Search

Glacier fluctuations during the Holocene in the Himalayas are compared with those in the world. Characteristics of glacier mass balance in the Nepal Himalaya, which belongs to the summer-accumulation type, are described. And the glacier fluctuations after the Little Ice Age in the Nepal Himalaya are discussed on the basis of variation of summer air temperature, which is the controling factor of glacier mass balance in this area.

A thermal drilling was carried cut in August of 1974 on the Khumbu Glacier flowing from Mt. Sagarmatha (English name Everest) in the East Nepal Himalayas. The drilling site was set at 5, 360 m above sea-level in the upper part of the ablation area of the glacier.The drilling was continued to a depth of 20.3 m where the drilling stopped due to the freezing of the drilled hole. Down to the depth, the relationship between the depth and the time of drilling was obtained, and the analysis of the results obtained showed that there were 7 layers down to a depth of 20 m. Three layers of them were ordinary glacier ice layers, three layers were blue ice layers or ice layers contaminated with dirt, and one layer corresponded to a vertically distributed ice layer containing air bubbles or a horizontally distributed ice layer containing water.A simple calculation of the freezing rate of the drilled hole showed that the ice temperature at a depth of 2 m was below -2°C at the time of drilling. The measurement of the resistance of a thermister put into the hole showed the ice temperature at a depth of 2.7 m was -5.3°C on 23rd November. Therefore, it was concluded that the distribution of ice temperature in the ablation area of the glacier might be of the polar type.

Observations of water discharge from a drainage area of 142.5 km2 including glacier zones were made at Dingboche (4330 m) in east Nepal. The annual discharge of this drainage was estimated as 1.7 × 108m3. The annual variation of the discharge showed a tendency to increase in summer and decrease in winter. It is assumed that precipitation during the monsoon season strongly contributes to high discharge in summer. On the basis of the data of ablation of glaciers and precipitation in this region, preliminary estimates of water balance in the drainage during a year were made. Since the variation of daily mean air temperature at Lhajung near Dingboche had a good correlation with the vatiation of daily discharge in summer but not in winter, the contribution of melt water from glaciers to the variation of the discharge was also discussed on the basis of the air temperature over glaciers estimated from the monthly mean temperature at Lhajung. Diurnal variations of the discharge in different months showed periodic tendencies which might be due to the diurnal variations of discharge of melt water from glaciers. The seasonal change of this tendency can be explained by the change of air temperature. Monthly discharge in depth of runoff from this drainage was compared with that at a point 460 m in altitude, in the lower part of this drainage. The latter was nearly twice as much as the former during the monsoon season, since precipitation in the upper drainage during the monsson season is less than below.

The oversnow traverse party of the Japanese Antarctic Research Expedition in 1985 found the location of the top of the second highest dome in the Antarctic Ice Sheet at 77°22'S, 39°37'E with an elevation of 3807 m, and surveyed the dome. A ridge of the ice divide runs from the dome top in a west-northwest direction, and a narrow subsurface basin lower than 500 m above the sea-level extends in a scale of 100 km long below the dome top in a similar direction to that of the surface ridge. In view of the larger scale of 100 km order on the subsurface topography, this dome is classified into "the subglacial basin type" in contrast with "the subglacial mountain type" such as Dome A, the highest dome in the Antarctic Ice Sheet. Comparative study between such types is important for discussions on the formation, development and variation of the ice sheet in the geological time scale, as well as their dynamics. From climatological and glaciological observations around the dome, the directions of prevailing winds and the lapse rates of snow temperature at 10 m depth (annual mean air temperature) are described, and the effect of the surface slope on such surface environments is discussed briefly. Annual mean air temperature at the dome top is estimated to be -58.0℃. By the use of mean annual net accumulation of 3.2 cm in water equivalent which was abtained from the 5 m-pit profile of tritium content near the dome top, age of the dome ice with depth is simply estimated.

This paper summarizes the studies of perennial snow patches conducted in the snow covered area of Japan during 1976-1978. Climatic and geomorphological characteristics of snow patches and the relationship between the changes in the size of perennial snow patches and climatic conditions are discussed in analysing whole data obtained through the studies. On the basis of studies carried out in 1976-1978, a format is proposed to describe general information of individual snow patch.

