Paper read at a Meeting of the Society on 5 February 1949

Dr. Volkmar Vareschi, who came from Munich to work in the Geobotanical Institute (Geobotanische Forschungsinstitut Rübel) in Zürich, published from there in the years between 1935 and 1942 a series of articles upon his investigations of the pollen content of glacier ice, and especially upon their application to our knowledge of glacier structure and our theories of glacier movement. No other investigator appears to have entered this field of research, and it is entirely with Vareschi’s work and ideas that I am now concerned.

Not only snow, hail, and rain fall upon the great glacier fields, but also a great deal of dust, and with it a vast amount of pollen blown in from the surrounding plant-clothed countryside. Vareschi has shown how this pollen can be recovered, identified, and related to its sources. In particular he has demonstrated that as the composition of the pollen rain changes throughout the year with the successive flowering of various plant species, so in the thick annual increment of snow upon the upper firn, the annual procession can be recognized in the pollen types preserved.

Pollen grains are released from the sporangia of flowering plants and coniferous trees, and being small (between 10 and 100 microns in diameter) often travel great distances before settling to the ground. Although wind-pollinated plants, such as the majority of European trees, grasses and sedges, constitute the main source of air-borne pollen, considerable amounts also come from insect-pollinated species. When viewed beneath the microscope the grains are seen to have numerous characteristics of size, shape, pore-number and character, wall-thickness and sculpture, which permit identification to the degree of genus in most instances, and even to species in others. Thése facts of course lie behind the technique of pollen-analysis which has been so extensively applied to investigations of quaternary history, hay-fever, and the origin of honey.

Vareschi’s field method is to remove the surface ice and clean the face of a suitable crevasse, and after making notes of the stratigraphy of the ice, to cut out from 2 to 10 cubic dm. of uniform ice, melt it on a Primus stove and hand-centrifuge the melt-water, transporting the muddy residue to the laboratory in collecting vessels with some preservative such as thymol. In the laboratory the centrifugate is treated with strong hydrofluoric acid to remove mineral residue, and the remainder is mounted in glycerine on slides for examination. The counts can be made quantitatively, and amounts of pollen are found up to 5000 pollen grains per cubic dm. of ice. Together with the pollen there are also abundant organic remains of all kinds, but so far these have not been made the subject of analysis.

Vareschi made his first investigations on the firn of the Great Aletsch Glacier and compared the pollen content of the surface ice with the composition of the forests in the surrounding area of 2000 sq. km. A remarkable degree of correspondence was shown. He was also able to show that the spectral composition of the ice from different glaciers is characteristic if they are compared at equivalent seasons. In the Aletsch region the flowering times of species contributing to the pollen rain extend from March to August, with the hazel and alder early, pine and spruce succeeding in the summer, with the winter lime and Pinus cembra, the five-needled pine, as the latest.

On the Gepatsch Glacier of the western Ötztal Alps, Vareschi pursued his investigation of the relationship of this seasonal drift to ice layering. Samples were taken from three sites; the highest, at 3080 m., was in the centre of the firn; the middle, at 2780 m., was just above the ice-fall at the head of the glacier tongue; the lowest, at 2150 m., was in the tongue itself in the ablation region.

Samples taken from the highest site, where the ice was conspicuously banded, had a very different pollen content in the succeeding layers (Fig. 1 below). Some had a low pollen frequency and spring-flowering species only, others with high pollen frequency, summer-flowering trees and abundant grasses and flowering herbs, were clearly formed in mid-summer, whilst winter ice had almost no pollen in it. There was little relation between season of formation and the banding characters of ice grain size, colour and thickness. But certain bands of laminated dirty ice showed prodigious pollen frequencies without clear seasonal aspect (both early and late season pollen mixed together), and were evidently the result of melting of the ice formed throughout an entire season. It was possible by considering the results from a vertical series of samples to infer the progress of accumulation at the site through several years.

Fig. 1

Profile from the Gepatsch Glacier at 3080 m.

