Recent Glacier Shrinkages in the Lunana Region, Bhutan Himalayas

13 Recent Glacier Shrinkages in the Lunana Region, Bhutan Himalayas Nozomu NAITO 1*, Ryohei SUZUKI 2, Jiro KOMORI 3, Yoshihiro MATSUDA 4, Satoru YAMAGUCHI 5, Takanobu SAWAGAKI 6, Phuntsho TSHERING 7 and Kharka Singh GHALLEY 7 1 Department of Global Environment Studies, Hiroshima Institute of Technology, 2-1-1, Miyake, Saeki-ku, Hiroshima 731-5193, Japan 2 Shin-Yokohama Office, Fujitsu Software Technologies Co.Ltd., Yokohama 222-0033, Japan 3 Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan (Present affiliation: Department of Modern Life, Teikyo Heisei University) 4 Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya 464-8601, Japan 5 Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Prevention, Nagaoka 940-0821, Japan 6 Faculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan 7 Department of Geology and Mines, Ministry of Economic Affairs, P.O.Box 173, Thimphu, Bhutan *e-mail: naito@cc.it-hiroshima.ac.jp Abstract Two debris-covered glaciers and two debris-free glaciers were surveyed regarding their surface lowering in the Lunana region, in the northern part of Bhutan. Regarding the debris-covered ones, the lowering rates were estimated to be 0-3 m a -1 and approximately 5 m a -1 on the ablation areas of the Thorthormi and Lugge Glaciers, respectively, in 2002-2004. Glacier flow was also measured for the two glaciers. The results showed contrastively that compressive flow is clear on the Thorthormi Glacier but not on the Lugge Glacier. The contrast in the surface lowering and flow is discussed herein to infer a positive feedback mechanism between glacier shrinkage and glacial lake growth. On the other hand, the surface lowering rates evaluated on debris-free glaciers were 3-4 m a -1 on the lower part of the Jichu Dramo Glacier in 2003-2010, and 1-3 m a -1 on a small unnamed glacier southeast of the Jaze La (pass) in 1999-2010. The lowering rate on the Jichu Dramo Glacier may have accelerated from the previous estimate in 1998-2003. In addition, several pairs of repeated photos are provided to show glacier shrinkages and retreats. Key words: Bhutan Himalayas, debris-covered/-free glacier, field survey, glacier variation 1. Introduction The variations of mountain glaciers and ice caps worldwide have recently attracted considerable attention due to their significance with respect to rising sea levels. Summer-accumulation type glaciers in the Asian highland regions, including the Himalayas, are considered to be particularly vulnerable to global warming (Ageta, 1983; Fujita & Ageta, 2000; Naito et al., 2001). This is because snowfall during summer can easily transform into rainfall, and the decrease in fresh snow can reduce the surface albedo of glaciers, which can lead to lesser accumulation and greater ablation of the glaciers. In reality, relatively rapid glacier shrinkages have been reported in the Nepal Himalayas (e.g., Fujita et al., 1997; Naito et al., 2002). On the other hand, Bhutan, which is located near the eastern edge of the Himalayan range, receives heavier precipitation than Nepal (Eguchi, 1994) Global Environmental Research 16/2012: 13-22 printed in Japan due to a stronger influence of the Asian summer monsoon. Karma et al. (2003) reported that the recent retreat rates of glacier termini in Bhutan are almost twice as large as those of glacier termini in eastern Nepal obtained by Asahi (1999); further, they suggested that these differences may have resulted from the stronger influence of the summer monsoon in Bhutan. In order to evaluate the volumetric glacier shrinkage, gauging the magnitudes of not only the retreating area but also the lowering surface level is required. The rate of lowering of the glacier surface has been reported in Bhutan, thus far, only by Naito et al. (2006), who estimated it for a debris-free glacier, the Jichu Dramo Glacier from 1998 to 2003. The present paper reports the observational results of glacier shrinkages in Bhutan, including the surface lowering rates of two debris-covered glaciers and two debris-free glaciers, as well as repeated photo pairs showing terminal retreats of some other 2012 AIRIES

14 N. NAITO et al. debris-free glaciers. In addition to the global issue of sea level rise, glacier variations are related to local issues, too. Glacial lake outburst floods (GLOFs) are a crucial problem faced by regional countries and people in the Himalayas (Yamada, 1998; Ageta et al., 2000). Potentially dangerous glacial lakes usually grow on the terminal part of debris-covered glaciers (Yamada, 1998; Iwata et al., 2002), while the glaciers themselves shrink and moraines dam up the melt water. Expansion of the glacial lake is normally considered to be a result of glacier shrinkage. The present paper discusses the effect of glacial lakes upon glacier shrinkage, based on the observational results for two debris-covered glaciers. 