World Glacier Inventory - Inventaire mondial des Glaciers (Proceedings of the Riederalp Workshop, September 1978; Actes de l'Atelier de Riederalp, septembre 1978): IAHS-AISH Publ. no. 126,1980.

Present and late Pleistocene equilibrium line altitudes in the Mt Everest region — an application of the glacier inventory

F. Mùller

Abstract. UNESCO's pilot glacier inventory of the Mt Everest area was extended to include some 450 glaciers. After evaluation of various methods to establish the ELA, the pattern of the ELA isolines was analysed in relation to the orography, precipitation and temperature. The dominant role played by precipitation is recognized, and the unusually low mean AAR value of 0.41 is explained. Based on the assumption that the elevations of the numerous empty cirques in the area represent the ELA at the time of their formation, a map and subsequently a comparative SSW- NNE profile of present and late Pleistocene ELAs was constructed. The difference between the two curves, only 100 m at the main crest and almost 600 m at the southern end, must be attributed, in part, to differential uplifting of the Mt Everest area. After making allowance for this effect, the late Pleistocene temperature depression was estimated to be 4-5 C on the monsoon-affected Indian side and 2-3°C near the main mountain crest. It is concluded that the present pattern of monsoonal moisture supply also existed during late glacial times. Glaciation in the late Pleistocene was - as it is today - small in comparison to that of the other ice-prone parts of the globe.

L'altitude actuelle de la ligne d'équilibre et celle de la fin du pleistocene dans la région du Mt Everest — une application de l'inventaire des glaciers Résumé. L'inventaire-pilote des glaciers de la région du Mt Everest, effectué par FUNESCO, a été poursuivi et compte actuellement 450 glaciers. Après avoir étudié diverses méthodes permettant la détermination de l'altitude de la ligne d'équilibre (ELA), on a procédé à l'analyse du réseau des courbes de même ELA en rapport avec l'orographie, les précipitations et la température. On a mis en évidence le rôle primordial des précipitations et expliqué la valeur particulièrement basse de l'AAR moyen, qui est de 0.41. En partant de l'hypothèse que l'altitude des nombreux cirques dépourvus de glace de la région considérée représente l'ELA à l'époque de leur formation, on a établi une carte puis un profil comparatif SSW - NNE de l'ELA actuelle et de celle de la fin du pleistocene. L'écart entre les deux courbes, qui est de 100 m seulement aux abords de la ligne faîtière et de près de 600 m à l'extrémité sud, doit être attribué en partie aux différences d'amplitude des mouvements verticaux de la croûte terrestre dans la région du Mt Everest. Compte tenu de ce phénomène, l'abaissement de la température à la fin du pleistocene est estimé à 4-5°C sur le versant indien affecté par la mousson et à 2-3°C dans la région des principales crêtes montagneuses. On en déduit que la répartition actueËe des précipitations dues aux moussons existait également durant les époques glaciaires écoulées. La glaciation de la fin du pleistocene - autrefois tout comme de nos jours — était de faible étendue en comparaison avec les autres régions englacées du globe.

INTRODUCTION

The steady state equilibrium line altitude (ELA), closely related to the mean elevation of the firn line or snow line (in German: Altschneelinie, Schneegrenze), is considered an integrated climatic indicator. The integration encompasses both a series of climatic elements and several orographie-topographie effects. Painstaking efforts have been made to construct maps of the ELA or the firn line elevation for many glacierized parts of the world: Meier and Post (1962) and Péwé and Reger (1972) for northwestern North America; Andrews and Miller (1972) and Miller et al. (1975) for the Canadian Arctic; Millier et al. (1976) for the Swiss Alps; Messerli (1967) for the Mediterranean area; Grosswald and Kotlyakov (1969) for the USSR; Wissmann (1959) and Shi Ya-feng et al. (1979) for the Himalayas and Central Asia.

75

76 F. Mûller

The glacier inventories, now being compiled for many regions of both hemispheres, provide data for further and improved ELA maps which will, hopefully, permit a global overview. Furthermore, the regional ELA trend surface of the present glaciers may serve as a reference level for ELA maps depicting past and future glaciations. As an example, the Austrian glacier inventory, which contains data regarding glacier extent and ELA for both the present time and the '1850' stage, is cited (Patzelt, 1980).

In this paper the ELA of the present glaciers in the Mt Everest area is compared with that of the late Pleistocene ones, in order to speculate on the climatic change during this time span in the world's highest mountain range. A more comprehensive physiographic investigation of the region was carried out in connection with the Swiss Mt Everest Expedition 1956 (Mùller, 1958/1959). During a period of eight months the author had the opportunity to collect glaciological and climatological data on the glaciers of the Imja Khola basin, and to a lesser degree in the Dudh Kosi and Bhote Kosi basins (Fig. 1). The generous support of the Swiss Foundation for Alpine Research, the Canton of Zurich and the Swiss Nationalfonds is gratefully acknowledged.

