Man and the Glacial Period 6

Man and the Glacial Period 6

In Sweden Dr. Svenonius estimates that there are, between latitudes 67°

and 68-1/2°, twenty distinct groups of glaciers, covering an area of four

hundred square kilometres (one hundred and forty-four square miles), and

he numbers upwards of one hundred distinct glaciers of small size.

 

As is to be expected, the large islands in the Polar Sea north of Europe

and Asia are, to a great extent, covered with _névé_-fields, and numerous

glaciers push out from them to the sea in all directions, discharging

their surplus ice as bergs, which float away and cumber the waters with

their presence in many distant places.

 

[Illustration: Fig. 8.--The Svartisen Glacier on the west coast of

Norway, just within the Arctic circle, at the head of a fiord ten miles

from the ocean. The foot of the Glacier is one mile wide, and a quarter

of a mile back from the water. Terminal moraine in front. (Photographed

by Dr. L. C. Warner.)]

 

The island of Spitzbergen, in latitude 76° to 81°, is favourably situated

for the production of glaciers, by reason both of its high northern

latitude, and of its relation to the Gulf Stream, which conveys around

to it an excessive amount of moisture, thus ensuring an exceptionally

large snow-fall over the island. The mountainous character of the island

also favours the concentration of the ice-movement into glaciers of vast

size and power. Still, even here, much of the land is free from snow and

ice in summer. But upon the northern portion of the island there is an

extensive table-land, upwards of two thousand feet above the sea, over

which the ice-field is continuous. Four great glaciers here descend to

tide-water in Magdalena Bay. The largest of these presents at the front a

wall of ice seven thousand feet across and three hundred feet high; but,

as the depth of the water is not great, few icebergs of large size break

off and float away from it.

 

Nova Zembla, though not in quite so high latitude, has a lower mean

temperature upon the coasts than Spitzbergen. Owing to the absence of

high lands and mountains, however, it is not covered with perpetual snow,

much less with glacial ice, but its level portions are "carpeted with

grasses and flowers," and sustain extensive forests of stunted trees.

 

Franz-Josef Land, to the north of Nova Zembla, both contains high

mountains and supports glaciers of great size. Mr. Payer conducted a

sledge party into this land in 1874, and reported that a precipitous wall

of glacial ice, "of more than a hundred feet in height, formed the usual

edge of the coast." But the motion of the ice is very slow, and the ice

coarse-grained in structure, and it bears a small amount only of morainic

material. So low is here the line of perpetual snow, that the smaller

islands "are covered with caps of ice, so that a cross-section would

exhibit a regular flat segment of ice." It is interesting to note, also,

that "many ice-streams, descending from the high _névé_ plateau, spread

themselves out over the mountain-slopes," and are not, as in the Alps,

confined to definite valleys.

 

Iceland seems to have been properly named, since a single one of the

snow-fields--that of Vatnajoküll, with an extreme elevation of only six

thousand feet--is estimated by Helland to cover one hundred and fifty

Norwegian square miles (about seven thousand English square miles), while

five other ice-fields (the Langjoküll, the Hofsjoküll, the Myrdalsjoküll,

the Drangajoküll, and the Glamujoküll) have a combined area of ninety-two

Norwegian or about four thousand five hundred English square miles. The

glaciers are supposed by Whitney to have been rapidly advancing for some

time past.

 

_In Asia._--Notwithstanding its lofty mountains and its great extent

of territory lying in high latitudes, glaciers are for two reasons

relatively infrequent: 1. The land in the more northern latitudes is low.

2. The dryness of the atmosphere in the interior of the continent is such

that it unduly limits the snow-fall. Long before they reach the central

plateau of Asia, the currents of air which sweep over the continent from

the Indian Ocean have parted with their burdens of moisture, having left

them in a snowy mantle upon the southern flanks of the Himalayas. As a

result, we have the extensive deserts of the interior, where, on account

of the clear atmosphere, there is not snow enough to resist continuously

the intense activity of the unobstructed rays of the sun.

 

In spite of their high latitude and considerable elevation above the

sea-level, glaciers are absent from the Ural Mountains, for the range is

too narrow to afford _névé_-fields of sufficient size to produce glaciers

of large extent.

 

The Caucasus Mountains present more favourable conditions, and for a

distance of one hundred and twenty miles near their central portion

have an average height of 12,000 feet, with individual peaks rising to

a height of 16,000 feet or more; but, owing to their low latitude, the

line of perpetual snow scarcely reaches down to the 11,000-foot level. So

great are the snow-fields, however, above this height that many glaciers

push their way down through the narrow mountain-gorges as far as the

6,000-foot level.

 

The Himalaya Mountains present many favourable conditions for the

development of glaciers of large size. The range is of great extent and

height, thus affording ample gathering-places for the snows, while the

relation of the mountains to the moisture-laden winds from the Indian

Ocean is such that they enjoy the first harvest of the clouds where

the interior of Asia gets only the gleanings. As is to be expected,

therefore, all the great rivers which course through the plains of

Hindustan have their rise in large glaciers far up towards the summits of

the northern mountains. The Indus and the Ganges are both glacial streams

in their origin, as are their larger tributary branches--the Basha, the

Shigar, and the Sutlej. Many of the glaciers in the higher levels of

the Himalaya Mountains where these streams rise have a length of from

twenty-five to forty miles, and some of them are as much as a mile and

a half in width and extend for a long distance, with an inclination as

small as one degree and a half or one hundred and thirty-eight feet to a

mile.