2. Study Area and Methods The study area in the present paper is located in the northern part of Bhutan (Fig. 1), the so-called Lunana region, around the headwaters of the eastern branch of the Pho Chu (river). Several debris-covered glaciers and glacial lakes are closely distributed in the northeastern part of the area. Two debris-covered glaciers among them, the Thorthormi and Lugge Glaciers, are the present targets. An enlarged satellite image of them is shown in Fig. 2. A huge glacial lake, Lugge Tsho (lake), is located in front of the Lugge Glacier, while many relatively small supraglacial ponds are distributed on the debris-covered ablation area of the Thorthormi Glacier. Surface topography was surveyed on the ablation areas of the two glaciers each autumn in 2002-2004, using a total station system, the SOKIA SET 2000 series. Benchmarks for the topographical survey were set on the lateral moraine ridges as shown in Fig. 2. Locations of the surveyed points on the glacier surface were determined with a prism brought manually, though those of the terminal ice cliffs of the Lugge Glacier were surveyed by triangulation from two benchmarks on both lateral moraine ridges beside Lugge Tsho. In addition, bamboo stakes were installed on the glacier surface with a steam drill in 2002 and 2003. All the stakes were found to have fallen down due to considerable ice melting the next year, unfortunately. By surveying their root locations in 2003 and 2004, the surface glacier flow could be estimated. Thorthormi Gl. 2 km Lugge Tsho Surveyed line Benchmark Lugge Gl. Fig. 2 The two debris-covered glaciers studied in the present paper. The background is the same image as Fig. 1, enlarged. Fig. 1 Satellite image of the present study area; the Lunana region in the northern part of Bhutan. Blue and yellow dashed rectangles indicate the areas shown in Figs. 2 and 3, respectively. The background is an ALOS AVNIR-2 10 m mosaic image composited from captured data on Dec. 26, 2007 (right to central part) and Jan. 17, 2010 (left part) by Tadono et al. (2012). Fig. 3 The high plateau region, where many debris-free glaciers are distributed. Each number and letter attached to a glacier is explained in the text. The background is the same image as Fig. 1, enlarged.

Recent Glacier Shrinkages in the Lunana Region, Bhutan Himalayas 15 On the other hand, the southeast of the Lunana region (Fig. 1) is a high plateau area spreading around the boundary between the Pho Chu and Mangde Chu basins, where many debris-free glaciers are distributed. The enlarged satellite image covering this area is shown in Fig. 3. The surface topography of three debris-free glaciers was surveyed in the autumn of 2010, using portable GPS receivers, the Magellan Promark 3. The GPS measurements were post-processed using base station GPS data. The GPS survey was intended to be carried out as widely as possible on the glaciers, but bad conditions for receiving GPS signals and some mechanical troubles in the GPS receivers sometimes limited the measurements on part of the glaciers, unfortunately. Among the three glaciers, the Jichu Dramo Glacier had been surveyed before in 1998, 1999 and 2003. Another small glacier, numbered 1 in Fig. 3, had also been surveyed in 1999. The previous surveys on the two glaciers can be seen in Naito et al. (2006). The present paper describes the changes in these two debris-free glaciers. The other debris-free glacier surveyed in 2010 is indicated with the letter S in Fig. 3, and is expected to be surveyed in the future in order to evaluate its variation. In addition to the quantitative topographical survey, simpler observations of glacier variation were carried out by taking repeated photos. The present paper presents a comparison of the repeated photos for four representative debris-free glaciers, which are numbered 2-5 in Fig. 3. Repeated photos were also taken of other debris-free glaciers, indicated with the letter P in Fig. 3. Fig. 4 Longitudinal profile of the surveyed ogive bands along the upstream part of the longitudinal line on the ablation area of the Thorthormi Glacier, shown in Fig. 2. The abscissa is the longitudinal distance relative to the location of the cross-point with the transversal survey line of 2002, setting positive upstream. The thick dashed lines represent the linear regression of each year s profiles, the equations of which are also displayed. 3. Results and Discussions 3.1 Debris-covered glaciers 3.1.1 The Thorthormi Glacier A topographical survey was performed along one longitudinal and one transversal line on the ablation area of the Thorthormi Glacier, as shown in Fig. 2. The upstream part of the longitudinal line from its crossing point to the transversal line is bared with glacier ice, and a clear ogive has developed. Ten bands of the ogive were surveyed at the location of each ridge and trough. The longitudinal profile of the ogive bands is shown in Fig. 4. The regression lines for each profile represent the averaged surface levels. The surface uplifting upstream and lowering downstream in 2002-2003 cannot be considered significant, and thus no significant change in the surface level was confirmed for 2002-2003. A surface lowering of approximately 3 m, however, could be recognized in 2003-2004. Ultimately, the surface lowering rate on this part of the Thorthormi Glacier could be considered 0-3 m a -1 in 2002-2004. The horizontal flow speed was also estimated on the ablation