THE PRESENT ELA

The pilot study A partial glacier inventory of the Mt Everest area was compiled as a pilot project (Muller, 1970) to test the applicability of the UNESCO guide (UNESCO/IAHS, 1970) for the Eastern Himalayas. The topographical maps of Schneider (1957,1965), at the scales 1:25 000 and 1:50 000 with contour intervals of 20 and 40 m respectively, depict the 1649 glaciers included in the study. A large number of expedition photographs, both single and panoramic, as well as Schneider's 1955-1963 terrestrial photogrammetric pictures were utilized.

Extension of the data base Additional data were compiled from: the Schneider 1965 map, the 'Mt Everest Region' maps of the Royal Geographical Society (1961 and 1975, scale 1:100 000) and a large collection of expedition photos from various archives. Glaciers to the north and the east of Mt Everest as well as some units to the south of the pilot study area were now included (Fig. 1). To record the additional 287 glaciers (bringing the total number of units on file to 451), the identification system developed by Muller (1970, Fig. 21) was used. By this expanded study a consistent and uniform data base for analysis was achieved. The material serves for comparison with the detailed glacier inventory work recently carried out in these areas by Chinese and Japanese glaciologists (Academia Sinica, 1975, inventory of 217 glaciers in Appendix, pp. 191-202; Lanchow Institute of Glaciology, Cryopedology and Desert Research, 1975; Higuchi et al, 1976; Watanabe, 1976; Fujii and Higuchi, 1977; Higuchi et at., 1978; Higuchi, et al, 1980.

Methods of assessing the ELA The assessment of the ELA for the glaciers of the Mt Everest region posed considerable difficulties, as direct observations were sparse, in consequence indirect means had to be used extensively. Gross et al (1977), in evaluating the most frequently used methods of establishing the ELA for areas where no, or few, mass balance measurements are available, found that the method suggested by Lichtenecker (1938) achieves the most reliable results. The position of the ELA is assessed by the highest elevation of occurrence of morainic material on the surface and along the margins of the glaciers. This procedure was already applied to some Karakoram glaciers by Visser (1938). For glaciers with large, high-lying accumulation basins and/or steep surface gradients near the equilibrium line, however, the resulting ELA values may be too low. Field observations established the ELA of the Khumbu Glacier at 5720 m a.s.L, whereas the

Equilibrium line altitudes in the Mt Everest region 77

lichtenecker value is only 5580 m. Nevertheless, independent tests showed that for most valley glaciers in the Everest area the Lichtenecker method gave reliable ELA data and was, therefore, utilized whenever possible. The high quality of the maps and photographs available for the area enhance the accuracy of the technique.

The Hess (1904) contour line method was also employed, either to independently establish the ELA of valley and cirque glaciers, or as a check. It assumes the ELA to be located at the change-over from convex (ablation area) to concave (accumulation area) contour lines. Unfortunately, in the Mt Everest region, the extremely steep and large headwalis and sidewalk of many valley glaciers contribute large amounts of avalanche snow to the accumulation area, causing frequently very irregular surface contours, and thus irregular firn lines. This factor, together with the often complex topography of the glacier bed, limited the application of the Hess method to simple cirque glaciers.

For the numerous glaciers not falling into the categories of valley or simple-shaped cirque glaciers, the Wafer (1879) and the related bergschrund methods were tried. An approximate ELA is calculated as the arithmetic mean of the elevation of the glacier tongue and the average elevation of the ridge/or respectively the bergschrund, surrounding the accumulation basin. The criticism levelled at these two methods by Gross et al. (1977) is certainly justified. Nevertheless, when cautiously applied to small simple-shaped mountain glaciers, they may still produce useful ELA data for strongly mountainous areas such as the Mt Everest region, where this type of glacier is common.

The Kurowski (1891 ) method must be viewed with even greater reservation. In the commonly used simplified version, the snow line is identified as the separation between equal areas of accumulation and ablation, i.e. an AAR of 50 per cent. The underlying assumptions are linear ablation and accumulation gradients and a symmetrical hypsographic curve. The glaciers of the Mt Everest region rarely fulfil these conditions. The AAR values of individual glaciers were found to range from 0.00 to 1.00, i.e. there are glaciers with no accumulation area, e.g. entirely fed by avalanches, as well as glaciers with no proper ablation area, e.g. losing ice only by avalanching over cliffs high enough to prevent reconstruction of the glacier at the foot of the wall. In fact, the data reported by Mulier (1970) and the discussion in the following two sections indicate that none of the fixed ratio methods, i.e. assuming the ratio of accumulation area (Sc) to ablation area (Sa) to be constant, are suitable for establishing the ELA for individual glaciers in this area. At best they may be used for a rough snow line assess­ment for a larger region if the AAR values for a few glaciers are known.

As the Hôfer and bergschrund methods also apply fixed rules irrespective of glacier type, they must be rejected for general application unless some mass balance data are available for the area.

Influence of orientation and orography (Table 1) Some characteristic glacier parameters such as tongue elevation, maximum length, total area and AAR value are tabulated for eight compass directions for the basins of the Nangpo, Dudh Kosi and Imja Khola, in order to assess the relative importance of orientation and orography. The number of valley glaciers for some orientation classes may be too small to yield meaningful results. The differences between the various orientations are generally quite large, though the patterns may not always be evident or consistent.