1985年に行った東クィーンモードランド氷床内陸部の調査により, その頂部Valkyrjedomenの最高地点(77°22′S, 39°37′E, 3807m)やその氷床表面形態が明らかになったほか, 雪の地球化学的特性がわかった。内陸に向かうにしたがい, 雪の電気伝導度は大きくなり, pHは低くなる傾向が認められたが, 特に標高3600m以上の内陸部でこの傾向が顕著であった。これは南極氷床内陸部では, 成層圏起源のエアロゾルやガスが, 雪の化学的特性を規定しているためと考えられる。, Glaciological observations on the high plateau in the East Queen Maud Land, Antarctica, were carried out along a route of the oversnow traverse, by the 25th and 26th Japanese Antarctic Research Expeditions in 1984 and 1985. The surface topography of the dome-like plateau (Valkyrjedomen, which is the second highest in Antarctica) and the positions of ice divides were determined clearly. The position and altitude of the highest place of the dome are 77°22′S, 39°37′E and 3807m a.s.l. Snow drift samples were collected along the route from Mizuho Station to Valkyrjedomen and were melted carefully in a snow vehicle. The value of electric conductivity of the melted snow samples at 0℃ was obtained before storing in the pre-cleaned bottles. In a home laboratory, pH measurements of the samples were carried out. It was revealed that the high electric conductivity and low pH values were found among the snow samples collected in the dome area, especially around the region higher than 3600m a.s.l. The region has the different glaciological characteristics from those in the katabatic wind region, that is, the lower degree of the surface inclinations, the lower net accumulation, the more smooth surface morphology, the lower ram hardness of surface snow layer and the higher lapse rate of snow temperature at 10m depth. Taking the comparatively higher concentration of artificial radio nuclides reported in the other Antarctic inland area into consideration too, the glacio-chemical environments in the Antarctic inland region are thought to be characterized by the transportation of the stratospheric aerosols or gases.

Observation of mass balance of Glacier AX010 at the southern front of the Nepal Himalayas was made from June to September in 1978. Since much of the annual accumulation due to the monsoon. and ablation occur simultaneously in the summer, the separate measurement of the amounts of accu mulation and ablation is difficult in this area. Accumulation is estimated from the precipitation on the basis of the relation between the probability of occurrences of solid precipitation ana surface air temperature, and ablation is obtained from the difference between the accumulation and the observational results of the balance. The probability of occurrences of solid precipitation had different linear relations with the air temperature between daytime and nighttime. The relation of air temperature to the estimated ablation is expressed by a power function. Although the change of accumulation depended on air temperature, the ablation was much more sensitive to the change of air temperature. The average summer balance over the whole area of the glacier was negative, but the positive summer balance in recent years is deduced. It is concluded that the fluctuation of the summer temperature on glaciers in the Nepal Himalayas under the influence of the summer monsoon is important for the variation of mass balance.

Observed sastrugi orientations showed considerable deviation from a bulk theory of katabatic wind in lee sides of troughs in ice sheet undulations of which the wavelength is about 400km on the Mizuho Plateau, East Antarctica. The effect of the inertia term which may account for the deviations but is often neglected in the equation of motion for katabatic wind is estimated with the perturbation method. A sinusoidally undulating slope with ridges and troughs is assumed for the model calculation instead of an infinite flat slope for the inertiafree model. The calculated results, in a typical inversion, suggest that the inertia term is significant if the wavelength of the undulations is smaller than about 200km while the effect of the undulations can be neglected if the wavelength is smaller than about 50km. Observed variability in the wind direction in the lee of the troughs may be accounted for by the effect of the inversion height which enhances the inertia effect.

The shape and size of snow crystals were recorded by making plastic replicas of them during the snowfall on April 23 and May 17, 1973, at Camp II (6470 m) along the climbing route to the summit of Mt. Yalung Kang (8505 m). It was found by observation of the photomicrographs of replicas that the shapes of snow crystals at 1705 NST, April 23, were hexagonal plates, crystals with broad branches, ordinary dendritic crystals and others, and that the time variation of crystals shapes during the period from 1000 NST to 1110 NST, May 17, was from plates to ordinary dendritic crystals through crystals with broad branches. In both cases, the altitudes of the tops of the precipitating clouds and the thickness of the cloud layer suitable for formation of snow crystals were estimated on the basis of experiments on artificial snow crystals.

