GLOFs happen when ice and snow melted by the climate thaw accumulates in enlarging lakes, which can burst due to increased water pressure, or when avalanches fall into them. And while there are frequent GLOFs, especially in the eastern Himalaya, scientists agree that it was not the main trigger of the Nanda Devi disaster last month.
The other disasters on Himalayan rivers are caused by bishyari, a local word that refers to a floods due to a landslide blocking a river to impound a lake that suddenly bursts, as what happened in Jure of Sindhupalchok on 2 August 2014.
Another catastrophic example is the co-seismic mountain slide that blocked the Seti River about 500 years ago, creating a huge lake that then burst depositing the 200m thick sediment layers on which the city of Pokhara is now located.
Nepal’s former water resource minister and hydropower expert Dipak Gyawali says that bishyari are known to happen in 10-15 year cycles in Nepal. The etymology of the word itself shows that human dwellers of the Himalaya have known of the phenomenon for thousands of years, he says.
“Even if these floods are not directly caused by climate change, it can exacerbate the disaster because of extreme weather events,” Gyawali said in an interview.
Himalayan floods therefore pre-date climate change, and are caused by the vulnerability of these young, fragile mountains to natural and human-induced processes like the indiscriminate use of heavy earth-moving vehicles on poorly-engineered roads.
Such ‘bulldozer terrorism’, has exacerbated the frequency of landslides in central Nepal after the 2015 earthquake, according to a recently published paper in the journal, Progress in Disaster Science.