The glacial retreat in the Himalayas after the Little Ice Age has so far produced the expansion o... more The glacial retreat in the Himalayas after the Little Ice Age has so far produced the expansion of some supraglacial ponds to a moraine-dammed lake on the tongue of each glacier. The lake expansion is probably accelerated by recent global warming. In order to clarify the mechanism of the lake expansion, the physics of three moraine-dammed lakes, Tsho Rolpa and Imja in Nepal and Lugge in Bhutan, was explored in 1996, 1997 and 2002, respectively. In spite of a similar wind system above the end moraine, wind-driven water circulation in the surface layer prevailed only in Tsho Rolpa Lake. For Tsho Rolpa, the end moraine is as high as the lake surface, while for Imja and Lugge, the upper dead-ice zone is 20 and 30 m higher, respectively, than the lake surface. The three-dimensional numerical simulation of airflow around Tsho Rolpa indicated that the 20-m heightening of the end moraine upwind of the lake decreases the wind velocity near the lake surface by 31%. It is noted that for decreasing the wind velocity, the rise of the end moraine is more effective than a decrease in the blowing distance with decreasing lake size.
Hydrological and meteorological observations of river runoff, precipitation and air temperature w... more Hydrological and meteorological observations of river runoff, precipitation and air temperature were conducted 27 August to 26 October 1982, in Langtang Valley, Nepal Himalaya, whereby the mass balance of the glacier system there was estimated. Observed values suggest that (1) all glacier ablation and rainwater in the subwatershed of Langtang Valley drain into the river with the runoff coefficient of 1; (2) ablation of the glacier system can be estimated simply using a degree-day factor of 10 mm/degree-day; and (3) precipitation is considered uniform over the whole watershed. Assuming that the suggested phenomena persist throughout the year, records of monthly precipitation and monthly mean temperature in this valley, indicate that annual accumulation and ablation in the glacier system amount to 2000 ± 200 mm, respectively.
The densification of water-saturated firn, which had formed just above the firn-ice transition in... more The densification of water-saturated firn, which had formed just above the firn-ice transition in the wet-snow zone of temperate glaciers, was investigated by compression tests under pressures ranging from 0.036 to 0.173 MPa, with special reference to the relationship between densification rate, time and pressure. At each test, the logarithm of the densification rate was proportional to the logarithm of the time, and its proportionality constant increased exponentially with increasing pressure. The time necessary for ice formation in the firn aquifer was calculated using the empirical formula obtained from the tests. Consequently, the necessary time decreased exponentially as the pressure increased, which shows that the transformation from firn in ice can be completed within the period when the firn aquifer exists, if the overburden pressure acting on the water-saturated firn is above 0.12–0.14 MPa. This critical value of pressure was in good agreement with the overburden pressure o...
To investigate the internal structure and transformational processes from firn to ice of the Hisa... more To investigate the internal structure and transformational processes from firn to ice of the Hisago snow patch on Daisetsu Mountain, Hokkaido, Japan, many drillings were made during the ablation period in 1986 and 1987. The ice cores were analyzed for stratigraphy, density and free water content. The internal structure of the snow patch was characterized by a wet firn layer with abundant ice layers and ice glands overlying a 4.3 m-thick ice body. The thickness of the firn layer varied from 12.7 m in June to 1.3 m in October. A water-saturated firn layer about 1 m thick existed just above the firn-ice transition. The annual layers were identified by dirt layers which showed that 1–2 m of ice was formed each year when the mass budget was positive. Although the densification of the water-saturated firn layer proceeded rapidly, the transformation from firn to ice could not be recognized during the ablation period. It was concluded that the formation mechanism of the ice body comprised t...
