Glaciers

There are an estimated 54,000 glaciers in the Hindu Kush Himalayas. These glaciers cover 60,000 square kilometers and serve as a major source of the water in the region’s rivers, including as much as 40 percent in the Indus River system. On the whole, the region’s glaciers appear to be shrinking substantially.

In simplest terms, a glacier is a large body of ice that is moving from a higher to a lower elevation. It has to be at least 30 meters thick for movement to take place, and the ice is always moving from the upper part of the glacier to the lower part, or snout. That’s true whether the glacier is advancing or retreating. 

Glaciers form when precipitation falls as snow, remains in the same place year-round and accumulates enough new layers to transform into ice. Each year, new layers of snow bury the old layers, forcing the snow to re-crystallize. Slowly the grains grow larger and the air pockets between the grains get smaller, causing the snow to compact and increase in density. After about two winters, the snow turns into firn, an intermediate state between snow and glacier ice, about two-thirds as dense as water. Over time, with the continuation of the compression, air pockets become so tiny that firn becomes ice. 

In the upper part of the glacier, or accumulation zone, more snow falls than melts during the course of a year, while in the ablation zone, in the lower part, more ice and snow melts than accumulates. Lost ice is replaced by ice from the accumulation zone through transport of ice from the upper part to the lower part with the help of gravity.  But sometimes the math doesn’t work out in the glacier’s favor. The glacier mass balance, or difference between accumulation and ablation over a year, can either grow, shrink or stay the same based on environmental factors. 

Why does that happen? Changes in the amount or the timing of precipitation – for instance, whether it falls as snow or summer rain – can make a difference. So can the amount of melting due to warming. A thin layer of soot pollutants on the glacier surface may increases heating, while a thick layer of debris can act as an insulator. In most cases, the rate at which a glacier retreats or advances depends on the rate at which the total amount of ice shrinks or grows, as well as the size and geometry of the glacier. 

Most observations indicate that the Hindu Kush-Himalayan glaciers are shrinking and retreating. While there is local variation – for instance, some glaciers in the Karakorum range appear to be advancing – the trends indicate that we have only until to the middle of this century before continued deglaciation leads to a crisis in water availability.

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Datasets

In order to monitor changes in the glaciers in the Bhutan Himalaya, a repeat decadal glacier inventory was carried out from Landsat images of 1977/78(1980), 1990, 2000 and 2010. The base map of glaciers was obtained by object-based image classification method using the multispectral Landsat images of 2010. This method is used separately to delineate clean-ice and debris covered glaciers with some manual editing. Glacier polygons of 2000, 1990 and 1980 were obtained by manual editing on 2010 by separately overlaying respective years.


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Digital polygon data of Glaciers of Bhutan in 2000. This dataset is created using Landsat TM and ETM+, imageries of 2000. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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Digital polygon data of Glaciers of Bhutan in 1990. This dataset is created using Landsat MSS, imageries of 1990. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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Digital polygon data of Glaciers of Bhutan in 1980. This dataset is created using Landsat MSS imageries of 1980. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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Digital polygon data of Glaciers of Bhutan in 1980, 1990, 2000 and 2010. This dataset is created using Landsat MSS, TM and ETM+ imageries of respective years. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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Digital polygon data of Glaciers of Bhutan in 2010. This dataset is created using Landsat TM and ETM+, imageries of 2010. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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This is the inventory of glacial lakes in the Nepal Himalaya. The inventory is prepared using Landsat satellite images of 2005/2006 and gives the distribution of glacial lakes at the sub-basin level. It also contains information about three potentially dangerous lakes based on their field investigation, along with the prioritization of critical lakes.


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Digital polygon data of Glaciers of Nepal in 2000. This dataset is created using Landsat MSS, TM imageries of 2000. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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Digital polygon data of Glaciers of Nepal in 1980. This dataset is created using Landsat MSS, imageries of 1980. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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Digital polygon data of Glaciers of Nepal in 1990. This dataset is created using Landsat MSS, TM imageries of 1990. The glacier outlines was derived semi-automatically using object-based image classification (OBIC ) method separately for clean ice and debris cover and further editing and validation was done carefully by draping over the high resolution images from Google Earth.


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