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6 Jun 2016 | News

Understanding the Mass Balance of Yala Glacier

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At an elevation of 5250 metres above sea level, a bamboo stake, about an arm’s length, stuck out oddly against the white backdrop of Yala glacier. It was one of the nine bamboo stakes installed by researchers from the International Centre for Integrated Mountain Development (ICIMOD) to monitor the ice loss and gain of Yala glacier, also called the glacier mass balance.

Dorothea Stumm, Senior Glaciologist with ICIMOD, carefully measured the length of the part that was sticking out and wrote down the readings without disturbing the surface snow around the stake. By noting the readings, she could compare the readings with records from her last visit in November 2015.

‘Measuring stakes only does not give the whole picture, we have to dig snow pits to measure the height and weight of the snow on top of the glacier ice. Last year, the glacier surface was a few centimeters lower than the previous year, indicating that there was a mass loss’, Stumm said.

The glacier mass balance is like a household budget that has income and expense. Equivalent to the income, accumulation includes any processes that add mass to the glacier. Similarly, the expenses correspond to the ablation, which includes all processes that make the glacier loose mass. The main process of mass gain is accumulation from snow, and the main process for melt is the temperature. This measurements give important information on these climate variables. At the end of the mass balance year, the accumulation and ablation are added to calculate the mass budget, similarly the like we add up the income and expenses in the household budget. Depending on the readings of the stake measurements, researchers can determine whether it has been a good year for the glacier or not.

Sharad Joshi, Associate Glaciologist at ICIMOD set up the base station for differential GPS (dGPS) survey.

In the past four years, researchers with ICIMOD have measured a negative mass budget, which means that the glacier shrank. The mass balance measurements provide an excellent accurate climate indicator for the measurement period and is highly valued once a long-term measurement series is available.

Dorothea Stumm and her team of researchers from ICIMOD trek up to the mountains of Langtang valley twice every year to study the impact of climate change on Yala Glacier and conduct mass balance measurements.  Yala glacier is also used for conducting training on field based cryosphere activities.

Stakes installed on the glacier help understand how much ice melted and snow accumulated within one season or a year. Each stake represents an area of similar slope, aspect, elevation of glacier. The stake network should represent the entire glacier. Each of these stakes measures up to six metres in length when first installed with major part going into the glacier ice. A newly installed stake emerges up to two metres from the glacier, depending on how much ice melt or snow accumulation is expected for the coming measurement period.

‘Given the warmer temperatures on lower elevations, the mass gain in winter is typically less on the glacier terminus than in the upper area of the glacier. In the last four years, the glacier lost more mass in summer, than there was mass gain in winter’, said Stumm.

Further up on the glacier, Sharad Joshi, Associate Glaciologist and his team were conducting differential GPS surveys (dGPS). The dGPS surveys included surface measurements of the glacier profile line and several transects, stake location, glacier outline and shoreline of the lake.

Tika Gurung, Research Associate Glaciologist spreads saw dust on the glacier surface to mark accumulation for the next measurement.

“The main advantage of this kind of survey is we can cover larger area than with the stake method” said Joshi.

The dGPS surveys of the glacier are used to monitor changes in glacier surface.  It is another independent method to look at the mass balance through surface change measurement annually. The measurements on Yala Glacier are done every two years only.

Each dGPS measurement records the location’s coordinate (latitude, longitude) and elevation. Compared to normal GPS, dGPS gives greater accuracy. For the glacier surface measurements, the dGPS team walked many zigzag lines to assure good coverage for later comparison, walking about 20 km.

The study of glaciers is essential for the region as glaciers influence the hydrological cycle and water availability. Glacier mass balance data is globally relevant as a climate indicator. Through these measurements, ICIMOD and its partners have contributed to global glacier mass balance datasets collected by the World Glacier Monitoring Service (WGMS).

The Cryosphere Initiative of ICIMOD is funded by Royal Norwegian Government and focuses on monitoring of glaciers, snow, and glacial lakes and glacial hydrology with an emphasis on in-situ measurements, remote sensing, and modelling. Capacity building of its partner institutions is also an integral part of the initiative.

Activities are carried out in collaboration with corresponding agencies in its regional member countries.  In Nepal, its main implementing partners are Department of Hydrology and Meteorology (DHM), Kathmandu University (KU) and Tribhuvan University (TU).

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