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Gangotri’s movements reveal its inner workings

The Gangotri glacier is the largest glacier in the Garhwal Himalaya and the source of the sacred river Ganga. Its snout movements have been tracked for more than a century, but little is known about how the rest of its 30-km length moves and changes over time. A study from the Indian Institute of Science (IISc) has now shed light on the inner workings of the Gangotri glacier by measuring its surface velocity over two decades.

The Gangotri glacier is situated in the Uttarakashi district of the Garhwal Himalayas in Uttarakhand. It is around 30 km long and 4 km wide and originates in the Chaukhamba massif, a ridge formed by four mountains. It is fed by several smaller tributary glaciers on either side. The glacier flows northwest and terminates at Gaumukh where its melt-water feeds the Bhagirathi River, one of the main tributaries of the Ganga. The glacier is a traditional pilgrimage site at which devotees flock to take a dip in its icy waters. Its sheer size and inaccessibility has made field studies of the glacier extremely difficult.

All that has changed with the advent of satellite imaging. It is now possible to track even tiny movements of glaciers from space. The author of the study, Dr. Satyabala, a visiting scientist at the Divecha Centre for Climate Change at IISc, has used sophisticated remote sensing data to measure the surface velocity across the entire Gangotri glacier over a 20-year period. The study was published recently in the prestigious journal “Remote Sensing of Environment”.

The study has found that the Gangotri glacier has seasonal variations in its flow, moving steadily in winter and speeding up over the summer as the ice melts. However there are longer-term trends as well. While the winter velocity has held steady during the entire period of study, the summer velocity showed a peak in 2004 and declined steadily from there on until 2011.

These observations shed light on the complex inner workings of the Gangotri glacier. Glaciers move by sliding along the glacier bed and through internal deformation. The sliding is strongly influenced by the melt-water that penetrates down to the glacier bed. “My results show that the intricate network of melt water channels inside the glacier is evolving across seasons and across years,” adds Dr. Satyabala.

“Although melting glaciers are iconic symbols of climate change, mountain glaciers such as the Gangotri cannot be thought of as simple blocks of ice,” adds Dr Satyabala, “Their internal dynamics are complex and poorly understood, making their response to climate change hard to predict. Satellite data allows us to take a peek inside glaciers not by going close to them, but instead by looking at them from afar.”

About the author

Dr. S P Satyabala is a Visiting Scientist at the Divecha Centre for Climate Change and the Centre for Atmospheric & Oceanic Sciences, Indian Institute of Science, Bangalore. Contact: satyabala@gmail.com

 

About the paper

Satyabala SP (2016) Spatiotemporal Variations in Surface Velocity of the Gangotri Glacier, Garhwal Himalaya, India: Study using Synthetic Aperture Radar Data, Remote Sensing of Environment, 181: 151–161. DOI: 10.1016/j.rse.2016.03.042