Killer Slope Failures

text & pictures by TSERING TASHI

Because of geological fragility, high relief, frequent earthquakes, Indian summer monsoon and drainage basin characteristics, Sikkim and Darjeeling in particular, and rest of the Indian Himalayas in general, will be eternally plagued by natural hazards such as earthquakes, mass wasting processes (destructive or benign), differential settlements and/or subsidence, floods etc.
Therefore, all stakeholders must undertake serious scientific studies to generate relevant database for better understanding of the processes that govern the Himalayan geo-environment; share pertinent data to understand how upland environmental degradation exacerbates floods, climate change etc. in the plains; know river basins at different geomorphological levels  in different geoenvironmental settings, using similar methods and approaches to monitor changes and identify critical parameters; prepare hazard maps showing disaster prone and affected areas to help increase public awareness and avoid settlement in disaster prone locations; monitor & audit all weak rock formations and soil/ debris slope forming materials to minimize danger to life, properties & other infrastructures and so on.
Manmade rock bursts or rock falls (left photo) and natural earthquake-induced debris flow (photo on right above) are not uncommon on vehicular roads and other locations of Sikkim especially during southwest monsoon. Such slope failures are generally sudden, dangerous and damaging.
On 23 June 2014, three young teachers of Tanek Government School, North Sikkim, were tragically crushed to death in their own car by a sudden rock burst/ fall while proceeding to work. At Rolep village, near Rongli, East Sikkim, seven people, including four of a single family, were killed by a similar high speed event which is called debris avalanche on 07 June 2012.
In Sikkim, catastrophic slope failures have killed more people than any major earthquake between 1934 Indo-Nepal (Mw= 8.3) or 1950 Assam (Mw=8.7) and 18th September 2011 of Sikkim-Nepal (Mw=6.8). The largest death recorded in a single event was that of Manul, North Sikkim, on 11 September 1983, where a massive debris avalanche wiped out almost the entire GREF Camp killing 65 of its personnel.