Introduction

The British Ruwenzori Expedition, 1952, was led by Professor W. Q. Kennedy, of Leeds University, and collaborated with a Belgian expedition which was visiting Ruwenzori at the same time. Its main object was geological. As glaciologist of the expedition I remained for six weeks in the high parts of the mountain massif, studying in particular the recent glaciation there. I examined the glaciers both on the Congo side (in company with Dr. J. de Heinzelin, of Brussels) and—in more detail—on the Uganda side, with the help of Mr. I. R. Menzies, of Luanshya, Northern Rhodesia.

For a short distance Ruwenzori is the natural boundary between Uganda and the Belgian Congo (Fig. 1, p. 471). The mountain chain is about 120 km. long, lying in a north-north-east to south-south-west direction, and 50 km. wide at the southern end where it reaches the Equator. It rises very steeply from the savannas and equatorial forests of the lowlands to purely alpine regions. The highest peak is Margherita, 5119 m. (Fig. 2, p. 468).

Fig. 1.

Equatorial East Africa. Ruwenzori, orientated NNE., forms, for a short distance, the boundary between Uganda and the Belgian Congo. The mountain chain is about 120 km. long and reaches the Equator at its southern end. The latest information gives’ the height of Margherita as 5119 m.

Fig. 2

Margherita (5119 m.), the highest peak of Ruwenzori. In the, foreground, the Stanley Plateau

Ruwenzori is built mainly of pre-Cambrian gneisses, migmatites, metamorphic shales and amphibolites with a complex geological history. (By contrast, the other two glacier-covered mountains in Africa—Kenya and Kilimanjaro—are both volcanoes.) Opinions differ as to when uplift began.Reference Johnson and McConnell ¹ Judging by the terraces and ledges in the valleys, it seems to have been intermittent, and is probably still proceeding.

Pleistocene Glaciation

The sharp sculpture in the peak regions of Ruwenzori and the profiles of many of its valleys are largely due to earlier glacierziations. The climate and vegetation make the finding and analysis of glacial deposits very difficult. At the foot of Ruwenzori great deposits of glaciofluvial material (containing boulders up to

m. in diameter) cover the bottoms of the valley mouths and can be followed out on to the savanna. These could not have been deposited under existing conditions and are evidently the work of earlier glacierizations. Natural sections (in cuttings and gulleys) revealed a horizon which may mark the boundary between deposits of different ages—perhaps even of different glacierizations—though our cursory observations do not justify any firm conclusions about this. Our examination of the terminal moraines, however, inclined us to the prevailing opinion that there is direct evidence of only one Pleistocene glaciation.Reference Nilsson ² It is possible that uplift (which has probably been continuous since the Cretaceous) created conditions favourable to the extension of the glaciers in the last Pleistocene glaciation.

Our present knowledge of Ruwenzori’s Quaternary geology only allows the plotting of very approximate boundaries of the Ice Age glaciation (Fig. 3, p. 471). This is supplemented by aerial photographs, on which a few formations are discernible; by the numerous glacially eroded “rock basin” lakes marked on the available maps; and by the level at which the Ice Age glaciers built up their terminal moraines (about 2000 m. above sea level on the Uganda side compared with 4400 m. above sea level where the present glaciers end). Boulders measuring more than

m. occur occasionally outside the outermost terminal moraine. Ice transport seems probable and it may be that they were carried there by an advance of too short duration to permit the formation of significant terminal moraines.

Fig. 3.

Map of the central area of Ruwenzori showing the present glaciers (dotted lines) and the approximate boundary of the maximum Ice Age glaciation. The Ice Age glaciers generally consisted of networks of ice streams, and the area within the boundary line was accordingly not all covered by ice

On the Congo side, no traces of moraines have been found below about 3800 m. above sea level, though most of the valleys at lower levels remain to be examined. The general impression, however, is that glacier cover was not as extensive as on the eastern flank of Ruwenzori.

The extant moraine walls show that the retreat of the glaciers was not uninterrupted. Recession from the outermost terminal moraines appears to have been slow at first, and was broken by two—or possibly three—halts resulting in the formation of moraines. Later it was more rapid, and the glaciers withdrew until, judging by their terminal moraines, they cannot have been much larger, and were probably even smaller, than at present (Fig. 4, p. 468). At some later date, the climate changed, the glaciers advanced and more moraines were formed. There are at least four, possibly five, Pleistocene terminal moraine belts, of which some at least include minor halts or re-advances.

Fig. 4

The melt area of the Stanley Glacier in 1932. In 1952 the front part of the glacier was hidden by the cliff in the foreground. Successive white lines indicate from the left: the last ontal moraine built Moraine; up by the Pleistocene glacier probably before this thawed completely; the Late-glacial the maximum post-glacial extension of the recent glacier tongue; the outermost but one of the recent terminal moraines; the position of the glacier front in about 1900

Photograph by the Belgian Ruwenzori Expedition 19326

The relative distances between the several moraine belts and their respective altitudes above the sea vary much in different parts of the mountain chain. One reason for this is the unequal accumulation areas from which the glacier tongues flow. The probable difference in the extent of glaciation on the eastern and western flanks of Ruwenzori could be due to the same cause. On the steep Congo side the topography does not favour the formation of any really large ice stream systems.