Proceedings of the 1996 International Snow Science Workshop Banff Canada, 1996
A severe storm struck the Nepal Himalaya on November 9 and 10, 1995. This storm was the most inte... more A severe storm struck the Nepal Himalaya on November 9 and 10, 1995. This storm was the most intense event to occur during the autumn in at least 50 years. The autumn season in the Himalaya tends to be quite dry, so this storm seemed extraordinary. Precipitation gages at lower elevations caught 50 to 200 mm of rain during the storm. Cold temperatures led to snowfall above 3,500 m in the Khumbu region of east Nepal, and snow depths increased rapidly with elevation. About 30-50 em of snow fell at 3,800 m; 50-100 em of snow was found at about 4,000 m; and 100-200 em of snow was deposited above 5,000 m. The intense snowfall generated numerous avalanches throughout the region. A few had tragic consequences. The worst incident occurred near the village ofPangkha in the Gokyo Valley where a crowded lodge was destroyed by an isolated avalanche. Twenty-four people were killed there. Seven other deaths resulted from an avalanche in the Kanchenjunga area of far eastern Nepal. Many other people were involved in non-fatal avalanche accidents. Hundreds of people were stranded by the deep snows and approximately 550 people were flown out of the snow zone by helicopters. At least 100 animals were lost by burial in the deep snows. Village life in the higher areas was disrupted through much of the winter. The residual deep snows resulted in another avalanche cycle in March as percolating melt water destabilized slopes.
The characteristics of precipitationdistribution, particularly with their temporal and spatial va... more The characteristics of precipitationdistribution, particularly with their temporal and spatial variations, were investigated by intensive observations around the Langtang Valley in the monsoon season. Also, the effects of cyclone activities, which are associated with hemispheric scale fluctuations of atmospheric circulation patterns, to the inter-annual variation of winter precipitation at Kathmandu are examined. Ken 'ichi Ueno et al.
November 24-25, 1971: It was confirmed that the snow surface at the observation site was higher b... more November 24-25, 1971: It was confirmed that the snow surface at the observation site was higher by 5 cm than the initial surface observed on October 26, 1971. November'26, 1971: A new accumulation of snow, 13 cm thick, was superposed on the previous surface of the snow cover. A fluctuation of the snow surface. by 5 cm in height took place by subsequent deposition and erosion, until the observation was over on January 13, 1972. According to such a variation of the level of the snow surface, the levels of the points of temperature measurement referring to the snow surface varied as follows: Periods Level of thermocouple (cm: referrin � to the snow surface) #1 #2 #1
Kita-ku, kpporo 060 ]Department ofA`techanical Ehgineering, ?VLrguoha Uitivensity of 1lechnotqgy,... more Kita-ku, kpporo 060 ]Department ofA`techanical Ehgineering, ?VLrguoha Uitivensity of 1lechnotqgy, Kbmitomioko-cho, IVtrgaeko 940-21 thtionat institute ofPolarResearch, 9-1O, Ktzga i-chome, ftabashi-ku, Tblya 173 Absttact: At Dome F, one ofthe summits ofthe East Antarctic Ice Sheet, a yery deep ice-conng operation is to be carried out by the Japanese Antarctic Research Expedition from 1995. Since it will take two years to complete the coring up to about 3ooO rn depth, the borehole should be fi11ed with proper drilling fluid to prevent borehole closure during the operation. This paper is a report on our investigations for searching for the proper dn1]jng fluid which can be used in the very cold environment at Dome F, Although the investigations are still in progress, three kinds of fluid were chosen as drMing fluid candidates. They are: 1) n-butyl acetate, 2) "IP-solvent" with densifier and 3) Silicone Oil. Their properties were investigated and compared in terms of density and viscosity, which are essential Tequirements for a drilling fluid. As a result, it was shown that n-butyl acetate and IP-solvent with densifier can be used as the dri11ing fluid. However. the use of n-butyl acetate is impossible without suthcient ventilation at the coring site or other action to dispose of its vapor. When the use of IP-solvent with densifier is considered, the choice ofproper densifier is also a problern.
