The floods that hit two hydroelectric plants and damaged villages in northern India were triggered by a rupture in a Himalayan glacier upstream. See how glaciers and glacial lakes form and why they can sometimes break:
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HOW GLACIERS AND GLACY LAKES FORM
Glaciers are found on all continents except Australia and some are hundreds of thousands of years old. A large cluster of glaciers is in the Himalayas, which is part of the long northern border of India. Sunday’s disaster occurred in the western part of the Himalayas.
Glaciers are made up of layers of compressed snow that move or “flow” due to the gravity and softness of the ice in relation to the rock. The “tongue” of a glacier can extend hundreds of kilometers (miles) from its origins at high altitude, and the end, or “snout”, can move forward or backward based on the accumulation or melting of snow.
“Ice can flow through mountain valleys, spread across the plains or, in some places, spread across the sea,” according to the National Snow and Ice Data Center.
Proglacial lakes, formed after the retreat of glaciers, are often limited by sediments and rock formations. Additional water or pressure, or structural weakness, can cause the rupture of natural and artificial dams, sending a mass of floodwater through rivers and streams fed by the glacier.
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WHY DO I HAVE THIS GLACIER?
It is not yet known what caused part of the Nanda Devi glacier to break off on Sunday morning, sending the floodwater downstream towards power plants and villages in the northern Indian state of Uttarakhand.
Seismic activity and increased water pressure can cause glaciers to burst, but one particular concern is climate change. High temperatures combined with less snow can accelerate melting, which causes the water to rise to potentially dangerous levels.
“Most mountain glaciers around the world were much larger in the past and are melting and decreasing dramatically due to climate change and global warming,” said Sarah Das, an associate scientist at the Woods Hole Oceanographic Institute.
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CAN SUCH DISASTERS BE FORECASTED?
Deadly or highly destructive glacial floods in the past have occurred in Peru and Nepal.
But remote glacier locations and a lack of monitoring mean we don’t have a clear understanding of how often they occur and are increasing, said Das.
“Given the general pattern of heating, retreating glaciers and increasing infrastructure projects, however, it seems natural that these events will occur more frequently and become more destructive if measures are not taken to mitigate these risks,” said Das . .
A series of imminent and potentially deadly glacier explosion and flood situations have been identified worldwide, including in the Himalayas and the South American Andes.
But while monitoring is possible, the distance from most glaciers presents challenges.
“There are many glaciers and glacial dammed lakes in the Himalayas, but most are not monitored,” said Das. “Many of these lakes are upstream from steep river valleys and have the potential to cause extreme flooding when they burst. Where these floods hit inhabited regions and sensitive infrastructure, things will be catastrophic. “
A 2010 information page published by the International Center for Integrated Mountain Development, called for more monitoring of glaciers in the Himalayan Hindu Kush to better understand “the real degree of glacial lake instability”.
The region where the glacial overflow occurred is prone to landslides and flash floods, and environmentalists have warned against construction in the region.
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