area of the Thorthormi Glacier, as shown in Fig. 5. Three stakes that had been installed on the ridges of the ogive bands in 2002 were found in their downstream trough in 2003. Their locations in 2003 were corrected to the original ridges upstream. The accuracy of the modified speeds at the three stakes, thus, will be Fig. 5 Longitudinal distribution of the horizontal surface flow speed on the ablation area of the Thorthormi Glacier. The abscissa is the same as that in Fig. 4. lower than that at the other stakes. They are indicated by blank triangle marks in Fig. 5. The flow speed decreases downstream. Such a compressive flow is typical on ablation areas of glaciers and generates an upward emergence velocity. The above-mentioned surface lowering rate is a result of the compensation between this emergence velocity and surface ablation. 3.1.2 The Lugge Glacier A topographical survey was also performed on the ablation area of the Lugge Glacier, as shown in Fig. 2. As a matter of fact, the longitudinal survey line in Fig. 2 differed between 2002 and 2003. A bare-ice ridge extending downstream was surveyed in 2002; here it is tentatively called Ridge 1. Another bare-ice ridge at the left bank side of Ridge 1 was surveyed in 2003; its

16 N. NAITO et al. tentative name is Ridge 2. The two ridges are almost parallel with a transversal spacing of approximately 50 m. As both ridges were surveyed in 2004, the change in surface level can be evaluated on both. A longitudinal profile of the ridges is presented in Fig. 6 with all regression lines. A clear lowering can be found on both ridges. The surface lowering rates on these ridges turned out to be equivalent; approximately 5 m a -1. This rate is fairly large compared to that on the neighboring Thorthormi Glacier, 0-3 m a -1. The horizontal flow speed estimated on the ablation area of the Lugge Glacier is shown in Fig. 7. The flow speed is relatively uniform at roughly 40-55 m a -1. This result on the Lugge Glacier is contrastive to the clear compressive flow on the Thorthormi Glacier, seen in Fig. 5. The contrast in the glacier flow and shrinkage of the two glaciers is discussed below in subsection 3.1.3. The horizontal location of the terminal ice cliff of the Lugge Glacier was surveyed in 2002 and 2003. The survey results indicate a rapid terminal retreat of 30-50 m a -1. Considering the glacier flow speed of 40-55 m a -1 near the terminus, shown in Fig. 7, the calving rate from the glacier terminal cliff into Lugge Tsho is considered to be a very large value of 70-100 m a -1. 3.1.3 Feedback between glacier shrinkage and glacial lake growth Suzuki (2004) estimated ablation on the debriscovered ablation areas of both the Thorthormi and Lugge Glaciers through a heat budget calculation with meteorological data and surface temperatures captured from ASTER infrared imagery. His target areas of the ablation estimate included the longitudinal lines on both of the glaciers surveyed in this study. The results showed the ablation ranging from 5-8 m a -1, depending on the debris thickness, while the mean ablation was 6.8 and 6.9 m a -1 on the ablation areas of the Thorthormi and Lugge Glaciers, respectively. In short, regarding the surface mass balance averaged on the ablation areas of the two neighboring debris-covered glaciers, no significant difference could be recognized. On the other hand, regarding the surface lowering and the flow speed, they appear very contrastive, as mentioned above in subsections 3.1.1 and 3.1.2. This might be caused by the huge glacial lake, Lugge Tsho. If a huge glacial lake exists in contact with a glacier, the lake water could accelerate the basal glacier flow of the terminal part through buoyancy and/or lubrication effects. The terminal acceleration would weaken the compressive flow and emergence velocity. As a result, the surface lowering could be accelerated, because the weaker emergence velocity could cancel the smaller portion of net ablation. This hypothesis can be supported with the present results on the Lugge Glacier, in contrast to those on the Thorthormi Glacier. This means that a glacial lake could accelerate the thinning of the upstream glacier, although existence of the glacial lake itself has been normally considered to be the result of glacier shrinkage. Moreover, the glacier thinning could activate calving by relatively enhancing the Fig. 6 Longitudinal profile of the surveyed two ridges on the ablation area of the Lugge Glacier, shown in Fig. 2. The abscissa is the longitudinal distance relative to the location of the cross-point with the transversal survey line of 2002, setting positive upstream. The thick dashed lines represent the linear regression of each year s ridges, the equations of which are also displayed. Fig. 7 Longitudinal distribution of the horizontal surface flow speed on the ablation area of the Lugge Glacier. The abscissa is same as that in Fig. 6. Fig. 8 Hypothetical illustration of a feedback mechanism between glacier shrinkage and glacial lake growth, for explaining contrastive features observed in surface lowering and flow speed distribution between the ablation areas of the Thorthormi and Lugge glaciers.