Distributions of the glaciological and the meteorological aspects in Mizuho Plateau were plotted against the surface elevation of the ice sheet. Three boundaries common to most of the aspects were found at the elevations of 400-500m (firn line), 700-1000m (dry snow line), 1700-2100m and 3000-3200m. Glaciological zonation of the ice sheet in Mizuho Plateau was suggested. An estimation was made on the mass budget of the ice sheet in the Shirase and Soya drainage basins, Mizuho Plateau. Each mass budget appeared positive during the last several years. Approaches to determine the mass budget of the ice sheet were developed, and problems concerning its studies were pointed out.

Temperature in the ice layer of a glacier in the Nepal Himalaya was measured during the summer monsoon season in 1978, and at the end of March and in early September in 1979. It can be concluded from the subsequent alalysis that ice temperature in the upper part of the glacier increased with heat conduction, and was not affected by latent heat with the formation of superimposed ice. The annual mean temperature in the ice layer of the glacier was estimated to be in the range from -2.3°3 to -3.1°C in the region between the altitudes of 5007 and 5195 m, with a lapse rate of 0.47°C/100 m, so the glacier is of the polar type. The amount of superimposed ice formed in summer was estimated from a temperature profile to be 3.4 cm in water equivalent at an altitude of 5195 m.

Glaciological observations were made for the study of the glacier mass balance in the Nepal Himalayas, which is characterized by the simultaneous occurrence of considerable accumulation and ablation during the summer monsoon season. The upward change of the glacier surface level and the considerable amount of deposited snow due to the summer snowfall were observed at the end of summer over the whole area of the glaciers by means of stake measurements and stratigraphic observations respectively. On the other hand, the mass balance from July to September is calculated in consideration of the ice amount to be superimposed on the glacier ice of sub-zero temperature. The growth of the superimposed ice contributed to the positive mass balance in the upper-middle part of the glacier, while the mass balance during the same period was negative in the lower part. The total of the sum mer balance for the whole area of each observed glacier is concluded to have been positive. Such a positive summer balance is attributed mainly to the accumulation in late summer.

1969年11月～1970年1月の間に行なわれた第10次日本南極地域観測隊の内陸調査旅行のさい,昭和基地の東南東方向150km,南緯69°39',東経43°20',高度約1,600mの大陸氷床上に新しいモレーンが発見確認された.モレーンは直経数10mから数100mのものが3個,約N10°W方向に3kmの間に分布している.モレーンは巨視的に見て,谷地形の中に分布しており,東方は裸氷帯で,クレバスの多い急な登り斜面である.モレーンの礫は,亜角礫と角礫が大部分を占める.岩質は細粒片麻状閃緑岩が主で,桃色正長石花崗岩質の脈がよく発達しているものが多い.この種の岩石はリュツォ・ホルム湾沿岸ややまと山脈よりも,宗谷海岸北方に多い.モレーンの地形,氷,岩質の特徴から,モレーンの源は,現在の場所の比較的近くではないかと推察される.

The glaciological and meteorological observations were carried out on the perennial snow patch, named as “Hamaguri-yuki” at 2750m above ses level, in the cirque at Tsurugizawa of the Tateyama mountain range in the Central Japan (36°36'N and 137°37'E). The obtained results are as follows, 1) The area of the “Hamaguri-yuki” snow patch at the end of ablation season in 1967 was 4778m2 and its mass was 0.9 × 104 tons, that is, 1.3% of the mass at the beginning of ablation season, 67.5 × 104 tons.2) It was found by core drilling that the “Hamaguri-yuki” snow patch in 1967 consisted of three ice layers, the oldest of which was estimated as three years old. It can be said, therefore, that this snow patch once disappeared completely or nearly completely in 1964, after the observations were made on the same snow patch by the Toyama University Science Research Organization in 1963.3) The “Hamaguri-yuki” snow patch in 1967 could be divided into the accumulation area and ablation ares, the accumulation area ratio (AAR) being 0.54.4) Size of ice grains of the “Hamaguri-yuki” snow patch in 1967 was less than 1.5mm. It was found by the ice fabric studies that the crystallographic orientation of the principal axis of ice grains at the lowest part of the snow patch showed a tendency to concentrate in a direction parallel to the slope of ground at the base.