The highest mean tongue elevations, occurring in the south and southeast directions, are some 300 m higher than the lowest ones, found to face north and northwest, in spite of the predominantly southern direction of the main valleys in the area, thus testifying to the high effectiveness of the radiation. The fact that the largest glaciers (in length and area), most of which belong to the valley glacier type, face

78 F. Mûller

Mouniom peohs over 6500 «•

FIGURE 1. Identification scene for the glaciers of the Mount Everest region.

Equilibrium line altitudes in the Mt Everest region 79

SOURCES

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Research Scheme Nepal Himolaya 1965

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Royal Geographical Society, 196! , 1975

80 F. Mûller

TABLE 1. Elevation of glacier tongues in m a.s.l. (a), maximum length in km (b), total area in km2 (c), and AAR values in per cent (d) for different orientations: (A) for 60 glaciers in the Imja Khola basin, (B) for 162 glaciers in the three basins of the Nangpo Tsangpo, the Dudh Kosi and the Imja Khola and (C) for the 29 vaEey glaciers in the three basins. « = number of glaciers, x= mean value, s = standard deviation

N

NE

E

SE

S

sw

w

NW

« X

s

n X

s

n X

s

n X

s

n X

s

n X

s

n X

s

n X

s

X

s

A Imja Khola basin all glaciers, n = 60

a

4980 ±310

5130 ±400

5090

5250 ±150

5300 ±240

5080 ±100

5160 ±180

4860 ±400

valley

b c

n = 11 1.9 1.7

« = 6 1.8 1.2

« = 3 1.0 0.3

« = 11 2.7 2.3

« = 7 2.9 1.9

« = 5 3.0 3.8

n = 6 5.6 9.4

« = 11 1.9 1.2

d

0.52 ±0.23

0.50 0.23

0.44

0.43 ±0.16

0.36 ±0.21

0.41 ±0.06

0.43 ±0.21

0.35 0.15

B Nangpo, Dudh and Imja all glaciers, « = 162

a

5050 ±290

5110 ±330

5120 +290

5280 ±190

5230 ±300

5210 ±190

5210 ±150

4970 ±370

glaciers, all directions

b c

« = 18 1.6 1.3

« = 18 1.5 0.9

« = 2 5 1.9 1.3

« = 23 2.5 1.8

« = 24 3.8 5.6

« = 14 2.5 2.5

« = 24 2.0 2.5

« = 16 1.5 0.9

d

0.50 ±0.20

0.47 0.23

0.40 0.12

0.35 0.21

0.41 ±0.20

0.35 ±0116

0.42 ±0.23

0.37 ±0.14

C Nangpo, Dudh and Imja valley glaciers* n = 29

a

4800

4840

4840

5140 ±130

4850 ±210

4960

4940

4660

4910 ±250

b

n = 2 4.5

rc = 3 4 .2

n = 4 4.5

n = 6 4.9

n = l 10.1

n = 2 9.6

n = 3 11.0

n = 2 2.7

6.8

c

4.7

2.7

3.9

4.4

18.0

12.9

18.7

1.8

9.4

d

0.45

0.27

0.38

0.29 0.14

0.38 ±0.10

0.37

0.46

0.43

0.37 0.13

* Only glaciers larger than 2 km in length and 1 km2 in area are included.

southwards (in the Imja basin westwards) must be attributed to both the orography and the predominantly southern and southwestern origin of the precipitation.

The highest mean AAR values, amounting to about 0.50, occur on glaciers with a northeastern or northern aspect, while south facing glaciers usually show mean AAR values of less than 0.40. The large standard deviations for the values in Table 1 (as well as in Table 2) are a measure of the great variety of orographic and climatic conditions in the area. Some of the data sets have strong skewness or are bimodal, in particular those for the size parameters. Shortcomings in the interpretation of the photos and maps and/or in the assessment methods may also have increased the standard deviations and may, through systematic errors, even have shifted the mean values.

AAR and ELA for different glacier types (Table 2) The AAR values obtained for valley and cirque glaciers are clearly lower than those for the remaining glacier types. This observation applies for all three basins. It may be explained as a result of the especially strong avalanche nourishment of those glacier

Equil ibrium line altitudes in the Mt Everest region 81

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types and by the ice-preserving influence of the frequently extensive debris cover. The headwalls of many cirque and valley glaciers form the steepest, occasionally overhanging, sections of this high mountain.

