Scientists say massive ice structures behind Dharali disaster - What are hanging glaciers?

Dharali disaster

A 'hanging glacier' feeding the Kheer Ganga channel could have played a role in the devastating flash floods that struck Dharali on August 5, a team from the Indian Institute of Science (IISc) suspects, according to a report by Hindustan Times.

A preliminary analysis by the National Disaster Management Authority (NDMA) had already pointed towards a glacier collapse as a possible cause. Researchers at the Divecha Centre for Climate Change, IISc, have recently completed geo-spatial mapping of 219 hanging glaciers in the Alaknanda and Bhagirathi basins, as part of an ongoing study.

What is a hanging glacier?

A hanging glacier is one that begins high on a glacier valley wall and comes down only part of the way, without reaching the main glacier’s surface. These glaciers are known to be unstable and sensitive to climate changes.

Anil Kulkarni, a visiting scientist at the Divecha Centre, explained that the Kheer Ganga channel has two such glaciers nearby, together holding around 1 cubic km of ice. Historical satellite images show that the glacier’s position made it extremely vulnerable.

“There are two hanging glaciers in the vicinity with a combined volume of approximately 1 cubic km. We have historical satellite images of the glaciers. The run-off time during the flash floods was very short. Normally, if flash flood is from rainfall then we can observe a gradual increase and then a decrease. But the sudden run-off points to two probabilities. One that the hanging glacier has fallen, or a lake has formed due to the obstruction of river flow. Then sudden outburst was caused due to overflown,” Kulkarni was quoted by HT as saying.

He added that IISc has been modelling which sections of these glaciers are most likely to detach, noting that hanging glaciers start melting earlier than other types because of their exposure to warmer conditions.

Warnings ignored

Even before the August 5 floods, environmental groups had been warning about the risks in the area. As per HT, the Himalayi Nagarik Drishti Manch wrote to the Bhagirathi Eco-Sensitive Zone (BESZ) Monitoring Committee, the Ministry of Environment, Forests and Climate Change, and the Jal Shakti Ministry on Monday, calling for accountability. They referred to an earlier letter, sent on April 30, 2024, which warned of possible disasters if unchecked construction on riverbanks and hill slopes continued.

The letter had urged authorities to halt such activities immediately, stressing that these fragile Himalayan zones are highly vulnerable to climate-related events and human-induced pressures.

Massive rescue operations underway

In the aftermath of the floods, rescue teams have been working round-the-clock to locate missing persons buried under debris. The Indian Army has flown in ground-penetrating radar (GPR) devices from the Siachen Glacier to Uttarkashi. These radars are usually used in avalanche rescues and can detect buried objects and signs of life under thick layers of debris.

Officials said these additional GPRs will supplement the ones already in use by Army and National Disaster Response Force (NDRF) teams. Nearly 200 NDRF personnel are also using their own radar and life-detection devices. The State Disaster Management Authority (SDMA) has divided the 4 km stretch between Dharali and Harshil into different zones, assigning them to various agencies for targeted search operations.

Over the weekend, NDRF’s Delhi headquarters sent two more GPR devices to the disaster site. A senior NDRF officer described the conditions as extremely challenging. “There are huge mounds of mud and debris. Some multi-storey buildings are completely buried. In many areas, we have to dig manually at spots identified by locals and eyewitnesses. We are trying to make progress, but it’s slow and painstaking work,” HT quoted the official as saying.