Recent Glacier Shrinkages in the Lunana Region, Bhutan Himalayas 17 buoyancy effect. After all, there might be a positive feedback mechanism between glacier shrinkage and glacial lake growth, as illustrated in Fig. 8. The feedback would work until glacier detached itself from the lake. The initiation of the feedback might be related to the lake depth versus glacier thickness, but this is still unclear and makes further study desirable. 3.2 Debris-free glaciers 3.2.1 The Jichu Dramo Glacier The surface topography of the lower part of the Jichu Dramo Glacier is fairly wavy. Based on repeated topographical surveys conducted in 1998, 1999, 2003 and 2010, the locations of surface bumps on the lower part of the glacier are depicted in Fig. 9. Among the surface bumps surveyed in 2010, six bumps were recognized to have been surveyed before. These are indicated in Fig. 9 as solid symbols and their tentative names are given without parentheses. From their horizontal displacements, their horizontal velocities were calculated, as listed in Table 1. Generally, the horizontal speed decreases upstream to downstream, as usually seen in the ablation area of a glacier. The change in the speed compared to the previous result is not clear. The horizontal direction of the velocity is almost northward at 16 cardinal points, with the sole exception of the L2 bump moving to the NNW. The surveyed altitudes of the six bumps are then projected with respect to the northward distance relative to the C1 bump location in 1998, as shown in Fig. 10. Thick regression lines in Fig. 10 are obtained for the same four bumps in 1999, 2003 and 2010. The regression line lowered by 10.0 m upstream and 10.6 m downstream between 1999 and 2003. The average surface lowering rate was thus evaluated to be 2.6 m a -1 in 1999-2003. Similarly, surface lowering was evaluated to be 22.7 m upstream and 26.4 m downstream, the average rate of which was 3.5 m a -1 in 2003-2010. If regression is used for the bumps including C1 or C3, the surface lowering rates are evaluated to be a little different from the above-mentioned ones. Considering the differences are less than 0.2 m a -1, the present result on the surface lowering rate in 1999-2003 is consistent with the previous estimate of 2-3 m a -1 by Naito et al. (2006), although they were estimated for different combinations of bumps. Therefore, neglecting changes in the surface undulation, the surface lowering rate in the lower part of the Jichu Dramo Glacier is concluded to have been 3-4 m a -1 in 2003-2010, and it may have accelerated compared to 1998-2003. As a proglacial lake had been grown along the glacier terminus, the location of the glacier terminus could not be surveyed in 2010. The terminal retreat since 2003, unfortunately, could not be evaluated. Fig. 9 Horizontal location of the surveyed surface bumps on the lower part of the Jichu Dramo Glacier. Solid symbols indicate surface bumps surveyed more than twice. Their tentative names are the same as those by Naito et al. (2006), except for C3. Bump names in parentheses indicate bumps not surveyed in 2010. The six bumps without parentheses are analyzed in the present study. Table 1 Horizontal velocities of surveyed surface bumps on the Jichu Dramo Glacier. The names of bumps are same as those displayed in Fig. 9. The velocity is expressed as horizontal speed U and azimuth from the north HA. Name of The present results The previous results (Naito et al., 2006) bump U (m a -1 ) HA (deg.) period U (m a -1 ) HA (deg.) period C1 19.1 2.0 1999 2010 24.0 342.5 1998 1999 C2 8.3 356.6 2003 2010 8.3 0.5 1999 2003 C3 7.8 6.7 2003 2010 (no survey before 2003) L1 7.6 1.5 2003 2010 9.0 355.0 1999 2003 L2 4.5 329.5 2003 2010 4.2 321.5 1999 2003 L3 8.8 351.5 2003 2010 6.2 353.9 1999 2003 Fig. 10 Vertical and northward projection of the six surface bumps. The abscissa is the northward distance relative to location of bump C1 in 1998. The left side of the figure (southward) is upstream. The thick lines and equations represent the linear regressions for the four bumps that were surveyed three times, in 1999, 2003 and 2010. The thin ones are those for the five bumps including C1 and C3.