Of particular interest is the surprisingly low mean AAR value of 0.41 for the entire area. Meier and Post (1962, p. 73) maintain that glaciers in dynamic equilibrium have an AAR value of about 0.60. Gross et al. (1977, p. 230) conclude from the mass balance data collected so far on the six best known glaciers in the Alps that steady state AAR values vary between 0.60 and 0.68, and, therefore, they apply a rounded 5c /5a ratio of 2:1 for their investigation. Mass balance measurements made over the last 18 years on the White Glacier in the Canadian High Arctic (Millier, unpublished data) indicate a steady state AAR value of 0.75. Because of the particular topography in the Mt Everest region (extremely large and steep rock walls surrounding the accumulation basin and sometimes even towering along the ablation area) and because of the resulting specific type of nourishment a lower than usual steady state AAR value of perhaps 0.50 may be correct. The even lower mean value of 0.41 calculated for the 1950s and early 1960s status of the glaciers may be attributed to the marked shrinkage at that time. Higuchi et al. (1980) report that also during the period ' I960' -1975,90 per cent of the debris-free glaciers in the area experienced a retreat.

The small differences (only a few tens of metres) between the mean ELA values of various glacier types established by different methods add support to the unusually low steady state AAR values. This, then, may mean that the AAR value of 0.60 ± 0.10 applied by Porter (1970) in the evaluation of Pleistocene glaciers in Swat Kohistan, West Pakistan, is too high, i.e. the resulting Pleistocene ELA is too low, and thus the climatic change is over-estimated. Indeed, in the light of the evidence presented here, Porter's Pleistocene ELA 'depressions' for West Pakistan of 3600, 3300 and 3000 ft respectively seem too large.

The 'I960' ELA map The modern ELA distribution in the Mt Everest region is so complex that, for the time being, the construction of a mathematical trend surface and the subsequent analysis of the residual values, as carried out for the Swiss glaciers (Mûller et al, 1976), is not advisable. Instead, a conventional cartographic solution (Fig. 2) was used to depict the 'I960' situation of the ELA. Though the interpretation may be difficult, it seems to offer more insight than a trend surface map or the mean values and their standard deviations, listed in Tables 1 and 2. The feature most clearly emerging from this map is the general rise of the ELA values from 5200 m on the southern mountains to the main range, and beyond to a dome-shaped culmination north of Mt Everest, and east of the Rongbuk Glacier, where a maximum elevation of 6300 m is reached. Northwards from there into the Tibetan Plateau, as well as to the east and the west, slight decreases are noticed.

Discussion of the present-day ELA The undulating ELA surface represented by the isolines of Fig. 2 is mainly determined, as for any area, by temperature, precipitation and topography.

The influence of precipitation and topography The general trend of the ELA in the northern hemisphere (decrease from low to high latitudes) is reversed in the Mt Everest region. Already Humboldt (1844) noticed this anomaly from snow line observations carried out by Webb, an Englishman, in 1816, further west in the Himalayas. A rise of 1100 m from the southern (Indian) to the northern (Tibetan) slope was reported, which coincides with the present-day rise in the Mt Everest area. These observations point to the great importance of the role played by precipitation on the glacierization of the Himalayas. In particular, the ELA

Equilibrium line altitudes in the Mt Everest region 83

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5B00

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FIGURE 2. Equilibrium line altitudes (ELA) in the Mt Everest region.

84 F. Mùller

culmination in the East Rongbuk Glacier area appears to result from the rain shadow effect of the Everest massif itself. The influence of temperature and radiation on mass balance, and thus on the ELA, seems in this area to be secondary to that of precipitation.

Table 3 represents a summary of the sparse data available on precipitation and temperature for a north-south transect. Differences in locality, time and method of observation make the data not strictly comparable. Nevertheless, a main pattern of precipitation distribution emerges, which coincides well with that of the present-day ELA. There is a general decrease of precipitation from low-lying southern to elevated northern stations. This tendency may be attributed to the depletion of the summer monsoon air masses. In the Khumbu Himal 75 to over 80 per cent of the precipitation falls during the monsoon period, which regularly starts at the beginning of June and ends in mid-October. The long time span from mid-October to late May is characterized by generally fair weather with only occasional showers. The controls for the seasonal weather pattern, and the deviations thereof, are given by the relative strength and position of the Tibetan High, the Sub-Tropical Jet-stream (STJ) and the monsoon trough over northern India. Occasionally large amounts of precipitation are provided by westerly disturbances (Reiter and Heuberger, 1960; Yasunari, 1976).

The surprisingly low annual precipitation values for the Gorakshep and Lhajung stations (about 400-500 mm) accord well with the generally small size, low surface velocity and thick debris cover of most glaciers in the area. There are, however, additional elements strongly influencing precipitation distribution. A growing body of evidence (Mùller, unpublished data from snow profiles in the Western Cwm; Hagen, 1961 ; Miller et al, 1965; Lanchow Institute of Glaciology, Cryopedology and Desert Research, 1975; Academia Sinica, 1975; Ageta, 1976; Yasunari and Inoue, 1978) shows that precipitation in the eastern Nepalese Himalayas increases drastically at the 5000-7000 m level on many peaks and ridges, particularly on south-facing slopes, whilst the bottoms of the main valleys are increasingly drier with higher latitude and altitude. This augmented precipitation seems to be especially marked at the height of the numerous mountain glaciers. This situation can be explained by orographic convection and local diurnal circulation, set in motion by strong radiative heating during the daytime of the slopes above the upper surface of the monsoon air mass, which is usually located at about 5000 m in the mountain valleys in the morning. During the course of the day Cu and Cb clouds extend readily up to the 7000 m level, bringing moist monsoon air to the glaciers, where local cooling induces precipitation.

