With axe and rope in the New Zealand Alps/Chapter X
CHAPTER X
ON SOME OF THE PHENOMENA OF GLACIERS, WITH SPECIAL
REGARD TO THOSE OF NEW ZEALAND
In a work of this nature it may not be out of place to briefly describe some of those interesting features and phenomena which accompany the world above the snow-line.
Here is a quotation from a recent review of Professor Heim's work[1] by a prominent member of the English Alpine Club:—
'Some thirty years ago a systematic résumé of all that was known up to that date about existing glaciers appeared in the work of Professor Albert Mousson, "Die Gletscher der Jetztzeit," since which, with perhaps the exception of Major Hüber's "Les Glaciers," no attempt has been made to collect into a focus the light which numerous able observers and theorists have subsequently thrown upon the question. The intricacy of the problem has, indeed, increased almost in proportion to our enlarged knowledge of its conditions; and in spite of the labours of a large and very distinguished body of investigators, not only do many important points remain matters of dispute, but the very materials for a complete solution are still wanting.'
CAUSE OF GLACIERS
The joint cause of glaciers is precipitation and cold. A low temperature alone can do nothing without moisture, and this fact quickly disposes of the popular notion that glaciers invariably exist in cold countries. Thibet, for instance, and also some parts of Arctic North America are destitute of ice streams, though eternal cold may be said to reign supreme in these parts.
Imagine for a moment the higher mountains clear of snow and ice, and then watch for the formation of a glacier. Snow falls and fills up all the valleys and gullies, avalanches descend from the higher parts, and a great accumulation gathers in all hollows. By constant repetition of snow-falls (always provided a greater quantity is deposited than can be melted by the sun's rays and by the natural warmth of the earth's crust) great pressure is put upon the lower portions by the superincumbent accumulation, and aided by the infiltration of water and refreezing (or 'regelation' as the correct term is), a large body of ice is formed which at once begins to move down the valleys containing it.
GLACIER ICE
Glacier ice is not like the solid blue ice on the surface of water, but consists of granules joined together by an intricate network of capillary water-filled fissures. In exposed sections and upon the surface of the ice can be observed a 'veined' or 'banded' structure—veins of a denser blue colour alternating with those of a lighter shade containing air bubbles.
The cause of this peculiar structure has been the subject of much theorising amongst investigators, but hitherto I believe the greatest authorities consider that the explanation of the phenomenon is yet wanting.
glacier motion
The motion of glaciers is yet another bone of contention, but it is generally admitted that the cause of it is to be found mainly in gravitation, and is also partially accounted for by the strange property of 'viscosity' in what appears to the casual observer to be nothing more or less than a rigid solid.
Recently observations for ascertaining the rate of progress of the Tasman, Murchison, Hooker, and Mueller Glaciers have been made by the New Zealand Government Survey Department. Some of the results were embodied in a paper by Mr. J.H. Baker, the Chief Surveyor of the Provincial District of Canterbury, and will appear in the 'Transactions of the Australasian Association for the Advancement of Science' for 1891. At the late meeting of that body a committee was appointed to further these investigations, and a sum of 25l. voted for the aid of the same.
Before long, therefore, there will be put before the scientific public reliable measurements of the motion of several of the largest and least-known glaciers in temperate regions.
moraines
There is a remarkable feature of the glaciers of this country which stamps them as unique in one respect—I refer to the very extensive moraines. I write feelingly of this, for my acquaintance with them has been a very close one, and they have impressed me very deeply—in more ways than one.
The large glaciers of which I have written in this work are completely moraine-covered over their lower parts.
'surface' moraines
Moraines may be divided into four sections: 'Lateral' moraines, fringing the sides of the glaciers, their outlying portions often being 'dead'—that is, at present unmoved by the action of the ice, and forming banks, as it were, for the ice stream to flow between; 'medial' moraines, which begin at the junction of two streams of ice and often continue for many miles to the terminal face; 'terminal' moraines, formed by the depositing of detritus at the melting point or end of the glacier; and, lastly, 'surface' moraines (so called by Professor Hutton of Christchurch, N.Z.), which are the combined accumulations of the first two divisions in the lower parts of the glacier.
It is these 'surface' moraines that are such a characteristic feature of the glaciers situate on the eastern side of the chain in New Zealand. Of those on the western side I am not able to speak with authority, never having visited them myself; but I understand that they do not carry such a large quantity of detritus as those of the eastern slopes.
This disparity remains to be accounted for and awaits an explanation. I have a theory of my own upon the subject, which, however, as yet I would not like to put too strongly forward.
On both sides of Mount Cook, on Mount De la Bêche (ten miles further along the chain), and on a peak just north of the Hochstetter Dome (ten miles still further north) I have observed enormous exposed sections of the rock strata, which in each case dip at a steep angle from east to west, presenting slab faces, not easily disturbed by the action of the frost, to the westward, but broken and fast denuding faces ('basset' faces, as they are geologically termed) to the eastward. I am hoping at some future time to further investigate this interesting subject.
As the western glaciers, however, must descend steeper valleys than the eastern, I make no doubt that their rate of progress will be eventually ascertained to be greater than that of the latter, and this would militate largely against an accumulation of moraine upon the ice.
the surface of a glacier
All sorts of queer notions as to what the surface of a glacier is like exist. Indeed I have often heard people inquire if it would be possible to skate upon it!
