PHOTOGRAMMETRIC STUDIES OF GLACIERS IN HIGH ASIA

R. FINSTERWALDER AND W. PILLEWIZER

An important part of the energies of various expeditions during the last ten years or so in the mountains of High Asia has been devoted to glaciology. The big glaciers of the Himalaya, Karakoram, and the Pamirs offered numerous problems, the investigation of which was only practicable during a few summer months— frequently a very brief period between the winter's end and the onset of the summer monsoon. It is not, therefore, to be wondered at that in those rugged mountain regions of High Asia photogrammetry has come to be applied in glaciological observations; for by means of this method field-work can be considerably reduced and the chief work be done at home.

Cartographical Surveys.

As a highly accurate map is the most important basis for all glaciological research, photogrammetry was first used successfully for survey. As long ago as 1909 already the Baltoro glacier in the Karakoram was surveyed by the method of intersection-photo- grammetry on the expedition of the Duke of the Abruzzi.

Stereo-photogrammetry was for the first time applied during the Pamir expedition of the Deutscher und Osterreichischer Alpen- verein in the year 1913, when the Borolmas and Kizilsu glaciers were surveyed, and subsequently the map was plotted by the Orel- Zeiss stereo-autograph.¹ On this occasion the great advantage of stereo-photogrammetry was proved. It was possible in a single short season in the field to do all the field-work necessary for a detailed topographical survey of the roughest country, with an accuracy unattainable by any other existing method of survey.

In the year 1921 Major Wheeler surveyed the massif of the Mount Everest by the method of intersection-photogrammetry. This photo-survey was an admirable piece of work, especially since a number of the photographs were taken at an altitude of more than 7,000 metres.

It may be mentioned here that during recent years, British officers have developed the intersection method of photogrammetry for surveys from the air; by means of oblique air-photographs, taken of the north-western face of Nanga Parbat, Captain D. R. Crone, of the Survey of India, compiled a map on the scale of i: 100,000, which proved of much value for the scientific and mountaineering work of the second German Nanga Parbat expedition, 1934.¹

 

The first time that terrestrial stereo-photogrammetry was employed in the Karakoram was in 1926, when Major K. Mason surveyed the upper Shaksgam valley with a Wild photo-theodolite. Among the glaciers shown on his map, the extremely pinnacled Kyagar glacier, which dams up the Shaksgam river, is of considerable interest. At the same time Mason succeeded then in contouring K⁶ at a distance of 42 miles by use of stereo-photogrammetry, a survey which could never have been carried out from so great a distance by any one of the older methods of terrestrial survey.²

The German-Russian Fedchenko-Pamir expedition in 1928 also devoted some time to special photogrammetric and glaciological work. Within the short time of two months 2,400 sq. km. were surveyed by ground stereo-photogrammetry in a rugged and difficult mountain region. On this occasion, the contoured map of the Fedchenko glacier, the longest glacier on earth outside sub-Polar regions, which was plotted with the stereo-autograph on the scale of 1 : 50,000, was of particular interest. The snouts of other glaciers were also surveyed on large scales and should serve as a basis for further investigations.⁷

In the year 1929 the surveys of the Baltoro glacier in the Karakoram were further extended by stereo-photogrammetry during the expedition made by the Duke of Spoleto.⁸

During the German Kangchenjunga expedition of 1931, K. Wien managed to survey the whole of the Zemu glacier in Sikkim by terrestrial stereo-photogrammetry, though he was hampered by extreme difficulties owing to bad weather and lack of triangulation control.⁹

 

In 1934, not merely a single glacier, but the entire region and surroundings of the Nanga Parbat group were accurately surveyed on the second German Nanga Parbat expedition. A contoured map of about 1,600 sq. km. in extent was accurately plotted on the scale of 1 : 50,000. This has proved invaluable as a foundation for glaciological research.¹

In the Shaksgam valley the photogrammetric surveys, started by K. Mason in the year 1926, were continued during the Shaksgam expedition of 1937 by M. Spender, who used an experimental Watts-Leica photo-theodolite designed at the Royal Geographical Society in London.²

The Two Types of Glaciers.

If we study carefully the above-mentioned glacier surveys, we can detect, according to their form of movement, two types of glaciers in High Asia.

With its well-marked and regular medial moraines, the Fedchenko glacier belongs to the type of large and slow-flowing glaciers which are to be found in all mountain groups of High Asia, especially in the Pamir and Karakoram districts.

