The fieldwork in the Bhutan Himalayas, funded by Swiss Polar Institute, was successfully executed in association with the National Centre for Hydrology and Meteorology of Bhutan (NCHM), Cryosphere Service Division (CSD), Ministry of Economic Affairs and Royal government of Bhutan. The team was comprised of 15 individuals: 5 NCHM officials and 10 personnel. The duration of the fieldwork was from 16 September to 17 October 2018. This period marks autumn in Bhutan. We experienced no or only little rain and storms in the field. This small window of time is very precious and is the best period to carry out fieldwork in Bhutan and glacio-hydrological work on the Thanagang glacier. We had to cross forests, rivers, bare mountains and valleys, muddy paths and cliffs in order to arrive at our field sites. The weather during our entire trip was mostly sunny and warm with temperatures ranging between -4 and 10C.

Since the group was quite large and the elevation gain per day was significant, for instance between 400 and 700 m, we had to take enough time to acclimatize ourselves and avoid altitude sickness. We made an acclimatisation hike to Maloongang before crossing Thole La pass (4800 m). Concretely, it took us seven days on foot to arrive at our glacier and glacial lake sites. Our nightstand was mostly inside a portable tent. We also encountered a few temporary guesthouses, made up of wood, on the way. We also met nomads and their yaks and sheeps. As a mean of transport of field equipment for the survey, we did not rely much on aeroplanes and choppers, as one might expect. Due to the remoteness of the field sites, our food and equipment was carried by 25 healthy horses.

Our survey started with the bathymetry measurement at Chubda lake, located in the eastern ridge of the Bhutan Himalayas, facing south at 4800 m. Since the lake is huge (~1.5 km2) and the measurements were only possible before noon, it took us four days to complete the survey. Half of the survey days were affected by wind and water currents making it harder for rowing the boat. A sonar mounted on the boat carried out the survey. The position of the lake shoreline was surveyed by both non- and differential GPS. The lateral and terminal moraines were surveyed using range finder equipment. We also investigated Thanagang glacier, a benchmark glacier for mass balance measurements of glaciers in the Bhutan Himalayas according to the NCHM officials, as they have been monitoring these glaciers since 2012. There, we replaced and installed glacier stakes at the accumulation and ablation regions. In addition, we also carried out a GPS survey, an ice radar survey and measured density of snow by digging a snow pit. The highest accessible elevation in the accumulation region is ~5600 m.

© Sonam Wangchuck

In the field, the majority of us suffered from mild illness such as headache, sore throat, cough, and body pain. I have personally learnt to appreciate the value of this glaciological data collected in the Bhutan Himalayas. I personally felt that the collection of data in Bhutan Himalayas is like a trade between life and science. Many fatal risks are being involved in data collection such as Acute Mountain Sickness, skidding into a lake, getting hit by a rock fall, sliding into rubbles or falling into a crevasse. A sudden earthquake could easily take our lives as boulders are simply hanging on a cliff and they are highly unstable. According to the NCHM officials, there are cases of live losses, while going for a data collection, mainly because of altitude sickness. We were very grateful that none of our team members suffered from altitude sickness nor had a fatal accidents. Through the experience of NCHM colleagues and with a supplement of synthetic medicines and local herbs, we were able to overcome this mild illness, and everybody returned home safely. My special thanks goes to the colleagues of CSD for making this field trip a great success and enjoyable.

Sonam Wangchuk is a PhD student at University of Zurich. This field note relates to his expedition to Bhutan Himalayas in September and October 2018 funded by a Polar Access Fund grant.

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