ASIA DURING THE GLACIAL PERIOD
The great area of Asia is at present but little explored for glacial
traces, but a certain amount of evidence has been collected, and the
data from the various mountain districts are consistent enough to map
out the general trend of the history of the continent during the Ice
Age.
The earth-movements which brought about the present configuration of
Asia were completed as regards their major details by the close of
the Tertiary period. These movements left a number of great basins
closed in on all sides by enormous mountain walls; at first all these
basins contained lakes, and the subsequent geographical history has
consisted largely in the gradual silting up of the lakes and the
development of more and more arid conditions. The fluctuations of the
Ice Age were superposed on this secular desiccation, but except in
northern Siberia the part played by glaciation in the history of the
country has been relatively small.
Consider for a moment the relief of Asia. The orographic centre may
be taken as the great Pamir plateau, the “Roof of the World,” with
an average elevation exceeding the height of Mont Blanc, diversified
by ranges of mountains exceeding 25,000 feet in places. East of this
is the great plateau of Tibet, 10,000 to 17,000 feet, bounded on the
south by the mighty Himalayas, and on the north by the mountains
of Kuen Lun. On the north the Pamir plateau is bounded by the Alai
range, passing north-east into the Tian-Shan mountains, rising to
24,000 feet in Khan-tengri. Still further north-east comes the Altai
range, with an elevation of 9000 feet. East of Lake Baikal lie a
series of ranges averaging 8000 feet in height, and passing into the
Stanovoi range of eastern Siberia and the mountains of Kamchatka.
The Himalayas, owing to their heavy snowfall derived from the
south-west monsoon, bear numerous great glaciers, but with the series
of ranges extending from the Pamirs to north-east Siberia the case is
different. These ranges all rise above the snow-line in places, but
owing to the scanty snowfall they bear at most a few small glaciers
on their northern sides, and none at all on the slopes which face
towards the deserts of western China, and in all cases the glaciation
is very slight in comparison with their elevation.
This distribution was characteristic also of the Ice Age. In the
Pamirs there is evidence of two periods when the glaciers had a
greater extent; in the first they extended to a level of 5000 feet,
in the second to 7000 feet. The present limit of the glaciers lies at
about 10,000 feet. The first glaciation was remote, for the moraines
are worn and weathered, but the second was much more recent, for
the moraines are fresh, and in some cases there are still masses
of “dead” ice buried beneath great accumulations of debris and
occasionally exposed by slips.
In the Tian-Shan mountains there are remains of two glaciations.
The earlier was the greater, and the glaciers descended well below
10,000 feet. This glaciation was followed by a long interval, when
the erosion of the rivers converted the U-shaped glacial valleys into
V-shaped gorges. A second glaciation descended to a level of 10,000
feet, and again developed U-valleys to this level; the end-moraines
of these glaciers are young and fresh-looking. In the Altai range
there were also two glacial periods. In the older and greater the
snow-line was depressed by 3000 feet. The glaciers attained a length
of twelve miles and descended to a level of only 3000 feet above the
sea. The second glaciation was less extensive.
So far we have been dealing with small mountain glaciers only. But
in north-eastern Siberia we find a different state of affairs. The
Stanovoi and Verkhoiansk mountains were heavily glaciated, and during
the first glaciation were probably the centre of an actual ice-sheet
similar to that of Scandinavia. The ice descended the valleys of
the rivers Yana, Indijirka and Kolyma and covered the New Siberian
Islands, which were at that time connected with the mainland. The
upper valley of the Lena was also heavily glaciated by an ice-sheet
moving southward, probably from the Patom highlands. When this
glaciation drew to a close the source of supply among the mountains
ceased, and the ice on the lowlands and in the lower parts of the
river valleys was left stranded as “dead” ice. When the mountains
became free of ice, the re-born rivers carried great quantities of
moraine-clay and other debris with them, and flooding the ice-surface
over wide areas deposited their load above the ice. In course of
time the remains of the ice-sheet were deeply covered by a layer of
earth and stones, which prevented the ice from melting and preserved
it to the present day. This is the probable origin of the well-known
“fossil ice” of Siberia. Other theories have been put forward, such
as the freezing of ground water during the winter, but none are
satisfactory, and that given here was generally adopted by Russian
geologists.