Distinct from this type are those glaciers with a much greater slope, differing markedly in their movement. The Rakhiot glacier on Nanga Parbat belongs to the second type, forcing its ice downwards with the high velocity of 800 metres a year. The ice is not 'flowing' but tumbling in a Block-Schollen movement between the zones at the edges which show a high mobility. The entire ice- volume of the glacier moves downwards as a block between these lateral mobile zones, but the block is also broken up into Schollen, ice-clods from 1 o to 50 metres long, and varying in size, which show a movement of their own within the general block-movement of the glacier. The knowledge of this varied ice-movement is due to the possibility of measuring glacier velocity by photogrammetry, which was first applied to the photographs of the Fedchenko glacier in 1928.

The Photogrammetrical Measuring of the Ice-movement.

The method of measurement is as follows. On solid ground at the side of a glacier photographs are taken across the ice-current with a photo-theodolite; these are repeated from the same point at intervals of some days, so that the opposite side of the valley is included in all the photographs. Meanwhile, the ice-surface moves on, whilst the firm background of the valley-side remains stationary. The forward movement of stones or crevasses on the glacier's surface can then be measured with great accuracy by a stereo-comparator as parallaxes, p_x; the distances s between the points on the ice- surface and the firm bank are fixed stereo-photogrammetrically, and by use of the simple formula: d_s=px^.s /f the actual surface ice- movement d_s is obtained accurately within a few days; f in the formula is the focal length of the photo-theodolite.¹

A great advantage of this procedure is the small amount of field- work necessary to obtain the velocity of a glacier, for it can be carried out by one man within three hours. A matter of great importance in dealing with very broken glaciers is the fact that all the measuring work is carried out from the solid bank instead of on the crevassed surface of the glacier.

By measuring their velocities by photogrammetry, it was possible to investigate the flowing movement of the Fedchenko glacier and the very different Block-Schollen movement of the Rakhiot glacier. The latter is of particular interest, for there is little doubt that quite a number of the glaciers of the Himalaya and Karakoram move in the same way, as is shown by their extremely broken surfaces and by their numerous gaping crevasses and ice-pinnacles, which are the outward and visible signs of the Block-Schollen type, caused by steep slope and rapid movement.

The most rapidly moving glaciers of the earth, the Greenland glaciers, are all crevassed and probably moving in blocks. A similar character could be observed in the rapidly flowing glaciers of Spitsbergen,¹⁰ and all the advancing glaciers, the great velocity of which is a known fact, show rugged surfaces and signs of block-movement.

In those advancing glaciers it was observed that waves of great velocity run through their bodies far more rapidly than the normal rate of ice-flow of the glacier. This phenomenon is somewhat analogous to the high-water wave in rivers, the velocity of which exceeds by far the normal speed of the current. The rugged and broken surface of these advancing glaciers is a direct consequence of these rapidly moving waves, which no longer flow but 'break' in a tumbling downward movement.

A number of photographs which have been published in the Himalayan Journal show glaciers with extremely crevassed surfaces. Among them may be mentioned the Ghong Kumdan glacier which blocks the Shyok river.¹¹ The excessively rugged ice-dam of the Kyagar glacier in the Shaksgam valley which barred Major K. Mason's progress along this valley in 1926 is another.¹ Other examples of advancing glaciers with crevassed surfaces are to be seen in the papers of Ph. G. Visser in the ^eitschrift fiir Gletscherkunde.²

 

In connexion with these facts we may refer to the statements of J. B. Auden³ about the surface changes of the Nobande-Sobande glacier in the Karakoram. In the year 1929 this glacier showed a very smooth surface; in 1937 the surface had become extremely crevassed, a phenomenon which in our opinion may be due to a considerable increase of the glacier's velocity since the year 1929.

It seems, indeed, from the study of these photographs, that a number of Karakoram glaciers move in blocks with considerable velocity, while the Gletscher-(Jberschiebungen, mentioned by Ph. G. Visser in the Karakoram, also show signs of a Block-Schollen movement. This form of movement, which seems to be essential for rapidly moving glaciers, and which was for the first time observed at the Rakhiot glacier, requires further accurate investigations by the method of photogrammetry.⁴

The Determination of the Depth and the Economy of Glaciers.