The role of temperature The very sparse air temperature data available for the area (Table 3) also seem to be in general agreement with the ELA pattern. The mean annual air temperature quoted by the Lanchow Institute of Glaciology, Cryopedology and Desert Research (1975) for the period 1950-1960 for the Rongbuk Lamasery (5030 m), being approximately the same as that of the much lower station at Lhajung (4420 m), indicates a warmer climate than expected to the north of Mt Everest. When comparing the mean monsoonal air temperature of Gorakshep (5245 m) with that of Lhajung (4420 m), again a hardly permissible comparison, the former station appears relatively warm.

The environmental temperature lapse rate for the area was established in 1956 through 34 simultaneous measurements of values at 12 different sites in the Khumbu valley, ranging from 3950 m (Pangboche) to 8000 m (South Col) in elevation. The pre-monsoon lapse rate, based on 21 observations during May 1956, was found to be 0.71°C/100 m, i.e. fairly dry adiabatic, while the monsoon lapse rate (13 measure­ments in September and early October 1956) was found to be 0.52°C/100 m, i.e. strongly wet adiabatic. The mean value for the entire observation period was calculated as 0.63°C/100 m. The data also show that, due to the great irregularities

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in the release and consumption of latent heat during the locally varying condensation, precipitation and evaporation events, large variations in the environmental lapse rate must be expected for different times and locations. An overall value of 0.60°C/100 m seems appropriate for the Mt Everest region.

THE LATE PLEISTOCENE ELA

Methods Péwé and Reger (1972, pp. 193-195) discussed the merits of various methods in use to assess the position of the snow line, i.e. the ELA, in Wisconsin times. One approach is based on the positions of cirques (Flint, 1957), another attempts to reconstruct the former glacier surfaces (Porter, 1970) and a third method tries to find the past 'glaciation limit', as Ostrem (1966) did for the present. Péwé and Reger (1972) used only 'sharp, empty north-facing cirques' to establish the Wisconsin snow line in Alaska.

For the present study it was decided to apply the method which equates the ELA with the altitude of the junction of the cirque floor and the back wall. The back walls of many cirques in the Mt Everest area are very steep, often overhanging, permitting the establishment of a clear value. As there is little difference in the mean elevation of cirques of differing orientation, it seemed advisable to consider all cirques in the area.

Old moraines and cirques in the Mt Everest region (Fig. 3) On the basis of fieldwork carried out in 1956, a map was compiled of the Holocene and late Pleistocene moraines and the numerous empty cirques in the Imja Khola basin, above the Phortse-Tengpoche cross section. This map, part of which is shown in Fig. 3, contains evidence for four major stages in the glaciation of the upper Khumbu region:

(a) A Recent Stage, with several sub-stages, is represented by a sequence of fresh looking moraines produced since the little Ice Age. The oldest and best developed of these moraines rests against the inside of, and in a few places spills over, a very large moraine of the next (older) series. Iwata (1976) labels these moraines as part of his Lobuche Stage series; Fushimi (1978) includes them as the youngest members of his Thuklha Stage sequence Ti to T6.

(b) The lichen and vegetation covered, well consolidated moraines of the Dughla (Thuklha) Stage, with two and in places three main sub-stages, surround those of the Recent Stage, forming the most impressive and, through size and shape, the most striking ramparts which bulge out of the side valleys, partitioning the main valleys. 14 C dating of organic material from the Gorakshep area and lichenometric measurements (Millier, unpublished report) indicate that the Dughla Stage moraines belong to the little Ice Age.

(c) A well developed prehistoric moraine series, in appearance resembling and in age likely to correspond to those of the Egesen and Daun Stages in the Alps, is found several kilometres downstream from the Dughla moraines, again forming conspicuous features in the landscape. This moraine series was labelled Pheriche Stage (Mûller, 1958/1959 and unpublished report). Huge 'Eckfluren' at the confluence of former main glaciers belong to this period. The empty cirques must have been developed during and prior to the Pheriche Stage.

(d) Isolated remnants of moraines and glacial terraces witness to even older and more extensive glacier stands in the Khumbu Himal. Whether there are several, or only two such older stages, Ghat (U2) and Luklha (L1! ) as suggested by Fushimi (1978), needs further clarification in the field. The Thyangboche Stage proposed by Iwata (1976) is questioned by Fushimi (1978, p. 75, Table 2) and the present author. The

Equlibrium line altitudes in the Mt Everest region 87

glacial origin of the remnants reported by Heuberger (1956) at an elevation of only 2100 m near Tschjaubas in the pre-Himalayas is doubtful.

Chinese scientists (Lanchow Institute of Glaciology, Cryopedology and Desert Research, 1975, Table 3) compared the length of the late Pleistocene glaciers on the northern slopes of the central section of the Himalayas with the present length and found ratios of only 1.6 to 2.2, while typical glaciers of other Asian mountain chains were 3 to 6 times longer in the late Pleistocene than now. During the same time span the major glaciers of the Alps reduced much more in length. Fushimi (1978, Table 2) claims that in the main valley south of Mt Everest the areas of the largest glaciers in the late Pleistocene (Luklha Stage) were only 4 to 6 times greater than the present ones.

