National Highway-10, the only all-weather road connecting Sikkim and Kalimpong with the rest of the country, is fast turning into one of the most vulnerable mountain highways in the eastern Himalayas, with repeated monsoon-triggered landslides threatening to wash away critical stretches and disrupt connectivity.
A recent scientific study has warned that unless an alternative road corridor is identified and geologically sound engineering practices are adopted, the highway will continue to face frequent collapses, jeopardising transport, tourism, defence logistics and the regional economy.
The study, conducted by geographer Biswajit Bera, identifies several chronically unstable locations along NH-10—including Sevoke Kali Temple, Birik, Sweti Jhora, Kali Jhora, Geil Khola, Ravi Khola, 29th Mile, 20th Mile, Bhalu Khola, Maam Khola and Tarkhola, as highly susceptible to being washed away by landslides and severe erosion caused by the Teesta River during intense monsoon spells.
According to the study, the growing instability of the highway is no longer solely a consequence of natural Himalayan geology. A combination of factors including massive silt deposition on the Teesta riverbed following the South Lhonak Glacial Lake Outburst Flood (GLOF), the cumulative impact of multiple hydropower dams on the Teesta, expansion of NH-10, construction of the Sevoke-Rangpo railway tunnel through geologically fragile slopes, and the increasing frequency of short-duration, high-intensity rainfall events—has significantly increased both the frequency and magnitude of landslides in recent years.
“The recurring destruction along NH-10 is a warning that conventional road construction practices are inadequate for the young and tectonically active Himalayas,” Bera observed.
He stressed that future infrastructure projects in the region must be preceded by comprehensive geohazard and geotechnical investigations rather than relying solely on conventional engineering designs.
The study recommends the use of advanced Remote Sensing and Geographic Information System (GIS) technologies, including multi-spectral satellite imagery and Interferometric Synthetic Aperture Radar (InSAR), to detect historical slope failures, monitor ground deformation and identify micro-fractures before they evolve into catastrophic landslides.
It also advocates detailed engineering geological mapping to identify faults, folds and lithological boundaries so that highways can be aligned through comparatively stable terrain.
Geophysical investigations, including seismic refraction and electrical resistivity surveys, should be undertaken to map subsurface conditions, groundwater movement and buried rock structures without extensive excavation.
Bera further recommends systematic rock mass characterisation using internationally accepted classification systems such as Rock Mass Rating (RMR) and the Q-system to determine rock strength and design appropriate structural support for both highways and tunnels. These assessments are particularly important for projects employing the New Austrian Tunnelling Method (NATM).
The study also highlights the need for geo-environmental investigations involving subsurface exploration, hydrological modelling and detailed analysis of soil and rock properties, particularly in areas dominated by highly weathered phyllitic formations that are especially vulnerable to slope failures during heavy rainfall.
The findings underscore the urgent need for long-term infrastructure planning in the eastern Himalayas, warning that without scientific intervention and the development of an alternative connectivity corridor, NH-10 will remain increasingly vulnerable to recurring disasters with serious socio-economic consequences for the region.