Across the surface of debris-covered glaciers in the Nepal Himalayas there are many lakes on the ... more Across the surface of debris-covered glaciers in the Nepal Himalayas there are many lakes on the order of 1 km in scale. Some of the lakes, dammed by the end/lateral moraine, have been expanded from ponds on the order of 100 m in length. Tsho Rolpa Glacier Lake in the headwater region of the Rolwaling Valley, Eastern Nepal, was probably a small pond in the early 1950s. The present expansion rate of the glacial lake is unknown. From our investigation of the hydrological and meteorological conditions in 1993-1994, the calculated heat balance in the lake showed a deepening rate of about 1.2 m yr Ϫ1 all through the year. This is comparable to the mean deepening rate of the bottom basin since 1952. The vertical expansion thus is still continuing. Annual volume expansion including the calving ice (horizontal expansion) volume was 3% of the present total volume of the lake.
Supraglacial Tsho Rolpa Lake in the Nepal Himalaya has been increasing rapidly in size since the ... more Supraglacial Tsho Rolpa Lake in the Nepal Himalaya has been increasing rapidly in size since the 1950s, corresponding to the mountain-glacier shrinkage after the Little Ice Age. The lake basin expansion results from the subsidence by dead-ice melt below the bottom of the lake, and the retreat of the glacier terminus. Field observations of Tsho Rolpa in 1996 revealed that the retreat of glacier terminus is connected to a wind-induced vertical circulation of surface water heated by solar radiation. In order to clarify the mechanism of the lake expansion associated with sedimentary processes, we measured Ž. bottom sedimentation rate with some sediment traps, and vertical suspended sediment concentration SSC and water temperature, and analyzed the grain size of suspended and trapped sediments. The sediments, mostly composed of clay-sized grains, are dominantly supplied by glacier-melt water inflow at the glacier terminus. Sedimentary processes of such fine Ž. Ž. sediment comprise: 1 suspended-sediment fallout from intrusion of horizontal currents; 2 sediment sorting by sediment-Ž. Ž. Ž. laden underflows; and 3 the debris supply from the ice collapse at the glacier terminus. The 1 and 2 processes produce the density stratification of the lake, accompanied by a pycnocline at a depth of about 27 m. The existence of the pycnocline builds up the vertical water circulation in the surface layer to enhance the glacier-melt at the terminus. With respect to the subsidence of the lake bottom, nearly molecular thermal diffusion is probably dominant near the bottom of the deepest point, which results from the kinetic-energy dissipation of sediment-laden underflows. The stable existence of the bottom turbid water throughout the year could cause continuous dead-ice melt below the lake bottom.
In order to clarify the physics of basin expansion of a supraglacial lake, we investigated the me... more In order to clarify the physics of basin expansion of a supraglacial lake, we investigated the meteorology, hydrodynamics and basin topography in Tsho Rolpa Glacier Lake (27°51'N, 86°29'E : lake level, 4580 m above sea level ; length, about 3 km ; surface area, 1.39 km 2 ; maximum depth, 131 m) in the premonsoon season of 1995. Tsho Rolpa Lake has been expanded by a large recession of the glacier (the Trakarding Glacier) since 1950's, when it was about 1 km long accompanied by six closed ponds 100 to 200 m long. The rapid lake basin expansion accompanying the glacier recession is probably due to an increase of meltwater discharge from the global warming. Vertical and continuous measurements of water temperature and suspended sediment concentration (SSC) in the lake revealed that under the density stratification made up by large SSC, thermal conditions at the bottom are controlled by dynamic behaviors of sediment-laden underflows and wind-driven currents. The underflows were generated off a subaqueous mouth of englacial tunnels, which is located at the base of the cliff-shaped glacier terminus. The leeward transport of radiative heat by wind-driven currents is responsible for enhancing the ice carving at the glacier terminus ; a receding speed of the terminus was 18 cm/d on average in 1993-1994, being 280 times as high as the rate of lake-bottom subsidence, 0.064 cm/d at uplake of the terminal moraine.