The Present Glaciers

The very steep slopes of the highest parts of Ruwenzori, and the altitude of the present glacierization limit there (about 4600 m.), thus preclude the possibility of any more comprehensive recent glacierization. (At lower levels the topographical conditions would be more favourable for glacier formation.) There are to-day some forty glaciers in the massif. All are small, and together hardly cover more than 10 km.². From the available maps, the present extent of ice-cover can only be roughly estimated.

There are glaciers on the six highest peak complexes: Mt. Stanley, 5119 m., Mt. Speke, 4914 m., Mt. Baker, 4873 m., Mt. Emin, 4802 m., Mt. Gessi, 4769 m., and Mt. Luigi di Savoia, 4665 m. (Fig. 3). The first two have the largest accumulation of ice and firn, in the form of relatively large ice caps which are the accumulation areas of steeply dropping glacier tongues (Fig. 5a and 5b, p. 468). The Ruwenzori glaciers are almost all either valley glaciers or transitional between valley and hanging glaciers.

Fig. 5a

Mt. Speke from the west

Fig. 5b

The eastern glacier tongues of the Stanley Plateau. Margherita in the background

Circumstances compelled us to restrict our investigations mainly to Mt. Stanley. Here there are about ten glaciers. The firn areas of seven of them are on or in contact with the Stanley Plateau, which lies immediately to the south of the highest peak, Margherita (Fig. 2). This relatively large firn area, the western part of which is nearly 4800 m. above sea level, slopes steeply to the east, and divides at about 4650 m. into three separate glacier tongues. The firn areas of the other outlet glaciers from the Stanley Plateau—the Elena, Mobius, South-West and West Stanley Glaciers—are not on the plateau and they may be regarded as isolated units. Of these, the West Stanley Glacier (on the Congo side) and the Elena Glacier (on the Uganda side) were studied for evidence of fluctuation.

Our main sources of information regarding the variations in size of the glaciers during their most recent history have been the records of expeditions since the Duke of the Abruzzi’s expedition of 1906 first succeeded in reaching the high parts of Ruwenzori.Reference Filippi ^3, Reference Humphreys ^4a, Reference Humphreys ^b, Reference Gnmne ⁵ These comprise somewhat general descriptions of the glaciers, accompanied by more or less diagrammatic maps, and photographs. The latter were particularly useful for our purpose.

Post-Glacial Fluctuations

The Economy of the Elena Glacier

As part of our study of the factors affecting the changes of volume of the glaciers, the material economy or “budget” of the Elena Glacier, on the eastern flank of Mt. Stanley, was computed, in conjunction with meteorological observations from 20 July to 14 August 1952 recorded below. It was found to be negative up to the beginning of August, and then positive until the end of the observation period. This may indicate that ablation was giving way to accumulation about the time our observations were made. In June and July ablation predominated, as indicated by a layer of dirt about 2 cm. thick on the glacier surface.

Several similar dirt layers were observed in crevasses (Fig. 9, p. 468). To make a more detailed examination of these, and of the firn in general, we dug four pits at different levels in the firn area. These showed that the firn was stratified; besides the dirt layers, which were alternately thick and thin, there were ice crusts and layers of firn of varying grain size (Fig. 10, p. 475). The sequence was practically the same in all the pits. The layers of dirt, coarse-grained firn and ice indicated melts, while the intermediate fine-grained firn was relatively unaffected by ablation.

Fig. 9

Crevasse with two well-marked dirt bands representing June-July ablation periods. The firn between them is one year’s accumulation surplus. Just below the upper dirt band is one less distinctly marked which represents the comparatively weak ablation period probably occurring in January and February

Fig. 10.

Firn profile in a pit in the Elena Glacier showing the specific gravities

A rain gauge at about 4000 m. above sea level has recorded low precipitation values in January and February (no information is available for December) and in June and July.Reference Osmaston ⁸ This is borne out by the records of permanent meteorological stations in the immediate vicinity of Ruwenzori. ⁹ The two maxima and two minima characterizing this periodicity readily fit the observed firn profiles on the Elena Glacier, the thick dirt layers being formed in June and July and the less marked layers in January and February and possibly also in December. It must be remembered that snowfalls have been recorded in the upper parts of Ruwenzori in every month of the year; melting probably also occurs every month. To speak of accumulation and ablation periods thus merely means that the budget is mainly positive in the one and negative in the other.

While our budget studies were too meagre for any general conclusions to be drawn, they possibly justify our pointing out some tendencies in the conditions governing ablation and accumulation.

In Fig. 11 (p. 475), Curve I is based on observations made by Mr. Menzies in December 1953. It clearly shows the accumulation increasing with altitude. In Fig. 12 (p. 475), Curve I (for the accumulation period 5–14 August 1952) shows no such increase with altitude, the precipitation being fairly evenly distributed. Though the period of observation is limited, the facts are consistent with the interpretation that the surplus accumulation tends to increase from 4450 m. up to 4650 m., and then to diminish at higher altitudes.

