the recent landslide area. Based on the fault plane solutions (Global CMT Project) of earthquake data, the principal P-axis is towards north, indicating the compression direction, resulting in the extension along the east-west. The resulting creeping of micro deformation towards the western slopes of the terrain including the recent landslide area is aligned with the principal T-axis (Kumar et al 2011). It also seems to be one of the triggering factors for the hazard as few minor cracks are observed in the cut slopes of the railway yard. Fourthly, changes in the land use patterns on the top of hills like deforestation, Jhum cultivation, and banana cultivation, also accelerated the soil erosion process and might also be the secondary factors for the recent landslides.
“ We observed that the lithological trend of the Marangching is along NW-SE which is one of the factors for ongoing deformation processes and initiating slope instability as a continuous phenomenon. We have observed during the site visit and compared with existing terrain maps as well as DEM data that the slope (42o ) of the Makhuam hill along with the first order stream drainage lines. The seasonal first-order streams along the slope of the hill are the main source of water percolating on these slopes, which become more prone to mass wasting because gravity has an easier time pulling materials down a steep slope as compared to a gentle slope. Heavy incessant rainfall and too much water also weakened its ability to resist gravity. However, a little bit of water actually made it easier for soil particles to bond together and keep the mountain intact.
Generally, soil particles lose this bond and break apart after excessive rain. The primary effect of water within the slope was to reduce shear stress (reduced cohesion) acting along the potential slip surface, thereby reducing the shear strength along the surface. The driving force (or moment) is due primarily to the component of the slump block weight acting parallel to the potential slip surface. Movement could be triggered if the ratio of driving to resisting forces (or moments) is altered by adding water by rainfall (60% above the normal rainfall in the last two months) to the slope. This seems to be the main causative factor for the recent massive landslides”.
The expert team are : – Prof. Arun Kumar – Manipur University, Dr. Manichandra Sanoujam – Manipur University, Dr. Thingujam Dolendro – Geoconsult India, Moirangthem Jagajit Singh – Computer Gallery Imphal, Dr.N. Sanamacha Singh – ECC, S.K. Gainaimei – ECC and R.K.Bikramjit – ECC.