The glacial retreat in the Himalayas after the Little Ice Age has so far produced the expansion o... more The glacial retreat in the Himalayas after the Little Ice Age has so far produced the expansion of some supraglacial ponds to a moraine-dammed lake on the tongue of each glacier. The lake expansion is probably accelerated by recent global warming. In order to clarify the mechanism of the lake expansion, the physics of three moraine-dammed lakes, Tsho Rolpa and Imja in Nepal and Lugge in Bhutan, was explored in 1996, 1997 and 2002, respectively. In spite of a similar wind system above the end moraine, wind-driven water circulation in the surface layer prevailed only in Tsho Rolpa Lake. For Tsho Rolpa, the end moraine is as high as the lake surface, while for Imja and Lugge, the upper dead-ice zone is 20 and 30 m higher, respectively, than the lake surface. The three-dimensional numerical simulation of airflow around Tsho Rolpa indicated that the 20-m heightening of the end moraine upwind of the lake decreases the wind velocity near the lake surface by 31%. It is noted that for decreasing the wind velocity, the rise of the end moraine is more effective than a decrease in the blowing distance with decreasing lake size.
Hydrological and meteorological observations of river runoff, precipitation and air temperature w... more Hydrological and meteorological observations of river runoff, precipitation and air temperature were conducted 27 August to 26 October 1982, in Langtang Valley, Nepal Himalaya, whereby the mass balance of the glacier system there was estimated. Observed values suggest that (1) all glacier ablation and rainwater in the subwatershed of Langtang Valley drain into the river with the runoff coefficient of 1; (2) ablation of the glacier system can be estimated simply using a degree-day factor of 10 mm/degree-day; and (3) precipitation is considered uniform over the whole watershed. Assuming that the suggested phenomena persist throughout the year, records of monthly precipitation and monthly mean temperature in this valley, indicate that annual accumulation and ablation in the glacier system amount to 2000 ± 200 mm, respectively.
The densification of water-saturated firn, which had formed just above the firn-ice transition in... more The densification of water-saturated firn, which had formed just above the firn-ice transition in the wet-snow zone of temperate glaciers, was investigated by compression tests under pressures ranging from 0.036 to 0.173 MPa, with special reference to the relationship between densification rate, time and pressure. At each test, the logarithm of the densification rate was proportional to the logarithm of the time, and its proportionality constant increased exponentially with increasing pressure. The time necessary for ice formation in the firn aquifer was calculated using the empirical formula obtained from the tests. Consequently, the necessary time decreased exponentially as the pressure increased, which shows that the transformation from firn in ice can be completed within the period when the firn aquifer exists, if the overburden pressure acting on the water-saturated firn is above 0.12–0.14 MPa. This critical value of pressure was in good agreement with the overburden pressure o...
To investigate the internal structure and transformational processes from firn to ice of the Hisa... more To investigate the internal structure and transformational processes from firn to ice of the Hisago snow patch on Daisetsu Mountain, Hokkaido, Japan, many drillings were made during the ablation period in 1986 and 1987. The ice cores were analyzed for stratigraphy, density and free water content. The internal structure of the snow patch was characterized by a wet firn layer with abundant ice layers and ice glands overlying a 4.3 m-thick ice body. The thickness of the firn layer varied from 12.7 m in June to 1.3 m in October. A water-saturated firn layer about 1 m thick existed just above the firn-ice transition. The annual layers were identified by dirt layers which showed that 1–2 m of ice was formed each year when the mass budget was positive. Although the densification of the water-saturated firn layer proceeded rapidly, the transformation from firn to ice could not be recognized during the ablation period. It was concluded that the formation mechanism of the ice body comprised t...