18 N. NAITO et al. 3.2.2 A small unnamed glacier southeast of Jaze La The surface topography of a small debris-free glacier southeast of Jaze La, designated number 1 in Fig. 3, was also surveyed in 1999 and 2010. Retreat and shrinkage of this small glacier can be easily confirmed at a glance, by comparing the photographs in Fig. 11. The lines surveyed in 2010 are superimposed on the contour map surveyed in 1999 in Fig. 12. The glacier terminus retreated by 46.4 m averaged transversely during the eleven years, that is, it had a retreating rate of 4.2 m a -1. The glacier surface was quite smooth as seen in Fig. 11, so that the surface altitude in 1999 at a point along the surveyed line in 2010 could be interpolated from two surveyed points nearby ( + marks in Fig. 12) in 1999. Using the interpolation, the surface lowering was estimated at 7 points as shown in Fig. 12 with green marks. As a result, the surface lowering was smaller upstream and larger downstream. The annual rate was calculated to be roughly 1-3 m a -1. On the other hand, the surveyed line in 2010 on the northern part of the ice divide was located a few tens of meters westward from that in 1999. As this part of the ice divide was fairly wide and flat, the probable ridge top was surveyed both in 1999 and 2010. Therefore, the surface lowering could be estimated on this part, too, with a negligibly small error from comparison of the surveyed altitudes in 1999 to the east and in 2010 to the west. The estimated results at four sites are shown with green arrows in Fig. 12. These results agree with the above-mentioned features of the distribution and range of the annual rates. 3.2.3 Glacier shrinkage confirmed from repeated photos Terminal retreats and/or thinning of four other debris-free glaciers, numbered 2-5 in Fig. 3, can be recognized by comparing more recent photographs with previous ones, as shown in Figs. 13-16, respectively. One glacier, designated number 2, has significantly thinned on the left side and its terminal retreat is clear on the right side in Fig. 13. In fact, the surveyed small unnamed glacier mentioned in the preceding subsection 3.2.2 is located in the opposite valley beyond the left col of a peak seen in the right half of the photo in Fig. 13. A second glacier, designated number 3, can be clearly recognized in Fig. 14 to have retreated and thinned in 1999-2009. A third glacier, number 4, retreated drastically and its proglacial lake expanded in 1984-1999, as shown in Fig. 15, as previously reported by Naito et al. (2006). This glacier has continued to retreat and shrink in the 21st century, but its rate seems to have become relatively moderate. Its terminus may detach from the proglacial lake in the near future. A fourth glacier, number 5, has shrunk, too, as seen in Fig. 16. The glacier tongue part on the right side has disappeared and the left part has thinned in Fig. 16. It would be highly desirable to develop and make practicable a convenient and precise method of photogrammetry for such remote glaciated fields in the future, in order to measure such glacier shrinkages easily. Fig. 11 Repeated photos of the small unnamed glacier southeast of Jaze La, designated number 1 in Fig. 3, taken from the base point in Fig. 12. The shot dates are Oct. 2, 1999 and Sep. 23, 2010. Fig. 12 Surveyed lines for the small unnamed glacier southeast of Jaze La, designated number 1 in Fig. 3; on the glacier (red dashed), terminus (red solid) and shoreline of the proglacial pond (blue). The background contour map was surveyed in 1999 (Naito et al., 2006). The altitude of the base point was revealed to be 5,269 m a.s.l. by static GPS measurement in 2010. The green values are the reduction in altitude (m) between 1999 and 2010 evaluated in the present study, while the accuracy of that in parentheses at the terminus is low due to bad conditions for receiving GPS signals.

