Breach, avalanche? Cause of flood divides scientists
NEW DELHI: There was no consensus till Monday evening on what exactly may have triggered the flash flood in the Rishiganga valley on Sunday. At least 26 people have died and 171 were still missing till the time of going to print. US-based scientists who looked at satellite images suggested it was caused by a landslide onto a glacier which led to debris flooding the river, while Dan Shugar of the University of Calgary suggested a landslide triggered an ice avalanche.
Not everyone agrees. Jimmy Kansal, deputy director, The Snow and Avalanche Study Establishment of the Defence Research and Development Organisation, said: “There was no landslide or avalanche. There could be a glacial lake which led to the breach, but we are still investigating that.”
The glacial lake theory (which means the flooding was a glacial lake outburst flood, or Glof) is supported by scientists at the Divecha Centre for Climate Change at IISc, Bengaluru, who say they have found clues to the origin of the flash floods. The team has concluded that release of water from an underground glacial lake led to flash floods and inundation in the valley.
Glacial lakes are typically formed when a glacier retreats, with water collecting in the area
where the glacier used to be, and dammed by the moraine. There are also instances of glacial lakes being damned by ice. When the dam bursts, it causes a Glof, resulting in flooding downstream, which is exactly what happened in this case.
The team at Divecha Centre used a tool to map the depression in bedrock below the Nanda Devi glacier and said the data suggests a depression of 25 ha upstream of glacier terminus.
The lower part of the ablation zone (zone of the glacier which has melted or calved and formed a lake), the scientists added, receives a significant amount of water from a tributary glacier at the northern side of the Nanda Devi glacier. “If this depression filled with water develops appropriate
hydrostatic pressure, it can accelerate the lower part of the ablation zone, possibly releasing water from the underground lake. It could be the potential reason for the flood,” a note prepared by IISc team said.
“This is a new tool developed in IISc which can be very useful to study such disasters. It is based on Laminar flow equation and surface slope; known as Himalayan Glacier Thickness Mapper. The tool was used to map depressions below South Lhonak lake in Sikkim and further estimate future expansion of the lake,” said Professor Anil Kulkarni, distinguished scientist, Divecha Center.
Responding to the US-based scientists who said the floods may have been triggered by a landslide, Kulkarni said, “It appears to me they looked at the adjacent valley. Initial reports suggest flash flood was caused due to breaking of Nanda Devi glacier...We went deeper to see what happened under surface.”
But the landslide theory has other subscribers.
Uttarakhand chief minister Trivendra Singh Rawat said scientists of Indian Space Research Organisation have revealed that the tragedy was caused by a mix of snow and rock avalanche and that satellite images have shown no glacier breakage.
A glacial break usually means a piece of the glacier breaking off as a large piece of ice. That does not seem to have happened in this case.
Rawat said ISRO scientists told him that a few days back there was snowfall in the affected area. “And from one trigger point due to rockfall at the top, it all slid downwards. Due to all this, lakhs of tonnes of snow came gushing down which led to the tragedy. The ISRO scientists said the satellite imagery doesn’t show any glacier breakage and that this area is not avalanche-prone.”
Pradeep Srivastava, scientist at Wadia Institute of Himalayan Geology Dehradun said that data suggests the tragedy was not caused by any glacial outburst. “Due to freezing and thawing, a rock mass broke away and slid down...This created a melting layer near debris. An avalanche was evident from the huge clouds of dust...,” he said.
MUMBAI: The Reserve Bank of India (RBI) on Monday announced that it will purchase government securities worth ₹20,000 crore through open market operations (OMOs) in a bid to cap yields of treasury bonds and support an expanded government borrowing programme.
“The Reserve Bank stands committed to ensuring the availability of ample liquidity in the system in order to foster congenial financial conditions,” an RBI notification said on Monday. “On a review of current liquidity and financial conditions, therefore, the Reserve Bank has decided to conduct purchase of government securities under open market operations (OMO) for an aggregate amount of ₹20,000 crore on February 10, 2021.”
The central bank will purchase long-term security maturing in 2024, 2028, 2030 and 2034, the notification said.
The bond market had been waiting for the OMO announcement ever since the government announced in the budget its intent to raise ₹12 lakh crore for the next financial year and an additional ₹80,000 crore for this year. RBI in its monetary policy on Friday, however, did not give any explicit guidance on the same, which disappointed the market. The yield on the 10-year bond on Friday had jumped to 6.17%, the highest in more than five months. However, it cooled off after the OMO announcement with the benchmark 10-year yield closing 3bps lower at 6.04%.
Also on Monday, Bloomberg reported that RBI is expected to buy more than ₹3 lakh crore ($41 billion) of sovereign bonds in the next fiscal year to support the government’s borrowing plans, citing a person with knowledge of the matter. This will exceed the ₹3 lakh crore the RBI is expected to spend for the current year ending March, the
report added.