Proceedings of the 1996 International Snow Science Workshop Banff Canada, 1996
A severe storm struck the Nepal Himalaya on November 9 and 10, 1995. This storm was the most inte... more A severe storm struck the Nepal Himalaya on November 9 and 10, 1995. This storm was the most intense event to occur during the autumn in at least 50 years. The autumn season in the Himalaya tends to be quite dry, so this storm seemed extraordinary. Precipitation gages at lower elevations caught 50 to 200 mm of rain during the storm. Cold temperatures led to snowfall above 3,500 m in the Khumbu region of east Nepal, and snow depths increased rapidly with elevation. About 30-50 em of snow fell at 3,800 m; 50-100 em of snow was found at about 4,000 m; and 100-200 em of snow was deposited above 5,000 m. The intense snowfall generated numerous avalanches throughout the region. A few had tragic consequences. The worst incident occurred near the village ofPangkha in the Gokyo Valley where a crowded lodge was destroyed by an isolated avalanche. Twenty-four people were killed there. Seven other deaths resulted from an avalanche in the Kanchenjunga area of far eastern Nepal. Many other people were involved in non-fatal avalanche accidents. Hundreds of people were stranded by the deep snows and approximately 550 people were flown out of the snow zone by helicopters. At least 100 animals were lost by burial in the deep snows. Village life in the higher areas was disrupted through much of the winter. The residual deep snows resulted in another avalanche cycle in March as percolating melt water destabilized slopes.
The characteristics of precipitationdistribution, particularly with their temporal and spatial va... more The characteristics of precipitationdistribution, particularly with their temporal and spatial variations, were investigated by intensive observations around the Langtang Valley in the monsoon season. Also, the effects of cyclone activities, which are associated with hemispheric scale fluctuations of atmospheric circulation patterns, to the inter-annual variation of winter precipitation at Kathmandu are examined. Ken 'ichi Ueno et al.
November 24-25, 1971: It was confirmed that the snow surface at the observation site was higher b... more November 24-25, 1971: It was confirmed that the snow surface at the observation site was higher by 5 cm than the initial surface observed on October 26, 1971. November'26, 1971: A new accumulation of snow, 13 cm thick, was superposed on the previous surface of the snow cover. A fluctuation of the snow surface. by 5 cm in height took place by subsequent deposition and erosion, until the observation was over on January 13, 1972. According to such a variation of the level of the snow surface, the levels of the points of temperature measurement referring to the snow surface varied as follows: Periods Level of thermocouple (cm: referrin � to the snow surface) #1 #2 #1
Kita-ku, kpporo 060 ]Department ofA`techanical Ehgineering, ?VLrguoha Uitivensity of 1lechnotqgy,... more Kita-ku, kpporo 060 ]Department ofA`techanical Ehgineering, ?VLrguoha Uitivensity of 1lechnotqgy, Kbmitomioko-cho, IVtrgaeko 940-21 thtionat institute ofPolarResearch, 9-1O, Ktzga i-chome, ftabashi-ku, Tblya 173 Absttact: At Dome F, one ofthe summits ofthe East Antarctic Ice Sheet, a yery deep ice-conng operation is to be carried out by the Japanese Antarctic Research Expedition from 1995. Since it will take two years to complete the coring up to about 3ooO rn depth, the borehole should be fi11ed with proper drilling fluid to prevent borehole closure during the operation. This paper is a report on our investigations for searching for the proper dn1]jng fluid which can be used in the very cold environment at Dome F, Although the investigations are still in progress, three kinds of fluid were chosen as drMing fluid candidates. They are: 1) n-butyl acetate, 2) "IP-solvent" with densifier and 3) Silicone Oil. Their properties were investigated and compared in terms of density and viscosity, which are essential Tequirements for a drilling fluid. As a result, it was shown that n-butyl acetate and IP-solvent with densifier can be used as the dri11ing fluid. However. the use of n-butyl acetate is impossible without suthcient ventilation at the coring site or other action to dispose of its vapor. When the use of IP-solvent with densifier is considered, the choice ofproper densifier is also a problern.