昭和基地南方約70kmの海岸にある露岩スカーレン(69°40'S, 39°25'E)の,東側と西側に流出する氷の流動速度を,1969年2月5日,10月12日および1970年2月4日の測量結果から算出した.測量は,スカーレンのふたつの基点から,氷の表面に立てた6本の標識ポールの位置を,ウィルドT2経緯儀で測角して求めた.これらの標識ポールは,海岸からの距離1～1.5km,高度140～160m,表面傾斜5～15°のところに設置した.えられた流速は,年間2～7mで,平均約4mとなり,今までに報告された南極氷床沿岸部の氷床の流速に比べてかなり小さい.これは,測定地点がスカーレンの露岩に近いところであったため,岩盤によって氷の流動が妨げられているからと考えられる.また,それぞれの標識ポールについて,2月から10月にかけての流速と,10月から翌年2月にかけての流速との間には,ほとんど差がみられなかった.

1969年12月,第10次日本南極地域観測隊の内陸調査旅行のさい,筆者らはやまと山脈南東,南緯71°50',東経36°15'付近の裸氷斜面上で隕石を9箇発見,採集した.これは,隕石採集を主目的として,計画的になされたものではないので,隕石の分布ひんどはかなり高そうである.この付近の地域や,類似の氷床の構造のところでは,今後も発見できそうである.採集された隕石はエコンドライト1箇,コンドライト8箇で,岩質からみて,少なくとも6種類(コンドライト5種,エコンドライト1種)の隕石である.

1967～69年に測定された,昭和基地周辺の一冬氷の氷厚と積算寒度(結氷日からの日平均気温の和)との関係から,海氷の成長に関する次の二つの経験式を導いた.北の浦:I=2.4√ オングル海峡:I=2.0√ ただし,Iは氷厚(cm),Σθは積算寒度(℃・day).

The characteristics and sensitivities of a cold-based glacier on the Tibetan Plateau, where the summer monsoon provides most of the mass input to glaciers, are discussed using an energy-balance model incorporating the process of water refreezing. The model accurately represents the observational results related to the mass balance of Xiao Dongkemadi glacier on the central plateau during 1992/93. Our data revealed that the mass balance of cold glaciers cannot simply be described by the surface mass/heat balances, because about 20% of infiltrated water is refrozen and thus does not run off from the glacier. Model calculations demonstrate that glaciers in an arid environment can maintain their mass since the monsoon provides precipitation during the melting season. Snowfall in summer keeps surface albedo high and largely restrains ablation. Nevertheless, the calculations also make clear that glaciers on the plateau are more vulnerable than those of other regions because of summer accumulation. In the monsoon climate, warming would cause not only a decrease in accumulation, but also a drastic increase in ablation in combination with surface-albedo lowering. Therefore, although glaciers on and around the plateau can be sustained by summer accumulation, they are more vulnerable to warming than winter-accumulation-type glaciers.

Glaciological observations on the high plateau were made along a route of the oversnow traverse by the 26th Japanese Antarctic Research Expedition in 1985. The shape of the domelike plateau (Valkyrjedomen), which is the second highest in Antarctica, and the position of ice divides have been known more than before. The highest place of this dome was found at 77°22′S, 39°37′E with an altitude of 3807m by the use of Navy Navigation Statellite System. The surface slope, net accumulation, configuration of snow surface, ram hardness, 10m snow temperature and others were observed. From these results, the characteristics of katabatic winds region were not found in the region higher than the altitude around 3400-3600m, which was about 400m higher than such altitude in the case of Mizuho Plateau. Surface slopes change to less than 2×(10)^ in the higher area from such altitudinal boundaries in both cases of the present study and Mizuho Plateau. From the observation of surface configuration, it was known that the directions of prevailing winds changed from southeast in the katabatic winds region to northeast around the highest place of the dome. On the basis of these results, patterns of atmospheric circulation over the plateau and its relation with the glaciological aspects are briefly discussed.

In November 1977, perennial snow patches were found at 1, 300 m in elevation at the north face of Mt. Daisen (1, 729 m, 35°22'N, 133°33'E) in Tottori Prefecture. Those are believed to be the southernmost perennial snow patches in Japan. It is considered that the snow masses could tide over a melting season, since concentrated snow deposits due to avalanches were covered with thick rock debris which restrain the ablation of snow.