Col. 1 shows scale in metres

Col. 2 represents the characteristics of the ice layers recognizable in the crevasse face; the key is in Col. 5, the grain sizes, in centimetres, being approximate. The black dots show the positions from which samples for analysis were taken

Col 3. The arrows indicate the limits between the snow of successive years as indicated by the pollen analyses. The sample numbers are shown in heavy type

Col 4. The clock face diagrams show the pollen content, the heavy outline circle of which is proportional in area to the absolute tree pollen frequency. The proportions in which different types of pollen occur are indicated by the sizes of the various sectors, differently shaded (key in Col. 5). In general the early flowering species have a pale grade of shading; the latest flowering are darkest. Note the clarity of the distinction between the samples in the yearly aspects they severally represent. Spring and summer aspects preponderate

(See Zeit. Gletsch. Bd. 23, 1935, p. 271)

From the middle site similar results were obtained, although the mean annual thickness of ice seemed less than in the high firn.

At the lowest site, below the fracture zone, seasonal aspects and the annual layering were no longer recognizable.

It would seem from these results that whilst in the firn a type of movement prevails which preserves the horizontal aspect layering, in the glacier tongue this is replaced (or supplemented) by a smaller scale differential movement which effectively mixes the layers. Vareschi points out that one must beware of interpreting the results as if the results from the three sites represented a true time sequence. The layers formed in the high firn are thick and have the full seasonal range of aspect, but at lower sites these layers are buried and the accessible surface layers have formed in conditions of lower altitude leading to melting of summer layers, partial merging of aspects, or perhaps to fusion of the whole year’s snowfall.

In 1937 the investigations moved to the Clariden firn, where since 1926 Dr. Streiff-Becker had taken observations from a snow-gauge of the accretion and ablation on the firn. The site was at 2700 m., only 50 m. above the firn line, a circumstance strongly reflected in the history of the ice formation. The correspondence between the observed periods and depths of snow accretion was very close. A stained ice layer representing four years’ increment had the typical absence of seasonal aspect but very high pollen frequencies, thick layers of winter snow were recognizable by their very low pollen content, and in places the pollen showed the seasonal progression fully. At one level an ice-lens due to local melting in the autumn was seen to have a concentration of pollen as expected. Possibly of the greatest interest was the observation that the ice just below a heavy layer of concentration retained its low pollen content and clear seasonal aspect, thus showing that pollen grains do not percolate to lower levels through hair cracks in the ice, although fine mineral particles may do so.

Gratifying as these results are, it will be noted that there is no means in the pollen examination itself of saying how long any of the gaps should be taken to represent, and it is possible that the products of a period of melting may indeed be drained away altogether.

Vareschi’s latest and most important researches were made upon various systems of banding which appear in the tongue of the Great Aletsch Glacier, in particular what are locally called Ogiven. These are curved bands visible on the glacier surface, often in regular longitudinal series. They are best seen from a distance, and on the Great Aletsch, a glacier of moderate and even gradient, they have been often observed, photographed and recorded. They there fall into separate parallel series, each related to ice coming from a distinct ice field. The ogive itself is generally of darker block ice, whilst between one ogive and the next is paler and higher Buckel ice (see Fig. 2, p. 328 and Figs. 3 and 4, p. 333).

Fig. 2

Sketch-map of part of the Jungfrau component of the Great Aletsch Glacier, showing its ogive system and the results of pollen analyses made from surface ice samples taken at the indicated places. The convention for representation of the absolute tree pollen frequency, and the relative frequency of the different types, is the same as that in Fig. 1 where the key will be found. Samples taken between the dark ogive bands are typical winter ice with low pollen content. Samples from the ogive bands themselves have a high pollen content and spring, summer or autumn aspects. In certain instances within one ogive (e.g. samples 189, 190, and 190 a) the aspects follow the proper seasonal sequence; note the alder-pine dominance in the first, the spruce in the second, and the high spruce with Pinus cembra (with which lime is associated) in the third

(See Geob. Inst. Rübel, Vol 19, 1942, p. 91)

Fig. 3

Forbes’s Bands. Twin Glacier, Alaska

Fig. 4

Alaskan bands. Baird Glacier, Alaska

Photographs by Maynard M. Miller

Pollen investigation shows that the dark ogive ice has summer, spring and autumn aspects, whilst the paler intermediate regions have winter ice only. Moreover samples in sequence from the glacier snout upwards across a single ogive regularly show the correct seasonal sequence of aspects. It would therefore seem probable that the ogives are the original firn layers, more or less undisturbed since deposition, and here revealed by ablation. The curved form is regarded by Vareschi as due to curvature of the layers in conformity to the shape of the valley floor. If the ogives are in fact the transected layers of the firn, this fact should be clear from analysis of vertical profiles in the ogive region, and indeed full yearly cycles can be so demonstrated.