Thus the notion of a comparatively small-scale glaciation during the late, or probably the entire Pleistocene and Holocene times, for the central Himalayas, as suggested by Millier (1958/1959 and 1970), is gaining general support.

Comparison of recent and late Pleistocene ELA In Fig. 4 the recent and the late Pleistocene ELAs are compared in a SSW-NNE cross section which concentrates the three-dimensional ELA map information of Figs. 2 and 3 on a simple distance-altitude grid. The point of origin is Phunkhi, a small hamlet at the outlet of the Imja basin, below the Tengpoche (Thyangboche) monastery. The profile crosses the main mountain range at the foot of the west ridge of Mt Everest, at kilometre 30. The Unes of best fit for the two sets of points were drawn graphically; a linear representation did not seem justified.

The depression of the ELA in the Imja drainage basin is about 3 times as large ('vôOO m) at the southern end as at the main chain of the Mt Everest range, where it amounts to about 200 m. The calculated mean value for the ELA depression in the Imja basin was found to be 330 m (Table 2); the standard deviation is large.

The Lanchow Institute of Glaciology, Cryopedology and Desert Research (1975, p. 121) reports that at a distance of 30 km north of Mt Everest the late Pleistocene snow line is 200-300 m lower than that of today, and 50 km to the north it is about 500 m lower.

Discussion and interpretation of the late Pleistocene ELA depression The late Pleistocene ELA depression for the Mt Everest area seems somewhat smaller than that for most other parts of the world. For the Austrian and Swiss Alps, Gross etal. (1977, p. 244) report an ELA depression of about 430-450 m for the moist-maritime north slope and 310-340 m for the dry-continental interior during the Egesen Stage; for the Daun and Gschnitz Stages approximate overall ELA depressions of 400-550 m and at least 700-800 m respectively are given. Péwé and Reger (1972, p. 187) quote for Alaska a general depression of the Wisconsin snow line compared with today's of about 300-400 m in the west and 450-600 m in the east. In partial contrast to the Himalayan situation the vertical separation of the two surfaces becomes greater towards the drier interior. Hastenrath (1967 and 1971) reports, for the glaciers of the South American Andes, a decrease of the Pleistocene snow line depression from latitude 30°S (1500 m) to latitude 12°S (700 m) and also from the Pacific to the Atlantic side of the mountain chain.

Tectonic uplift It is tempting to explain both the general smallness of the amount of the ELA depression and its decrease from south to north and then slight increase, as the result of tectonic uplifting of the main crest of the Himalayas during this time span. Already Wager (1937) in his study of the Arun River drainage pattern detected a strong and

88 F. Mûller

MORAINES AND CIRQUE LOCAT

M O U N T E V E R E S T REGION

>sMM<mâ^ J\^-'J- XT'- (

Equilibrium iine altitudes in the Mt Everest region 89

Legend to MORAINES AND CIRQUE LOCATIONS'

J"7 | ^ j Moraine of Dughla Stage" ]Q v .J Snow- land Boundary

* * " * ^ Substage or indistinct part of above l i l i ^ - l Glacier (debris covered)

••*"**:. Moraine of Pheriche Stage" and older Glacier (exposed)

| C ^ - - / j Recent moraine / ^ | Empty cirques wi th altitude

r ^ f S S ï-ake t W i * 1 Eckf lur and/or terrace of I—j—-) "Periche Stage" and older

^> River or stream

Topography based on : 'Chomolungma Mount Everest" 1 : 2 5 OOO by E- Schneider

Khumbu H i m a I (Nepal)" 1 : 5 0 OOO by E. Schneider

FIGURE 3. Moraines and cirques in the ïmja basin.

90 F. Mûller

H < o

( i s e u i ) sanbjiQ pue aut-| uimjq;|;nb3 jo uo;ieAaia

9 a a

Equilibrium line altitudes in the Mt Everest region 91

continuing rise. On the basis of his broad experience in Himalayan tectonics, Gansser (personal communication) considers an uplift rate of up to 1 cm per year during the last 20 000 years as a reasonable assumption. A correction of some 200 m would make the ELA depression in the central Himalayas comparable to that elsewhere. However, lack of field data on the uplift rate makes it difficult to utilize this interesting hypothesis quantitatively.

Precipitation aspects The similarity of the shape of the ELA curves indicates that the same climatic elements were dominant during the late Pleistocene glaciation of the Mt Everest region as today. Precipitation played a major role, characterized by monsoons, westerlies and irregularities induced by high mountain topography, convection and the cooling effect of snow and ice surfaces.

