Dammed by land­slides

Down to Earth - - SPECIAL REPORT -

Satel­lite im­ages have helped lo­cate zones in Nepal and China where land­slides can cause huge dam­age. The haz­ards these pose could be even big­ger than the Nepal earth­quake. They can block rivers, cre­ate avalanches and cause floods. In one such case, the Kali Gan­daki was dammed by a land­slide in Nepal and an ar­ti­fi­cial lake was cre­ated, forc­ing the gov­ern­ment in Bi­har (which lies down­stream) to is­sue a flash flood alert on May 23. Re­sponse teams from var­i­ous or­gan­i­sa­tions, in­clud­ing NASA, non-profit Earth­quake With­out Fron­tiers, Bri­tish Ge­o­log­i­cal Sur­vey and the In­ter­na­tional Cen­tre for In­te­grated Moun­tain De­vel­op­ment, have iden­ti­fied over 3,000 land­slides and large mass move­ments in the re­gion. Of these, a data­base of 250 sites (de­picted in the map) has been cre­ated. Four of them pose a grave threat

Pisang (Nepal): The Nepal earth­quake cre­ated a land­slide dam on the Marshyangdi river, 1.8 km up­stream of the Lower Pisang vil­lage. Satel­lite im­ages show the lake is ex­pand­ing.

Manaslu re­gion (Nepal): Tom Khola, a trib­u­tary of the Burhi Gan­dak, has been dammed by a land­slide, re­sult­ing in a lake in the Manaslu re­gion. The land­slide is at a height of 2,500 m. Though the land­slide has not harmed any vil­lage, the threat is there be­cause the new lake is up­stream of the vil­lages of Ghap­sya (5 km) and Ghap (6 km). The land­slide dam is also just 6 km from the Nepal-Ti­bet bor­der. So if the lake keeps grow­ing, it will be­come a con­cern to China.

Lang­tang val­ley (Nepal): Maps pre­pared by the Univer­sity of Ari­zona and NASA show that the Lang­tang val­ley has ex­tremely high ice avalanche sus­cep­ti­bil­ity due to the pres­ence of Hi­malayan slopes, glaciers and in­creased shak­ing dur­ing an earth­quake (which hap­pens be­cause of its el­e­va­tion). The res­i­dents of the area have ex­pe­ri­enced ice and de­bris avalanches, which is in line with the re­sults found in the sus­cep­ti­bil­ity map.

Chongse­cun (China): Cana­dian, Amer­i­can, Chi­nese, Swiss and Bri­tish in­ves­ti­ga­tors are ex­am­in­ing a land­slide in Ti­bet at an el­e­va­tion of 2,600 m. This land­slide has dammed the Gyri­ong Zangbo river and blocked a road be­tween Nepal and Ti­bet. The de­bris has been dis­placed downs­lope, form­ing a 700 m long land­slide scar.

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