Fig. 11.

Economy of the Elena Glacier

• I. Accumulation surplus about August—early December 1953

• II. Accumulation surplus in budget year 1951–52 (August–August)

• III. Accumulation surplus in the first half of the budget year 1951–52

• IV. Accumulation surplus in the second half of the budget year 1951–52

Fig. 12

• Curve I. Accumulation surplus 5–14 August 1952

• Curve II. Ablation 1–5 August 1952

• Curve III. Ablation 22 July–5 August 1952

If we now consider the ablation curves in Fig. 12 (Curves II and III, covering the earlier part of our observation period) we find that ablation tends to diminish from the glacier tongue up to 4650 m., where it begins to increase. Thus ablation seems to be greatest at lower and at higher altitudes, which perhaps explains the decreasing surplus of accumulation above the 4650 m. level indicated by Curve I in Fig. 12. The view that ablation increases above 4650 m. is also supported by Curves II, III and IV in Fig. 11, showing accumulation surpluses for the budget year 1951–52. It should be remembered that normal ablation curves in higher latitudes show the ablation decreasing fairly rapidly with increasing altitude.Reference Ahlmann ¹⁰

We were unable to determine the relative values of meteorological factors and of radiation in ablation. However, with the possible exception of evaporation, the meteorological factors were obviously of small importance to the ablation, especially at higher altitudes, where everything pointed to radiation being the principal agent. This may explain the observed tendency for the ablation to increase above about 4650 m.

The run-off from the Ruwenzori glaciers is insignificant. Often we could only find small rills, and apparently very little melted firn and ice is drawn off. Most of it seems to freeze again, as we found re-frozen melt water both on the surface of and beneath the glaciers.

The time available in the field, and the physical difficulties of carrying out scientific study in such an environment, led to severe curtailment of the projected scope of our glaciological studies. It is hoped that enough has been accomplished to encourage further studies that will lead to closer long-distance correlation of climatic fluctuations.

A Note on the Meteorological Observations

Meteorological conditions on Ruwenzori are practically unrecorded except for a few rain gauges. The gauge at about 4000 m., mentioned above, records an annual precipitation of about 1700 mm.

The longest of our series of meteorological observations covers the period 20 July to 6 August 1952. The instruments were mounted at our camp, about 50 m. from the edge of the Elena Glacier, 4500 m. above sea level.

Temperatures were read on an Assmann psychrometer and on maximum and minimum thermometers. Observations were taken at 08.30, 14.30 and 20.30 hrs., local time. The mean diurnal temperature was calculated from the formula

Having no cage for our thermometers, they were suspended on a wooden cross 100 cm. above theground, and the maximum thermometer may therefore have been affected by direct solar radiation.

The warmest day of the period was 27 July, when the mean temperature was +0.1° C. The highest temperature reading was +9.7° C. on 3 August at 20.30 hrs., but that value is in all probability too high. The lowest temperature was −6.7° C. at 08.30 hrs. on 2 August (Fig. 13, p. 475). On one of the days between 8 and 12 August, however, the minimum thermometer registered −11° C.

Fig. 13.

Maximum, minimum and mean temperatures in the period 20 July–6 August 1952

Fig. 14

Above: Cloudiness in tenths in the period 20 July–6 August 1952, and Below: Relation of daily mean cloudiness to incoming radiation in the period 24 July–6 August 1952

The relative humidity varied from 71 per Cent to 98 per cent.

On most days the cloudiness was between nine- and ten-tenths (Fig. 14, p. 475, top). Clouds of stratus type were most common.

The barometer readings were practically constant throughout our stay in Ruwenzori. Their maximum amplitude was 5 mm. Hg.

Easterly winds predomInated, but in the evenings and at night a westerly catabatic wind was blowing. The wind strength never exceeded 5 m./sec., however, and its mean value for the whole period was 0.9 m./sec.

At this altitude the precipitation, aggregating 31 mm. H₂O in the period, was invariably in solid form. The precipitation-carrying clouds rose only exceptionally above 4300 m. However, 65 per cent of the observations had to be taken in dense fog. It may be mentioned that the snowfall from 7 to 14 August amounted to 32 mm. H₂O.

Clear weather seemed more frequent in the upper parts of the Stanley massif, above about 4700 m., than at our camp. Sometimes we could see relatively strong local winds radiating from the firn surface of the Stanley Plateau. These winds appeared to dissolve or hold back the masses of cloud rising from the valleys, thus improving the weather conditions on the Plateau.

Incoming radiation was astonishingly low, an average of 172 cal./cm.² per day being observed at our camp. The lowest value, 61 cal./cm.², was observed on 28 July. The maximum was 338 cal./cm.² per day. From Fig. 14 (bottom) it will be seen that the average cloudiness, in tenths, agrees well with the incoming radiation.