The generally increased temperature gradient from low to high latitudes during the ice ages may have caused an increase of the precipitation gradient on the slopes of a major mountain range such as the Himalayas. This could explain the exceptionally strong steepening of the southern portion of the late Pleistocene ELA curve in Fig. 4 , however, it must be admitted that differences in the tectonic uplift rate could have the same effect. It seems that the decrease of precipitation northwards was slightly stronger in late Pleistocene times than today. Even if the height of the main mountain crest was lower by 200 m (or possibly 500 m at the time of the maximum glaciation) the monsoonal transgression to the north of the range was still limited and occasional, as today, and not general.

Late Pleistocene temperature depression The temperature difference between the late Pleistocene and the present must be larger than indicated by Fig. 4. Applying a lapse rate of 0.6°C/100 m for the altitude difference of the two curves yields a temperature depression of only about 1°C at the northern end of the profile and 3°C in the southern section. To this amount about 1-2°C must be added to account for the estimated 200-300 m uplift of the cirques. This then would give a temperature depression at the northern end of 2-3°C and in the southern portion of 4-5°C.

CONCLUSION

In spite of uncertainties about the accuracy of both the present ELA data and the 'cirque floor technique' of establishing past ELA values, much knowledge has been gained regarding the main characteristics of the present and the late Pleistocene glaciation of the area. Both are judged to be relatively small. Precipitation and temperature patterns have changed little compared to many other parts of the world. In a tectonically more stable area clearer results could be expected from such an investigation. There the glacier inventory would prove even more useful for the reconstruction of the palaeoclimate.

REFERENCES

Academia Simca. (1915) Mt Everest Region Scientific Research Report 1966-1968; Physiography of the Contemporary Glaciers (in Chinese): Science Publishing House, Peking.

Ageta, Y. (1976) Characteristics of precipitation during monsoon season in Khumbu Himal. Seppyo 38, special issue, 84-88.

Andrews, J. T. and Miller, G. H. (1972) Quaternary history of northern Cumberland Peninsula, Baffin Island, NWT, Canada. Part IV: maps of the present glaciation limits and lowest equilibrium line altitude for north and south Baffin Island. Arct. Alp. Res. 4, no. 1, 45-59.

Dhar, O. N. and Narayanan, J. (1965) A study of precipitation in the neighbourhood of Mt Everest. Indian J. Geophys. 16, no. 2, 229-240.

92 F. Mùller

Flint, R. F. (1957) Glacial and Pleistocene Geology: John Wiley and Sons, New York, USA. Fujii, Y. and Higuchi, K. (1977) Statistical analyses of the forms of the glaciers in the Khumbu

Himal. Seppyo 39, special issue, 7-14. Fushimi, H. (1978) Glaciations in the Khumbu Himal (2). Seppyo 40, special issue, 71-77. Gross, G., Kerschner H. and Patzelt, G. (1977) Methodische Untersuchungen fiber die Schnee-

grenze in alpinen Gletschergebieten. Z. Gletscherk. Glazialgeol. 12, no. 2, 223-251. Grosswald, M. G. and Kotlyakov, V. M. (1969) Present-day glaciers in the USSR and some data

on their mass balance. / . Glaciol. 8, no. 52, 23-50. Hagen, T. (1961) Nepal, p. 42: Kiimmerly and Frey, Geographical Publishers, Berne, Switzerland. Hastenrath, S. L. (1967) Observations on the snow line in the Peruvian Andes. J. Glaciol. 6,

no. 46, 541-550. Hastenrath, S. L. (1971) On the Pleistocene snow line depression in the arid regions of the South

American Andes./. Glaciol. 10, no. 59, 255-267. Hess, H. (1904) Die Gletscher, pp. 67-70: Friedrich Vieweg und Sohn, Braunschweig, Germany. Heuberger, H. (1956) Beobachtungen fiber die heutige und eiszeitliche Vergletscherung in Ost-Nepal.

Z. Gletscherk. Glazialgeol. 3, 349-364. Higuchi, K. (editor) (1976) Glaciers and climates of Nepal Himalayas. Seppyo 38, special issue,

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lozawa, T. (1978) Preliminary report on glacier inventory in the Dudh Kosi region. Seppyo 40, special issue, 78-84.

Higuchi, K., Fushimi, H., Ohata, T., Takenaka, S., Iwata, S., Yokoyama, K., Higuchi, H., Nagoshi, A. and lozawa T. (1980) Glacier Inventory in the Dudh Kosi region, East Nepal. In World Glacier Inventory (Proceedings of the Riederalp Workshop, September 197 8), pp. 95-103: IAHSPubl.no. 126.

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Humboldt, A. von (1844) Central-Asien. Untersuchungen uoer die Gebirgsketten und die vergleichende Klimatologie (translated from French by W. Mahlmann), vol. 2, pp. 155 and 203: Karl J.Klemann, Berlin, Germany.

Iwata, S. (1976) Late Pleistocene and Holocene moraines in the Sagarmatha (Everest) region, Khumbu Himal. Seppyo 38, special issue, 109-114.

Kurowski, L. (1891) Die Hone der Schneegrenze mit besonderer Berucksichtigung der Finsteraarhorn-Gruppe. Pe«c£',s Geogr. Abh. 5, no. 1,119-160.

