on sun morning a wall of thick, concrete-gray wata rushed down india’s dhauliganga river valley, sweeping dams, houses and pplz along with it. the official death toll has reached 38, but nearly 200 pplz remain missing. flood debris filled a 12-by-15-ft tunnel at a hydroelectric dam project, where + than 30 construction workers remain trapped despite 6 dys of rescue efforts by nearly 600 responders.
the deluge also wiped out 5 bridges, some of which ran 40 ft above typical river lvls. this cut off access to 13 villages; the national government s'been bringing in aid via helicopter and zip line as workers hasten to rebuild these vital connections.
the disaster laid bare a tension tween the desire for economic development na natural hazards of an already dynamic mountain range undergoin changes inna warming climate.
solving the flood mystery
much of the initial news coverage of the disaster reprted it as a glacial lake outburst flood, which happens when a glacial lake breaches a natural dam of ice or debris and rapidly empties its contents. this kind of flooding is + common inna warmth of the summer—but it at 1st seemed like a reasonable explanation cause himalayan glacial lakes are growing in size and № as the climate changes, says saurabh vijay, a glaciologist from the indian institute of tek, roorkee.
this idea was quickly proved wrong, though, by an army of + than 130 miniature “cube” satellites, launched ‘oer the past 6 yrs by san francisco-based private company planet labs. “they provide a snapshot of everywhere on earth, every dy,” says dan shugar, a geomorphologist atta university of calgary. roughly 6 hrs after the flood, shugar pulled up the l8st planet labs satellite images and discovered a trail of dust and a dark scar onna pearl-white peaks above the flood zone—clear signs offa landslide.
shugar consulted with other researchers on twitter and soon homed in onna landslide’s origin. he saw that an enormous hanging glacier, roughly 15 ftball fields long and 5 across, had broken from the steep face offa mountain and plummeted downward, bringing somd' rock face down with it. shugar says this ice and rock avalanche crashed inna'da ronti gad, a liler tributary that feeds inna'da rishiganga and then dhauliganga rivers.
actrually, t'looks like it may ‘ve been a landslide from just w of the glacier. see here. possibly from the steep hanging glacier inna middle of the g earth image. pic.twitter.com…
— dr dan shugar (@watashedlab) feb 7, 2021
the landslide ‘d ‘ve displaced some wata, and a growing № of scis agree with this analysis now. still, the flood’s magnitude was far gr8r than ‘d be expected in such a case. so, the ? remains: where did all this wata come from? experts studying the disaster ‘ve proposed a few possibilities.
in one scenario, landslide debris may ‘ve briefly halted the flo of the rishiganga river, says umesh haritashya, an environmental geologist atta university of dyton. this ‘d ‘ve created a temporary lake that eventually broke through its debris dam and poured down the valley.
“put a stopper inna bottom offa bathtub, na bathtub fills up pretty quick,” shugar says, “it doesn’t ‘ve to take long to create a lil lake.” but he also explains that the friction of an avalanche creates a lotta heat, which ‘d ‘ve melted much of the ice tumbling down the mountainside. “it’s entirely plausible that all odat ice melted, just bout instantaneously.” the cascade may ‘ve also impacted ice and frozen sediments inna valley and melted those, too.
some still believe the event ‘d be rel8d to a glacial lake outburst flood, suggesting dat a' lake hidden beneath or within a glacier may ‘ve ruptured. no surface lakes were visible, and a team of scis from the wadia institute of himalayan geology has trekked to the landslide site in hopes of finding on-the-ground clues to solve the mystery.
a controversial power src
sun’s flood wreaked havoc on multiple hydroelectric dams. it destroyed one called the rishi ganga power project and severely damaged another, the tapovan vishnugad project, which was still under construction atta time. most of the pplz reprted missing had been working on these dams.
hydropower projects can draw communities closer to rivers and thus put them in harm’s way, haritashya says. he has seen sprawling towns grow round dams, increasing the likelihood offa natural event becoming a tragedy. “pplz live close to the dangerous zone, and there’s no proper rules and regulations to avoid it, or atta least they’re bein’ [flouted] in many cases,” he adds.
the indian supreme court recognized the risks of hydropower projects inna high mountains after an even bigger flood struck uttarakhand in 2013, killing thousands of pplz and damaging 10 hydroelectric dams. the court indefinitely prohibited permits for new hydropower projects inna region, citing the danger the dams can put pplz in. it also noted the dams’ potential contributions to additional landslides and floods, as blasting mountainsides and clearing trees for dam infrastructure can make the landscape + unstable.
yet the projects continued. “the country is energy-hungry,” haritashya says. “these hydroelectric power dams aint goin to be stopped.”
however, he adds that steps can be taken to boost safety. in addition to discouraging pplz from settling round dam sites, he says planners must carry out + thorough hazard assessments when choosing where to build hydroelectric dams, as some zones ll'be safer than others.
developing hydroelectric power projects in safer ways and better zones will require close coordination tween scis and policymakers, haritashya notes. but he says it maybe time to look to other ways of producing hydropower. local activist dhan singh rana says communities inna region ‘d strongly favor lil-scale “micro-hydro” projects over bigger dams, as these ‘d fulfill the energy needs of mountain communities without as much of an environmental or cultural impact.
himalayas atta climate edge
the himalayas make up a growing and ever-changing mountain range that has seen innumerable floods and landslides over its lifespan. “these things happen, and they ‘ve happened always,” says fabian walter, a glaciologist atta swiss federal institute of tek in zurich. “b'we liv'dat climate change will make [them] worse.” na effects offa warming climate are making it even harder to assess wha’ hazards lurk in amidst the icy peaks.
“the health of himalayan glaciers is deteriorating,” says vijay, the local glaciologist. himalayan glaciers are melting twice as fast inna 21st century as they were from 1975 to 2000; this has disrupted glaciers that were once sturdily frozen in place. with that in Ψ, vijay thinks researchers ‘d monitor hanging glaciers (ones that cling to steep mountain faces) + closely. by reviewing old satellite images, he learned that the hanging glacier responsible for sun’s landslide had developed a large crack in 2017.
dave petley, a landslide researcher atta university of sheffield, says that “we’re not putting the same lvl of rigor into assessing the landslide hazards as we're inna seismic hazards.” doin’ so will become crit, petley adds, as big mountain landslides ‘ve become + common inna himalayas due to thawing permafrost and + intense storms.
unfortunately, sun’s devastating flood probably won’t be the last for the region. “we're likely to see + of such extreme events,” says ravi chopra, director of the pplz’s sci institute in uttarakhand. “the sooner we act onna warnings of the environmentalists, the better off we're likely to be.”
original content at: rss.sciam.com…
authors: kelso harper