Meteorological observations are made at Advance Camp (74°12′S, 34°59′E, 3200m above sea level) in East Queen Maud Land, Antarctica, from 7 February 1985 to 3 January 1986. The observations included those by a long-term unmanned weather recoder which operated from 1 March to 15 October 1985,with some interruption due to the extremely low temperature below -60℃. The total duration of data amounted to 10 months for the air temperature and 8 months for the wind speed and direction. The annual mean temperature and wind speed are -43.6℃ and 8.2m/s, respectively, which are estimated from the temperature difference from and the wind speed ratio to those at Mizuho Station. The wind direction constancy (W. SCHWERDTFEGER : Weather and Climate of the Antarctic, Amsterdam, Elsevier, 261p., 1984) is as high as 0.93 perhaps because of the steep slope (2.7×(10)^) in spite of the high altitude. We conclude that this new station is located in the Cold Katabatic region (P. C. DALRYMPLE : Antarctic Meteorology, ed. by M. J. RUBIN, 195,1966 (Antarct. Res. Ser., 9)). Concentrated observations including low-level soundings with radiosondes and pilot balloons are carried out in November and December. Wind spirals up to 2000m above the ice surface indicated that the wind in the free atmosphere influences strongly the surface wind and that the role of surface inversion is rather small. The surface wind system in the summer seems to be strongly affected by the synoptic pressure systems. The importance of diurnal activities is also made clear. The height of a diurnal mixing layer reaches about 400m and the strength of a blizzard is observed to be amplified on the plateau perhaps because of the instability of the surface layer.

A glaciological research project in east Queen Maud Land, Antarctica, has been carried out by the Japanese Antarctic Research Expeditions between 1982 and 1986 (JARE-23 – JARE-27). In this paper, we deal with the area traversed by JARE-25 and JARE-26, a representative inland plateau in Antarctica. In 1984, a team from JARE-25 extended a route from Mizuho Station (MS) to an advanced camp (AC; 74°12′S, 34°59′E; 3200 m a.s.l.) and returned to MS via the Yamato Mountains region. In the following year, 1985, a team from JARE-26 reached the summit (77°22′S, 39°37′Έ; 3810 m a.s.l.) of an ice dome on the plateau behind AC and continued to Asuka camp, north of Sør-Rondane Mountains. Investigations were carried out along the routes as follows: Geomorphological observations: the altitude along the routes was measured, together with the depth of the bedrock, which was obtained by radio echo-sounding. The shape of the dome and the position of ice divides were revealed. Gravity soundings were also carried out along the routes. Depositional and erosional environments of the snow surface: the net accumulation rate was obtained along the routes by the stake method. Sastrugi orientations were recorded in order to gain information on the prevailing wind. At several points, vertical profiles of snow stratigraphy and snow hardness were obtained, together with snow temperatures at 10 m depth. The glaciological characteristics of the plateau are described with reference to these results. Snow chemistry: the values of the electro-conductivity and pH of melted snow along the routes were obtained, and the results show high conductivity and low pH values around the dome region. Quantitative studies on the chemical composition of the samples are continuing. Ice coring: at the dome camp (DC; 77°00′S, 35°00′E; 3760 m a.s.l.), coring was carried out to a depth of 40 m. In the samples, we have been studying the vertical distribution of δ18O and the products of nuclear fission, in order to determine the accumulation rate and the atmospheric environment. On the basis of the results described above, the relationship between meteorological and glaciological conditions in the inland plateau are discussed.

Surface snow samples from the inland high plateau, East Queen Maud Land, Antarctica, show unique chemical characteristics. They are characterized by high acidity accompanying the high electrical conductivity, so that the hydrogen ion is the dominant ion, coupling with chloride and nitrate ions. The chemical composition differs sharply from sea salts. These characteristics appear more clearly than previously reported in Antarctica and are most strongly developed in snow samples from the high region. The tritium content increases in the inland high area, especially in the region higher than 3600 m asl (above sea level), which corresponds to the region where the effects of katabatic wind have vanished in the glaciological observations. The highest tritium content occurs in the vertical profile at a snow pit (3761 m asl, 77°00′S, 35°00′E), which corresponds to the snow deposition in 1966. The concentration is the highest ever reported in Antarctica and is almost as high as the one observed in the precipitation in the inland region of North America, which is the highest value ever reported in the world. All the results suggest that most of the ions contained in snow samples from the inland high plateau, especially higher than 3600 m asl, are not brought directly through the troposphere from the sea around Antarctica but from the higher atmosphere and that they are under the influence of the physicochemical reactions occurring there.