Recent Glacier Shrinkages in the Lunana Region, Bhutan Himalayas 1984 2010 Fig. 13 Repeated photos of glacier number 2 in Fig. 3, taken from Jaze La. The shot dates are Oct. 8, 1984 (provided by Dr. Toshihiro Tsukihara) and Oct. 1, 2010. 1999 2009 Fig. 14 Repeated photos of glacier number 3 in Fig. 3. The shot dates are Sep. 30, 1999 and Sep. 24, 2009. 19

20 N. NAITO et al. Fig. 15 Repeated photos of glacier number 4 in Fig. 3, taken from Gangrinchemzoe La. The shot dates are Oct. 2, 1984 (provided by Dr. Toshihiro Tsukihara), Oct. 9, 1999 and Oct. 5, 2010. Fig. 16 Repeated photos of glacier number 5 in Fig. 3. The shot dates are Oct. 13, 1998 and Oct. 5, 2010.

Recent Glacier Shrinkages in the Lunana Region, Bhutan Himalayas 21 4. Concluding Remarks The present paper evaluated surface lowering rates on four glaciers in Bhutan and found 0-3 m a -1 on the ablation area of the Thorthormi Glacier in 2002-2004, approximately 5 m a -1 on the ablation area of the Lugge Glacier in 2002-2004, 3-4 m a -1 on the lower part of the Jichu Dramo Glacier in 2003-2010, and 1-3 m a -1 on the small unnamed glacier southeast of Jaze La in 1999-2010. These results are valuable because information related to volumetric shrinkage of glaciers in Bhutan has been limited so far. Contrastive results in the surface lowering and distribution of flow speed between the two debris-covered glaciers, the Thorthormi and Lugge Glaciers, have suggested a positive feedback mechanism between glacier shrinkage and glacial lake growth. It would be desirable to study this further in order to understand the expansion process of glacial lakes as well as the fluctuation mechanism of calving glaciers. The surface lowering rate of the Jichu Dramo Glacier in 2003-2010 seems to have accelerated from the previous estimate of 2-3 m a -1 in 1998-2003 (Naito et al., 2006). Such acceleration of glacier shrinkage should be carefully monitored to confirm it. Repeated photographs have been accumulated to show glacier shrinkage and retreat in Bhutan, several representative pairs of which are provided in the present paper. It would be advisable to develop and apply a practical photogrammetry in order to accumulate quantitative information on glacier shrinkage and retreat in the future. Acknowledgements We are deeply indebted to staff of the Department of Geology and Mines (DGM), Ministry of Economic Affairs, Bhutan, for their consideration and support for our field research activities. We thank all members who participated in field activities related to the present study for their assistance. We would like to express special gratitude to Dr. Koji Fujita for GPS post-processing, Dr. Takeo Tadono for providing ALOS AVNIR-2 images, and Dr. Toshihiro Tsukihara for providing the glacier photos taken in the 1980s. The manuscript was improved by useful comments from Prof. Teiji Watanabe and an anonymous reviewer. The field activities in 2002-2004 were financially supported by Grants-in-Aid for Scientific Research (Nos. 13373006 and 13573004) from the Japan Society for the Promotion of Science (JSPS). The field activities in 2010 were supported by the Japan Science and Technology Agency (JST) and the Japan International Cooperation Agency (JICA), under the Science and Technology Research Partnership for Sustainable Development (SATREPS). The data analysis in this paper was supported by a Grant-in-Aid for Scientific Research (No. 20540430) from JSPS. In addition, the present study has been motivated and encouraged for a relatively long time, especially by Profs. Yutaka Ageta, Shuji Iwata, Tomomi Yamada and Kouichi Nishimura, to whom we would like to express our sincere thanks. At last, we would like to express our sincere condolences on the death of Mr. Dorji Wangda, the former Director of DGM. Our research activities in Bhutan since 1998 would never have been accomplished without his considerations and efforts. References Ageta, Y. (1983) Characteristics of mass balance of the summer-accumulation type glacier in the Nepal Himalaya. Seppyo, 45 (2): 81-105. (in Japanese with English abstract) Ageta, Y., S. Iwata, H. Yabuki, N. Naito, A. Sakai, C. Narama and Karma (2000) Expansion of glacier lakes in recent decades in the Bhutan Himalayas, Debris-Covered Glaciers. IAHS Publication, 264: 165-175. Asahi, K. (1999) Data on inventoried glaciers and its distribution in eastern part of Nepal Himalayas. CREH Data Report 2 (1994-1998), Institute for Hydrospheric-Atmospheric Sciences, Nagoya University and Department of Hydrology and Meteorology, HMG of Nepal, 1-76. Eguchi, T. (1994) Regional