The ogive structure thus revealed was similarly shown to exist in the ogives of the Konkordiaplatz, and of the Gepatsch Glacier.

Between each of the parallel ogive systems in the Aletsch Glacier there is a belt of Pflugfurcheneis (Reid ridges or parallel bands) in which long tabular ridges of ice of varying height run parallel with the glacier axis. Pollen samples taken from along the length of any one band always show the same seasonal aspect, but series taken transversely across several bands, although disclosing many contrasting seasonal aspects, show no regular seasonal sequence, but only a fortuitous one. It is concluded that the movement here is quite different from that in the ogive region of the glacier tongue, and although more or less parallel with the seasonal bands, it is not concerned with differential moving of very small units (see Figs. 5 and 6, p. 333).

Fig. 5

Parallel banding of the ice and its covering of firn. Porno Glacier, Switzerland

Photograph by H. Hoek

Fig. 6

Parallel banding. Stein Limmi Glacier, Switzerland

Photograph by G. Seligman

In the glacier snout itself, and at the margins of the glacier next to the valley sides, there occurs a third type of ice, which upon examination proves to have no seasonal aspect differentiation at all. It seems that in this ice, which comes from the regions of greatest pressure, the scale of differential movement is finer than elsewhere.

Vareschi stresses that the pollen investigations show the character of the glacier movement rather than point directly to any particular mechanism of it. All the same he points out how in large degree his results conform to various parts of the hypotheses of Philipp and Finsterwalder. He considers that his findings agree with the views of Finsterwalder on the distortion of areas between the firn and the glacier tongue, and with Finsterwalder’s hypothesis of the course travelled in the vertical plane, according to which snow deposited highest on the firn comes out lowest on the glacier snout. It is indeed difficult to account for the regular seasonal structure of the ogives except upon a theory essentially of this character.

Whilst these results come from work which is as yet in an early and tentative stage, present features which are still unsatisfactory and are applicable to a limited number of glaciers only, nevertheless they have to be accepted as giving a systematic body of facts which will have to be taken into account in theories of glacier movement.

Certain criticisms and queries naturally present themselves. One wonders why samples have been always chosen from the centre of the recognizable ice layers, and whether there would not be great advantage in working with continuous samples throughout a profile, so as to reveal the full history of the deposit.

In the intermediate Gepatsch profile (as in other places also) there is a very remarkable lack of winter ice layers, and one wonders whether winter snow was ever present in this sequence. It would be remarkable indeed if the snow were consistently of spring and summer origin, but that is what the analyses suggest. If it is not so, then it is clearly of great importance to learn how the winter ice has disappeared, and whether winter ice can in fact vanish progressively with time and passage down the glacier leaving other layers intact.

One wonders how the presence of particles such as pollen grains, in very different frequencies in different layers, may affect the recrystallization of the ice, and indeed the development of minor slip-planes in the glacier —matters susceptible to both theoretical and experimental treatment.

Useful as the recognition of seasonal aspects has become, it has not hitherto been possible to recognize characteristic sequences in the profiles which might serve to date exposures of bands, and it is perhaps too much to hope for this. All the same, widespread disforestation or afforestation might give time indices recognizable in deeper glacier layers.

No working pollen analyst can fail to be impressed by the thought of the countless numbers of pollen grains from the melting glacier, swept down the rivers to the sea, or to incorporation in the archives of lake-bottom muds, and so Quaternary history finds itself also related to these glacier investigations.

It is much to be hoped that Vareschi will himself resume research in this field and that his work will also be checked and extended by new workers in fresh glacier regions where other conditions may well afford different opportunities.