 

In the Mustagh range of the western Himalayas there are two adjoining

glaciers whose united length is sixty-five miles, and another not far

away which is twenty-one miles long and from one to two miles wide in its

upper portion. Its lower portion terminates at an altitude of 16,000 feet

above tide, where it is three miles wide and two hundred and fifty feet

thick.

 

_Oceanica._---Passing eastward to the islands of the Pacific Ocean, New

Zealand is the only one capable of supporting glaciers. Their existence

on this island seems the more remarkable because of its low latitude

(42° to 45°); but a grand range of mountains rises abruptly from the

water on the western coast of the southern island, culminating in Mount

Cook, 13,000 feet above the sea, and extending for a distance of about

one hundred miles. The extent and height of this chain, coupled with

the moisture of the winds, which sweep without obstruction over so

many leagues of the tropical Pacific, are specially favourable to the

production of ice-fields of great extent. Consequently we find glaciers

in abundance, some of which are not inferior in extent to the larger ones

of the Alps. The Tasman Glacier, described by Haas, is ten miles long

and nearly two miles broad at its termination, "the lower portion for a

distance of three miles being covered with morainic _detritus_." The

Mueller Glacier is about seven miles long and one mile broad in its lower

portion.

 

_South America._--In America, existing glaciers are chiefly confined to

three principal centres, namely, to the Andes, south of the equator; to

the Cordilleras, north of central California; and to Greenland.

 

In South America, however, the high mountains of Ecuador sustain a few

glaciers above the twelve-thousand-foot level. The largest of these are

upon the eastern slope of the mountains, giving rise to some of the

branches of the Amazon--indeed, on the flanks of Cotopaxi, Chimborazo,

and Illinissa there are some glaciers in close proximity to the equator

which are fairly comparable in size to those of the Alps.

 

In Chili, at about latitude 35°, glaciers begin to appear at lower

levels, descending beyond the six-thousand-foot line, while south of this

both the increasing moisture of the winds and the decreasing average

temperature favour the increase of ice-fields and glaciers. Consequently,

as Darwin long ago observed, the line of perpetual snow here descends to

an increasingly lower level, and glaciers extend down farther and farther

towards the sea, until, in Tierra del Fuego, at about latitude 45°, they

begin to discharge their frozen contents directly into the tidal inlets.

Darwin's party surveyed a glacier entering the Gulf of Penas in latitude

46° 50', which was fifteen miles long, and, in one part, seven broad. At

Eyre's Sound, also, in about latitude 48°, they found immense glaciers

coming clown to the sea and discharging icebergs of great size, one of

which, as they encountered it floating outwards, was estimated to be "_at

least_ one hundred and sixty-eight feet in total height."

 

In Tierra del Fuego, where the mountains are only from three thousand

to four thousand feet in height and in latitude less than 55°, Darwin

reports that "every valley is filled with streams of ice descending to

the sea-coast," and that the inlets penetrated by his party presented

miniature likenesses of the polar sea.

 

[Illustration: Fig. 9.--Floating berg, showing the proportions above and

under the water. About seven feet under water to one above.]

 

_Antarctic Continent._--Of the so-called Antarctic Continent little is

known; but icebergs of great size are frequently encountered up to 58°

south latitude, in the direction of Cape Horn, and as far as latitude

33° in the direction of Cape of Good Hope. Nearly all that is known

about this continent was discovered by Sir J. C. Ross during the period

extending from 1839 to 1843, when, between the parallels of 70° and 78°

south latitude, he encountered in his explorations a precipitous mountain

coast, rising from seven thousand to ten thousand feet above tide.

Through the valleys intervening between the mountain-ranges huge glaciers

descended, and "projected in many places several miles into the sea and

terminated in lofty, perpendicular cliffs. In a few places the rocks

broke through their icy covering, by which alone we could be assured that

land formed the nucleus of this, to appearance, enormous iceberg."[AG]

 

[Footnote AG: Quoted by Whitney in Climatic Changes, p. 314.]

 

Again, speaking of the region in the vicinity of the lofty volcanoes

Terror and Erebus, between ten thousand and twelve thousand feet high,

the same navigator says:

 

"We perceived a low, white line extending from its extreme eastern

point, as far as the eye could discern, to the eastward. It presented

an extraordinary appearance, gradually increasing in height as we got

nearer to it, and proving at length to be a perpendicular cliff of ice,

between one hundred and fifty and two hundred feet above the level of

the sea, perfectly flat and level at the top, and without any fissures

or promontories on its even, seaward face. What was beyond it we could

not imagine; for, being much higher than our mast-head, we could not

see anything except the summit of a lofty range of mountains extending

to the southward as far as the seventy-ninth degree of latitude. These

mountains, being the southernmost land hitherto discovered, I felt

great satisfaction in naming after Sir Edward Parry.... Whether Parry

Mountains again take an easterly trending and form the base to which this

extraordinary mass of ice is attached, must be left for future navigators

to determine. If there be land to the southward it must be very remote,

or of much less elevation than any other part of the coast we have seen,

or it would have appeared above the barrier.