differences in precipitation and the cause of dry valleys in the Bhutan Himalayas. Chapter 4 of Regional Differences in Precipitation in the Globe, the Indochina Peninsula and the Bhutan Himalaya, Doctoral thesis, the University of Tokyo, 111-167. Fujita, K. and Y. Ageta (2000) Effect of summer accumulation on glacier mass balance on the Tibetan Plateau revealed by mass-balance model. Journal of Glaciology, 46: 244-252. Fujita, K., M. Nakawo, Y. Fujii and P. Paudyal (1997) Changes in glaciers in Hidden Valley, Mukut Himal, Nepal Himalayas, from 1974 to 1994. Journal of Glaciology, 42: 583-588. Iwata, S., Y. Ageta, N. Naito, A. Sakai, C. Narama and Karma (2002) Glacial lakes and their outburst flood assessment in the Bhutan Himalaya. Global Environmental Research, 6: 3-17. Karma, Y. Ageta, N. Naito, S. Iwata and H. Yabuki (2003) Glacier distribution in the Himalayas and glacier shrinkage from 1963 to 1993 in the Bhutan Himalayas. Bulletin of Glaciological Research, 20: 29-40. Naito, N., Y. Ageta, M. Nakawo, E. D. Waddington, C. F. Raymond and H. Conway (2001) Response sensitivities of a summer-accumulation type glacier to climate changes indicated with a glacier fluctuation model. Bulletin of Glaciological Research, 18: 1-8. Naito, N., T. Kadota, K. Fujita, A. Sakai and M. Nakawo (2002) Surface lowering over the ablation area of Lirung Glacier, Nepal Himalayas. Bulletin of Glaciological Research, 19: 41-46. Naito, N., Y. Ageta, S. Iwata, Y. Matsuda, R. Suzuki, Karma and H. Yabuki (2006) Glacier shrinkages and climate conditions around Jichu Dramo Glacier in the Bhutan Himalayas from 1998 to 2003. Bulletin of Glaciological Research, 23: 51-61. Suzuki, R. (2004) Estimation on Glacier Melting in Lunana Region, Bhutan. Master thesis, Nagoya University. (in Japanese with English abstract) Tadono, T., S. Kawamoto, C. Narama, T. Yamanokuchi, J. Ukita, N. Tomiyama and H. Yabuki (2012) Development and validation of new glacial lake inventory in the Bhutan Himalayas using ALOS DAICHI. Global Environmental Research, 16: 31-40. Yamada, T. (1998) Glacier Lake and its Outburst Flood in the Nepal Himalayas. Monograph No. 1, Data Center for Glacier Research, Japanese Society of Snow and Ice.

22 N. NAITO et al. Nozomu NAITO Satoru YAMAGUCHI Nozomu NAITO is a Professor at the Hiroshima Institute of Technology. He has investigated glacier variations in the Himalayas since 1995, when he started his PhD course study at Nagoya University. He obtained his PhD in 2001, with a focus on numerical studies on recent glacier shrinkages in the Nepal Himalayas. He has joined field research teams studying glaciers and glacial lakes in Bhutan four times so far, in 1998, 1999, 2002 and 2010. Recently, his growing interest in the interaction between glacier shrinkage and glacial lake expansion in the Himalayas has led him to expand his scope to the flow and variations of calving glaciers in Patagonia, too. He was a member of the 34th Japanese Antarctic Research Expedition in 1992-1994. In addition to his research activities, he now works in education and providing support for diversifying students. Satoru YAMAGUCHI is a researcher at the Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Prevention. His present subjects of interest are snow physics and development of a snow cover model to forecast snow disasters, such as snow avalanches, snow drifts and so on. In addition, he has maintained a strong interest in glacier variations in the Himalaya region because his first glacier survey was in the Nepal Himalayas in 1995 and the theme of his doctoral thesis was glacier dynamics. Nowadays, using glacier fluctuation models, he is investigating the mechanisms of debris-covered glacier development: the critical conditions distinguishing clean-type glaciers from debriscovered glaciers, and what factors determine the surface inclination of debris-covered glaciers. Ryohei SUZUKI Takanobu SAWAGAKI Ryohei SUZUKI obtained his PhD in science from Nagoya University, Japan in 2007. His primary interest is in spatial distributions of thermal properties of debris cover on glaciers in the Himalayas, focusing on the relationship of such thermal properties to the ice melt rates under the debris covers, using a heat budget approach. He is also interested in applying image analysis techniques using optical and thermal remote sensing data and digital elevation modelling to glaciological studies. He joined field research teams studying glaciers and glacial lakes in Bhutan three times in 2002-2004. In addition, he participated in glaciological field research in Patagonia in 2004 and 