During the long warm interglacial which followed, the surface of the
thick earth-layer covering the ice bore low-growing herbage in the
same way as any other earth-surface. (A parallel to this is found
in Alaska, where the glaciers terminate among the forests, which
actually grow over the moraines covering their snouts.) The rivers
cut their way down through the earth and ice, exposing ice-cliffs,
which were quickly buried by talus from above. The mammoth and
woolly rhinoceros roamed the land, and their tusks remain in great
numbers as the “fossil ivory” of Siberia and the Arctic Ocean. Still
more remarkable is the fact that mammoths have been found buried
entire, and preserved by the frozen ground to the present day. It is
difficult to say how the animals reached such a position, but most
probably they sank into swamps formed during the summer and were
quickly frozen.
In western Europe the mammoth and woolly rhinoceros are regarded as
indications of severe climate, but their presence in north-eastern
Siberia in large numbers is evidence of a climate probably somewhat
warmer than that of the present day, especially as regards the length
of the vegetation period. Probably the winter snowfall also was less
than now. It is difficult to see how the fauna could have moved from,
say, the New Siberian islands into a warmer climate each winter, for
the winter climate becomes markedly more severe as one penetrates
south from the Arctic coast into the interior. It is possible that
the mammoth and woolly rhinoceros hibernated during the winter.
After this interglacial there came a recrudescence of glacial
conditions. In this case, however, the Stanovoi and Verkhoiansk
mountains and the Patom highlands were not buried in an ice-sheet,
but became the centre of great valley glaciers, which reproduced the
well-known glacial phenomena—corries, glacial terraces, U-valleys,
etc. The ice extended down the great river valleys, leaving a typical
moraine landscape on either side, and again reached the New Siberian
islands. In course of time the climate ameliorated, again commencing
in the south, and again the ice of the glaciers was buried. In the
New Siberian islands the happenings are summarized very expressively
by a rock-section described by Vollossovitsch. The bottom of the
section is formed by the older layer of “fossil ice.” Above this is
a sandy clay with remains of meadow vegetation and shrubs, followed
by a fine clay with remains of alder and white birch, and the bones
of mammoth and rhinoceros. Above this comes another layer of “fossil
ice,” followed by clay with the dwarf birch, Arctic willow, and bones
of musk ox, horse and later mammoth. After this the coastal regions
sank beneath the sea for a time and marine clays were formed in a
climate somewhat warmer than the present. When the land rose again
the conditions resembled those now prevailing.
Though not part of Asia, reference may be made here to the
glaciation of Spitzbergen, which runs strictly parallel with that of
northern Siberia. The first glaciation was of the “ice-sheet” type,
originating in the region north of Storfjiord, filling the whole
of that fiord and extending south of South Cape. Barentz Land and
Stans Foreland were at least partially ice-covered. The ice-floor of
Spitzbergen, which resembles that of Siberia, may have originated
during this glaciation. This was followed by subsidence to 230
feet below present level, and the ice retreated, giving place to
an “interglacial,” during which frost was very active and largely
obliterated the traces of the ice-sheet. This “interglacial” was
followed by a second extension of the ice, which affected the valleys
and fiords only, leaving the plateaux free. This again was followed
by subsidence and a warm period.
In southern Kamchatka there was a great development of ice, but
in the form of a network of glaciers rather than of an inland
ice-sheet. In the east the ice reached the sea, but on the west it
left a zone forty to sixty miles broad, and up to a thousand feet
high unglaciated, so that there was the same difference then as now
between the rainy east side and the drier west side of the peninsula.
The present snow-line in the centre of southern Kamchatka is about
5500 feet, and at the maximum of the glaciation it must have been
fully 3000 feet lower.
This glaciation was followed after an interval by a second, which was
confined to the mountains. The moraines of this glaciation are much
fresher than are those of the earlier one.
