Glaciology at IMSc
R. Shankar, The Institute of Mathematical Sciences, Chennai

Glaciology is a part of the earth science, the field of science that tries to understand the complex processes that govern the strucure of the earth. This includes its atmosphere, and how it changes in time. As you can appreciate, earth science is basic to understanding our environment and its changes.
Glaciology concentrates on the cryosphere, namely all the ice on earth. This is mainly in the polar regions. There are huge ice sheets in Antartica and Greenland and a large amount of floating ice around the north pole. The next region, in terms of the volume of natural ice, is the Himalaya, consequently, often called the "Third Pole". 'Himalaya' is made up of the words 'Hi, meaning 'ice', and 'Alaya', meaning 'home' or 'abode'. Our research, in collaboration with scientists in the HNB Garhwal University, Srinagar (Uttarakhand) and IISER, Pune, is on the "Him" of the Himalaya.

Ice in the Himalaya
The ice in the Himalaya is mainly in the form of rivers of ice, called valley glaciers. These are very high, at elevations more than around 3500 meters above mean sea level. At these elevations, much of the precipitation is in the form of snowfall. In the higher altitudes, say >4500 m, this snow does not melt since the temperature is below 0C for most of the year. It compresses to form ice which slowly flows down the valley at speeds of around 10-50 m/year. When it reaches the lower altitudes, it melts to form a stream. Many such streams combine to form rivers like the Ganga.

The making of the Ganga
We have been studying the Satopanth Glacier in the Uttarakhand. The coordinates of our base camp for field studies are (30.779749N 79.408427E). If you type these numbers into the programm called Google Earth online, you will be able to view the region of our research. You can see the Upper Ganga region with its glaciers and the rivers Bhagirathi, Mandakini, Alaknanda and Ganga in the figure.

Why study Himalyan glaciers?
My motivation is simply that it is a natural phenomenon. All natural phenomena are worth studying and understanding in detail, especially when it relates to our environment. This is a long term point of view. However, from a more practical, shorter term point of view, the interest is in how the present, rapid changes in climate will affect the river flow in the upper regions of the Gangetic and the Indus basins.

How are glaciers studied?
As in all science, it is a combination of observations and mathematical modelling. Observations tell us about the present and past state of the glaciers. The large scale observations come from remote-sensing data, namely satellite images. When you actually go to the site and take data for analysis, it is called 'Field studies'. Through field studies at individual glaciers, we can check that the remote sensing data is correct. This is called validation.
This data is then used as an input into mathematical models. These models are based on physical principles and help us understand the complex processes. Once the processes are reasonably well understood, they can be used to predict what will happen in the future.

What have we been doing?
We have been doing detailed field studies on the Satopanth and Bhagirath Kharak glaciers. These are the glaciers whose streams form the Alaknanda river, a major tributary of the Ganga. They are situated around 14 km upstream of Badrinath, Uttarakhand. Before the Covid happened, we were trekking up to the glacier twice a year and measuring quantities such as
. the speed at which the ice was flowing at different points of the glacier,
. the rate at which the ice was melting, the weather conditions,
. the amount of water that flowing in the stream coming from the glacier,
and several other things.
We have also been studying satellite images of all the glaciers in the "Upper Alaknanda Basin", namely all the glaciers that contribute water to the Alaknanda river at an elevation of around 2300 m. Finally, we have been analysing all the data we gathered from these observations and have been trying to understand them using mathematical models. As professional scientists do, we have been publishing our results in scientific journals.
Satopanth and Bhagirath Kharak are examples of extensively debris covered glaciers (DCG) (see Box). A large fraction of the lower area of such glaciers are covered by a layer of debris consisting of boulers of different sizes and sediments. This affects the melt rates in the lower altitudes and hence how they respond to changes in the climate. A significant fraction of the Himalyan glaciers (approx 20%) are DCG. Our research has concentrated on aspects of how the DCG in Himalaya respond to changes in the climate.

BOX: Debris covered glaciers
The word 'debris' means loose, natural material consisting especially of broken pieces of rock or boulders. Whenever we think of glaciers, we think of a shining white river of ice and snow. These are the so-called 'clean ice' glaciers. Himalayan glaciers are not so pretty. They look like 'rivers' of broken rock, with the water missing! This is because the ice and snow below is covered by these broken rocks, or debris. Just like clean ice glaciers, these debris covered glaciers also flow, although very slowly. A large part of the lower area of such glaciers is covered by the debris compared to the upper part, which are mostly at higher altitudes. The photograph of Satopanth shows that the lower regions are grey due to the thick debris cover. The higher elevations are white showing that there is no debris there.
END OF BOX 
What new insights have we given from our research? The following are two results, which in my opinion, are quite significant.

DCG and Climate change
In one paper, we pointed out that DCG respond to changes in the climate very differently from those without debris, called debris-free glaciers (DFG). In a warming climate, both lose volume. However, DFG do so mainly by shortening; their length decreases rapidly but their thickness decreases more slowly. On the other hand, DCG do so mainly by thinning, their thickness decreases rapidly but their length decreases more slowly. This insight helped us resolve the puzzle of the observation of a large number of "stagnant glaciers" in the satellite data. Namely a significant fraction of the DCG were not showing any change in length despite a warming climate. We realised that these glaciers were losing ice volume by thinning.

Snow on DCG
In another paper we pointed out that the input of snow/ice into DCG is dominantly (around 90\%) in the form of avalanches as compared to snowfall. Even before we published our results, the experts in the field were aware that avalanches probably contribute significantly to the accumulation of ice in DCG. This is because avalanches not only deposit snow and ice on the glacier but also a lot of debris. We calculated the fraction of snow that had accummulated due to avalanches and showed that it was very high.
While taking these measurements, we learned a lot, enjoyed a lot, and made friends with the locals who live in the nearby villages. I am looking forward to going back there again, come Summer, when hopefully, Covid is gone.