2005. He is now engaging in the field of software engineering with Fujitsu Software Technologies Co., Ltd., taking a special interest in applications of image processing and computer graphics techniques. Jiro KOMORI Jiro KOMORI is a JICA expert on technical/ research cooperation in Bhutan, and holds an appointment as a Contract Assistant Professor at the Graduate School of Environmental Studies, Nagoya University. As a JICA expert, he has been dispatched to the newly established Division of Glaciology at the Department of Geology and Mines, Royal Government of Bhutan since 2009. Originally he worked for four years as an engineer at a geological consulting company and subsequently for four years at Nihon University as a laboratory assistant until 2000. He obtained his PhD in paleoenvironmental studies from the Graduate School of Tokyo Metropolitan University in 2005. As a graduate student, he also started to study subjects such as disaster prevention related to recent environmental change. His first field survey of glaciers and glacial lakes was in the Bhutan Himalayas in 2002. This brought an opportunity for precious experience and many encounters in Bhutan to not only himself but also his family. He currently has a keen interest and is seeking ways to disseminate the results of this research and educate the younger generation regarding the issues of environmental change rather than interest in the natural sciences. Yoshihiro MATSUDA Yoshihiro MATSUDA s main interest has been in glacier variations and the glacier surface energy balance in the Asian Highlands since 2001, when he entered the Graduate School of Environmental Studies, Nagoya University. He obtained his PhD from Nagoya University in 2008 through his research on numerical studies of climatic sensitivity of glaciers in the Asian Highlands. He has joined several glacier research teams in the Asian Highlands, and he participated field research teams on glaciers and glacial lakes in Bhutan in 2003 and 2004. Takanobu SAWAGAKI is an Assistant Professor of the Faculty of Environmental Earth Science, Hokkaido University. His major fields of study are Glacial Geology, Quaternary Science and Geographical Information Systems. He has broad experience in circumpolar and alpine regions as a member of Japanese Antarctic research expeditions, the Academic Alpine Club of Hokkaido, and his own research expeditions in cold regions around the world. Phuntsho TSHERING Phuntsho TSHERING is a geologist working in the Department of Geology and Mines, Ministry of Economic Affairs, Royal Government of Bhutan. He did his undergraduate work in the fields of Mathematics, Physics and Geology at the Post Graduate College of Science, Osmania University, India. One year after joining the department in 2008, he started working in the Glaciology Division and since then, he has been an active counterpart for a collaborative research project involving his department, JICA and JST. Working together with the JICA experts, he has been actively involved in implementing field activities along the northern glaciated frontiers of Bhutan in 2009, 2010 and 2011. Having been involved in such activities, he has a keen interest in specializing in the fields of environmental sciences and global climate change and its associated risks. Kharka Singh GHALLEY Kharka Singh GHALLEY is currently working as a Senior Geologist in the Glaciology Division, Department of Geology and Mines, Ministry of Economic Affairs, Royal Government of Bhutan. He earned his diploma in Mineral Exploration (Geology) from 1978 to 1980. He started his career in systematic geological mapping, mineral exploration, investigation of economic minerals and conducting expeditions in the higher Bhutan Himalayas. He attended the short-term training course on Geophysical Surveying for Ground Water Exploration at the National Geophysical Research Institute, Hyderabad, India in 1987. He undertook the 15th Post-Graduate Orientation Training Course organized by the Geological Survey of India at various training institutes/centers in 1990-1991 and completed the course with excellent marks. Since the establishment of the collaborative research project between DGM-JICA/JST he has been one of the active participants as a Bhutanese counterpart in the research project. He is closely associated with JICA short/long term experts; he has been constantly involved in implementing ground data collection works at the headwaters of the major river basins in the northern glaciated frontier region of the Bhutan Himalayas. (Received 30 November 2011, Accepted 13 February 2012)