Across the surface of debris-covered glaciers in the Nepal Himalayas there are many lakes on the ... more Across the surface of debris-covered glaciers in the Nepal Himalayas there are many lakes on the order of 1 km in scale. Some of the lakes, dammed by the end/lateral moraine, have been expanded from ponds on the order of 100 m in length. Tsho Rolpa Glacier Lake in the headwater region of the Rolwaling Valley, Eastern Nepal, was probably a small pond in the early 1950s. The present expansion rate of the glacial lake is unknown. From our investigation of the hydrological and meteorological conditions in 1993-1994, the calculated heat balance in the lake showed a deepening rate of about 1.2 m yr Ϫ1 all through the year. This is comparable to the mean deepening rate of the bottom basin since 1952. The vertical expansion thus is still continuing. Annual volume expansion including the calving ice (horizontal expansion) volume was 3% of the present total volume of the lake.
Supraglacial Tsho Rolpa Lake in the Nepal Himalaya has been increasing rapidly in size since the ... more Supraglacial Tsho Rolpa Lake in the Nepal Himalaya has been increasing rapidly in size since the 1950s, corresponding to the mountain-glacier shrinkage after the Little Ice Age. The lake basin expansion results from the subsidence by dead-ice melt below the bottom of the lake, and the retreat of the glacier terminus. Field observations of Tsho Rolpa in 1996 revealed that the retreat of glacier terminus is connected to a wind-induced vertical circulation of surface water heated by solar radiation. In order to clarify the mechanism of the lake expansion associated with sedimentary processes, we measured Ž. bottom sedimentation rate with some sediment traps, and vertical suspended sediment concentration SSC and water temperature, and analyzed the grain size of suspended and trapped sediments. The sediments, mostly composed of clay-sized grains, are dominantly supplied by glacier-melt water inflow at the glacier terminus. Sedimentary processes of such fine Ž. Ž. sediment comprise: 1 suspended-sediment fallout from intrusion of horizontal currents; 2 sediment sorting by sediment-Ž. Ž. Ž. laden underflows; and 3 the debris supply from the ice collapse at the glacier terminus. The 1 and 2 processes produce the density stratification of the lake, accompanied by a pycnocline at a depth of about 27 m. The existence of the pycnocline builds up the vertical water circulation in the surface layer to enhance the glacier-melt at the terminus. With respect to the subsidence of the lake bottom, nearly molecular thermal diffusion is probably dominant near the bottom of the deepest point, which results from the kinetic-energy dissipation of sediment-laden underflows. The stable existence of the bottom turbid water throughout the year could cause continuous dead-ice melt below the lake bottom.
In order to clarify the physics of basin expansion of a supraglacial lake, we investigated the me... more In order to clarify the physics of basin expansion of a supraglacial lake, we investigated the meteorology, hydrodynamics and basin topography in Tsho Rolpa Glacier Lake (27°51'N, 86°29'E : lake level, 4580 m above sea level ; length, about 3 km ; surface area, 1.39 km 2 ; maximum depth, 131 m) in the premonsoon season of 1995. Tsho Rolpa Lake has been expanded by a large recession of the glacier (the Trakarding Glacier) since 1950's, when it was about 1 km long accompanied by six closed ponds 100 to 200 m long. The rapid lake basin expansion accompanying the glacier recession is probably due to an increase of meltwater discharge from the global warming. Vertical and continuous measurements of water temperature and suspended sediment concentration (SSC) in the lake revealed that under the density stratification made up by large SSC, thermal conditions at the bottom are controlled by dynamic behaviors of sediment-laden underflows and wind-driven currents. The underflows were generated off a subaqueous mouth of englacial tunnels, which is located at the base of the cliff-shaped glacier terminus. The leeward transport of radiative heat by wind-driven currents is responsible for enhancing the ice carving at the glacier terminus ; a receding speed of the terminus was 18 cm/d on average in 1993-1994, being 280 times as high as the rate of lake-bottom subsidence, 0.064 cm/d at uplake of the terminal moraine.
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