ON SOME OF THE PHENOMENA OF GLACIERS, WITH SPECIAL REGARD TO THOSE OF
NEW ZEALAND
_The cause of glaciers_—_Formation and
structure_—_Motion_—_Moraines_: _Lateral_, _medial_, _and
terminal_—_‘Surface’ moraines_—_Crevasses_—_Moulins_—_Glacier
cones_—_Glacier tables_—_Surface torrents_—_Avalanches_—_Cornices_
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[2] 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.’
[Footnote 2: _Handbuch der Gletscherkunde_, von Dr. Albert Heim, Zürich
(Stuttgart: Verlag von J. Engelhorn, 1885, 18 francs.)]
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 25_l._ 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.