Not only is it possible to deduce important facts regarding the mechanics of glacier movement by photogrammetry, but the knowledge of the velocity and the inclination of a glacier's surface obtained by this method enables one to draw conclusions regarding its depth by means of Lagally's formula, whose theory may serve as a working hypothesis.⁵

The Fedchenko glacier, which possesses a velocity of 170 metres per annum and an inclination of 4 per cent., was computed to be 550 metres thick in the middle part of its long ice-stream. This profile is yearly crossed by about 111 million cubic metres of ice. From these facts it is possible to estimate the amount of accumulation in the firn-regions of the Fedchenko glacier; if we calculate the summer-ablation we get an accumulation equivalent to a rainfall of i metre a year, an amount that explains the formation of large glaciers in the arid stone-desert of the Pamirs.¹

 

 

On the Rakhiot glacier, photogrammetrical measurements for movement took place in the year 1934. The calculations for depth led to the result that the uppermost profile is crossed by about 70 million cubic metres of ice a year, supplied by a firn-region whose area is no larger that 13 sq. km. If this volume of ice is compared with the volume flowing through the Fedchenko glacier, we see that there is only about 1J times as much in the latter, though the firn- region of the Fedchenko glacier is about 26 times as large as that of the Rakhiot glacier. The deduction is, therefore, that the latter receives a very much greater amount of accumulation, estimated as equivalent to from 6 to 8 metres of rainfall a year in the firn-region of Nanga Parbat.¹²

 

Similar calculations about the economy of the Zemu glacier have been made by photogrammetric measurements of movement. They prove that, with the aid of precise velocity measurements, it is possible to estimate the climatic conditions of glacier regions where the establishment and upkeep of meteorological stations would meet with unsurmountable difficulties.¹³ Systematic investigations of glaciers in High Asia, as have been initiated on the Nanga Parbat and the Fedchenko glaciers, should also lead to interesting revelations in meteorology and climatology, which might easily prove to be of great importance in these little-known regions.

Future Research on the Glaciers of High Asia.

In view of the success of these early glacier observations, how can we best employ the method of photogrammetry to get the most important results in High Asia? It seems to us that the work should be divided into two groups:

1. We should repeat and extend the systematic measurements of the Velocity of the glaciers of High Asia which have already been investigated in order to check former measurements and to provide new material for the study of a typical glacier's economy. For this purpose the Nanga Parbat glaciers would be the most suitable, more especially since further measurements on the Rakhiot glacier could considerably enlarge our knowledge of Block-Schollen movement. Repeat measurements of the velocity of the Zemu glacier would also be of great interest.
   In conjunction with these velocity measurements, repeat surveys of the glacier-snouts in these regions should also be made at the same time in order to establish any changes which may take place between each set of observations.
2. So far detailed photogrammetric investigations of glaciers have only been carried out on the Pamirs and in the Himalaya. It is of great importance that the study should be extended to the Kara- koram, which is not only a link between these mountain regions, but which also offers a number of most interesting glacier problems. Apart from its many great glaciers, among which may be counted several to be compared in length and type with the Fedchenko glacier, the Karakoram is certain to contain glaciers showing Block- Schollen movement, which may well be characteristic of many glaciers of our globe.

Finally, the phenomenon of advancing glaciers can be studied better in the Karakoram than anywhere else, since most of the glaciers of the earth have been receding for a long time, and do not offer this possibility.

A careful and detailed stereo-photogrammetric survey of a large Karakoram glacier with simultaneous systematic velocity measurements would give us the data we require to ascertain its economy. With this knowledge we can investigate the climatic conditions of the Karakoram, which are still very problematical, and compare them with the Pamirs and the Himalaya to the north and south.

Note by the Editor

Photogrammetric measurements of the tongue of a Karakoram glacier, such as the Chong Kumdan or Kichik Kumdan, during its advance, will also throw important light on the movement along sheer-planes parallel to the glacier-bed. The origin of this movement may well be connected with Block-Schollen movement, since it apparently does not occur on slow flowing glaciers of the Fedchenko type. It is easy to theorize, but, in fact, we require definite measurements and observations during the phenomenon of rapid advance in order to understand fully what actually happens (see 'The Study of Threatening Glaciers', and 'The Origin of the Rio Plomo Ice- Dam', in Geographical Journal, vol. lxxxv, 1935, pp. 24-49).

The interesting Minapin glacier in Nagar, the tongue and snout of which have now been studied for about 40 years, is another glacier which appears to exhibit Block-Schollen movement. An illustration of this glacier taken from the air is given in the 'Notes' section of this volume (see below, p. 184).

 

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