Let us for a moment imagine ourselves at the head of the great Tasman Glacier, 8,600 feet above sea-level. All around us is snow, either freshly fallen or merging into névé. We begin to walk down, and at first, upon the steeper slopes, cross a few large crevasses and bergschrunds by means of snow bridges; then, as the incline becomes less steep, we walk for six miles or so upon a smooth surface of névé, or perchance knee-deep in fresh snow, and scarcely a crevasse exists. At the beginning of the great turn we gradually leave the névé and find ourselves upon hard, white ice, and soon transverse crevasses appear; these are a little further on cut by longitudinal crevasses forming the surface into huge squares, not flat on the top, but hummocky. A perfect network of crevasses cuts up the whole of the surface, but those parts on the outside of the curve are infinitely more disturbed than those on the inside, owing to the tension put upon them by the faster rate at which they have to move. After rounding the turn the glacier again consolidates and few crevasses appear, only the surface is covered with old wounds—if I may coin such a term—from the rents which have occurred at the turn, and presents a very undulating appearance. The little gullies are formed into watercourses and intersect the glacier in all directions. On our right, now, is the medial moraine formed by detritus from Mount De la Bêche, brought down partly by the Tasman and partly by the Rudolf Glaciers, and it stands up 100 feet or so above the surface of the clear ice on either side of it, owing to the protection from the sun's rays afforded by it to the ice beneath, so preventing 'ablation' or waste going on so quickly. We follow down for another four or five miles, and then cross this moraine (which has in the meantime joined that on the northern side of the Hochstetter Glacier) on to the Hochstetter on our right.
surface torrents and moulins
We are now immediately below the great ice-fall, and the surface of the glacier presents an appearance not unlike the back of some enormous caterpillar wrinkled transversely by crevasses, which close up as we proceed downwards, and furrowed longitudinally by two large or main watercourses whose icy banks are in places 100 feet above their respective torrents. These two small rivers are fed from every direction by minor watercourses, and a mile or two further down discharge all their contents into crevasses and moulins, or water-shafts in the ice.
glacier tables and cones—the action of warmth
The locality of the glacier on which we now are is very interesting, for Nature's mills are here seen at work day by day. Glacier tables—blocks of rock perched upon pedestals of ice formed by the protection from the action of the sun's warmth—are of frequent occurrence. Glacier cones—heaps of sand and small fragments of rock raised by a similar agency (after having been washed to one spot by water)—are in places all around us. Then, strange and contradictory as it may seem, we see thousands of holes, each with a stone at the bottom and filled with the bluest of blue water, formed also in the first place by the rays of the sun warming the stone and causing it to sink in the ice. It is well-known in physics that water at 39° Fahr. is at its heaviest, and as soon as the warm stone—the dark colour of the stone having absorbed more heat than the surrounding ice—begins to sink the warmer water follows it, whilst that in the neighbouring temperature of 32° Fahr. rises to the surface and becomes in its turn re-warmed, and so on. This peculiar current often bores the holes in the ice to a depth of many feet, and is only checked by a preponderance of cold. It is the larger stones, therefore, which rise upon the ice, and the smaller ones which sink.
'SURFACE' AND 'TERMINAL' MORAINES
We walk on down the ice stream, and soon the moraines on either hand close in upon us and we find ourselves on a mere wedge of ice, at the point of which we step on to the 'surface' moraine. Here the swearing begins, and it lasts right on to the terminal face four or five miles below, for it is one continual repetition of walking on loose and tumbling rocks, up one hillock, along a ridge, jumping from
Rock to rock with many a shock,
down another hillock, now and then starting a whole avalanche of many-sided and sharp-edged stones down a treacherous slope of ice, which we take for a surface deeply covered and sound of footing.
Skate on the surface of a glacier?
'Not much!' (as the Colonials say).
AVALANCHES
Very strange notions also exist amongst the uninitiated as to the nature of avalanches. The popular idea of an avalanche is derived from heartrending accounts of great sweepings away and annihilation of whole villages, and few of the general run of people seem to realise that in Alpine work almost any little descending mass of rock, snow, or ice is dignified by the name of avalanche. Snow avalanches are most frequent after fresh falls of snow followed immediately by warm weather, and after a little experience amongst the mountains one soon learns to detect their customary tracks. Ice avalanches are mainly caused through the overhanging portion of ice at the terminals of secondary glaciers—that is, glaciers which break off before descending to the valley or to the parent glacier below. The tracks of ice avalanches are almost invariably unmistakable and are swept night and day without cessation, and very frequently at regular intervals.
Rock avalanches are more treacherous, and one never knows when to expect them from above; generally in the early morning the frost holds the stones above in an icy grip, but as the sun melts the ice in the chinks the hold is released and a stone will descend into the couloirs or ditches which scarp the mountain side. If one happens to be below then it is a case of sauve qui peut and a rush for the nearest protection, for there is no saying how many tons, or indeed how many hundreds of tons, of loose rocks or stone may start in a wild and dusty rattle down the hillside.
But some snow avalanches almost crawl down the couloirs, and make a strange and ever-continued hissing as they move. These are composed of heavy and sodden snow, and begin after the sun has been up for some hours, continuing until nightfall. These are not so dangerous on a gentle slope, and one can often waddle or half glissade down in the midst of one with perfect safety, though they make one uncomfortably wet.
cornices
Cornices are a frequent source of danger to the mountaineer. They are formed by the snow drifting over one edge of a ridge and forming a hanging mass. It is needless to say that one soon learns to walk some feet away from the outer edge of a cornice, for after poking one's axe-handle through three feet of snow, and peeping through a blue hole down a precipice of perhaps 1,000 feet or so, it is not difficult to fancy what the result would be should the cornice break.
- ↑ Handbuch der Gletscherkunde, von Dr. Albert Heim, Zürich (Stuttgart: Verlag von J. Engelhorn, 1885, 18 francs.)