Lanchow Institute of Glaciology, Cryopedology and Desert Research (1975) Basic features of the glaciers of the Mt Jolmo Lungma region, southern part of the Tibet Autonomous Region, China. Scientia Sinica 18, no. 1, 106-130.

Lichtenecker, N. (1938) Die gegenwârtige und die eiszeitliche Schneegrenze in den Ostalpen. In Verhandlungen der III Internationalen Quarter -Konferenz, Vienna, September 1936 (edited by G. Gôtzinger), pp. 141-147: INQUA, Vienna, Austria.

Meier, M. F. and Post, A. S. (1962) Recent variations in mass net budgets of glaciers in western North America. In Variations of the Regime of Existing Glaciers (Proceedings of the Symposium of Obergurgel, September 1962) pp. 63-77: IAHS Publ. no. 58.

Messerli, B. (1967) Die eiszeitliche und gegenwârtige Vergletscherung im Mittelmeerraum. Geogr. Helv. 22, no. 3, 105-228.

Miller, G. H., Bradley, R. S. and Andrews, J. T. (1975) The glaciation level and lowest equilibrium line altitude in the high Canadian Arctic: maps and climatic interpretation. Arct. Alp. Res. 7, no. 2,155-168.

Miller, M. M., Leventhal, J. S. and Libby, W. F. (1965) Tritium in Mt Everest ice — annual glacier accumulation and climatology of great equatorial altitudes. /. Geophys. Res. 70, no. 16, 3885-3888.

Mfiller, F. (1958/1959) Eight months of glacier and soil research in the Everest region. In The Mountain World (Swiss Foundation for Alpine Research), pp. 191-208: George Allen and Un win Ltd, London.

Mfiller, F.(1970) Inventory of glaciers in the Mount Everest region. In Perennial Ice and Snow Masses, pp. 47-59: UNESCO Technical Papers in Hydrology no. 1; also IAHS edition.

Mfiller, F., Caflisch, T. and Mfiller, G. (1976) Firn und Eis der Schweizer Alpen. Gletscherinventar. Publ. no. 57, Geographical Institute, Swiss Federal Institute of Technology (ETH), Zurich.

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Equilibrium line altitudes in the Mt Everest region 93

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38, special issue, 84-88.

DISCUSSION

0strem: I would like to draw your attention to LiestcSFs work near the Hardangerj^kulen ice caps in southern Norway. He found about 2°C difference between the present day situation and the situation when what are called 'late glacial' moraines were formed.

Meier: The present equilibrium line altitude (ELA) on large valley glaciers is generally lower than the ELA on smaller cirque glaciers. Thus, when you compare modern glaciers with old ones, you should consider only glaciers of the same size and type.

Miiller I agree. However, as the present cirques in the Mt Everest area are linked to valley glaciers and less well developed mountain glaciers, it seemed advisable to include all the glaciers in the area for this study.

Meier: The actual accumulation area ratio (AAR) for a steady state balance varies over wide limits, depending on the intensity of accumulation and ablation rates in the different areas: debris-covered ice, calving termini etc. We have measured AARs in Alaska and other states which range from about 0.50 to 0.85. Specification of the median altitude, corresponding to an AAR of 0.5, tells you nothing about the mass balance. The median altitude may be a useful parameter for describing a glacier, but I believe that it has little climatic significance compared with the ELA.

94 F. Mùller

Millier You are quite right in ascribing great climatic importance to the ELA. However, there are very few glaciers for which long series of ELA or AAR data exist and we are proposing the median altitude as a neutral approximation to the steady state ELA because the median altitude can be applied to almost any glacier for which topographic maps exist. Naturally, the median altitude for any particular glacier will be higher or lower than the true steady state ELA and this discrepancy depends upon the shapes of the hypsographic curve and of the curve for specific balance versus altitude. On the secular time scale, these shapes will probably not change much so that secular variations of the median altitude should reflect the corresponding change in steady state ELA with an error of only a few decametres or less. The TTS strongly supports the extension of the present glaciological network to obtain more mass balance data from areas where there are presently few data. Such new data should be used to calculate correction factors which can be applied to the median altitudes of glaciers in different regions, or of different morphological types, to give better approximations to the steady state ELA.

Rabassa: Flint and Fidalgo, in 1964, estimated the depression of the Pleistocene snow line in the Bariloche region as equivalent to a 5.7°C lowering of annual mean temperature. This value is almost twice those you have mentioned for the Mt Everest region.

Weidick: Regarding the dating of glacial stages, the development of organic sediments takes a long time so that they will be essentially younger than the moraines in question.

Vohra: The Himalayas has been tectonically active through the Pleistocene which introduces a complexity in the glaciation stages. The relative intensity of glacierization as known from Europe is not strictly applicable. I agree with Miiller that the palaeoglaciation in the Himalayas was not as high as today in many sectors.

Corte: In the Central Andes we find only the three younger systems of the Pleistocene glaciation. The oldest one is not found due to the fact that the Andes were not high enough to form glaciers. This supports what Miiller and Vohra have said regarding the elevation of the Himalayas in regard to past and present snow Unes.