In Japan the mountains were only just high enough for glaciers to
develop in the north. The moraines are old and weathered, and their
meaning has been disputed; but recent work by Simotomai and Oseki
seems to have established their glacial origin. The depression of the
snow-line necessary to produce them—about 3000 feet—fits in very well
with that observed in adjoining parts of the continent. The phenomena
were confined to small hanging glaciers in the Hida mountains which
cut out corries and descended to a level of about 8000 feet, leaving
small morainic ridges. This glaciation was probably contemporaneous
with the earlier and greater glaciation of Siberia. To the succeeding
interglacial may be attributed the marine deposits found near Tokio
containing corals, at present living some distance further south. No
trace of any subsequent glaciation of Japan has yet been found.
J. S. Lee has recently called attention to the existence of a
glaciated area in northern China, the evidence for which consists of
moraines and striated slabs found in southern Chi-li, and a glaciated
valley with travelled boulders in the north of Shan-si. The glacial
deposits in Chi-li are closely associated with a layer of quartzite
pebbles which continues southward beneath the loess on the eastern
side of the Tai-hang range, and is attributed to either torrential
rain or the melting of glaciers. J. Geikie had long ago stated that
there once existed ice-masses all over northern China, and considered
that the ice came from the Himalayas. This origin is impossible, the
probable source of the ice being the Yablonoi mountains in southern
Mongolia.
In the Himalayas the glaciers formerly had a much greater extension.
The glaciers at present extend downwards to 11-13,000 feet, but old
moraines are found at 7000 feet, and near Dalhousie on the southern
slopes of the Dholadar range to 4740 feet.
On the northern side of the Himalayas there was a great development
of ice over Tibet, but there was not a real ice-sheet such as
occurred further north. Oldham records three separate periods of
glaciation in Kashmir, but it is not yet possible to discuss the
glacial history of the Himalayas in detail. The latter is likely to
prove complicated, since the range is still rising, and has probably
been doing so either continually or intermittently throughout the
Quaternary.
The great development of ice in Tibet, which is now semi-arid,
owing to interception of the rain-bearing winds by the Himalayan
range, suggests a considerable alteration in the present
meteorological conditions. The Tibetan snowfall was probably due to
the Mediterranean storms, which now give a small winter rainfall
in north-west India, and which during the Glacial period greatly
increased in strength and frequency and occurred throughout the year
(Chapters IV and VI), giving the Pluvial period of North Africa.
These storms would pass across Persia and continue to the north of
the Himalayas, probably breaking up over the Tibetan plateau.
It is evident that, taking northern Asia as a whole, there have
been two general glaciations, of which the first was the more
severe, separated by a long interglacial, during which, in Japan
at least, the climate became appreciably warmer than the present.
The first glaciation is related to elevation in the Arctic basin,
which closed Bering Strait and united the New Siberian islands to
the mainland. It was almost certainly contemporaneous with the first
glaciation (Gunz-Mindel) of Europe. The ice began as glaciers on the
mountains as in Scandinavia, but, owing to the scanty supply of snow,
developed more slowly and only reached the dignity of ice-sheets
in north-east Siberia. Then followed subsidence below the present
level, wider opening of the Bering Strait, warm ocean currents and
a long interglacial. After this there was again elevation and a
re-development of ice-sheets, but apparently once only, and not twice
as in Europe. This glaciation probably corresponded in point of time
more or less with the Rissian, for the post-glacial dry of central
Asia appears to have been of enormous period length.
There is one other phenomenon which must be considered in connexion
with the glacial history of Asia, and that is the loess. Loess has
already been referred to in connexion with the glaciation of Europe,
but in China its development is much greater. Richthofen, who first
studied this deposit attentively, and to whom we owe the æolian
theory of its origin, found that it was formerly deposited in China
over a much greater area than that over which it is accumulating
at present, and attributes this cessation of growth to the heavier
rainfall brought by the Glacial period, which enabled the rivers
to cut back their valleys and drain some of the mountain basins,
formerly enclosed. He considered that loess can accumulate more
rapidly in a closed basin, where occasional floods leave behind
them layers of bare sand and mud, easily dried to dust, than in a
well-drained river valley where floods are rare.
In western Asia outside the limits of glaciation we have further
evidence of at least one Pluvial period in the former far greater
extent of all the enclosed lakes, due partly to greater precipitation
and partly to decreased evaporation. The Caspian Sea and Aral Sea
were extended to several times their present size and united into a
single sheet of inland water. Lake Lop-Nor was greatly increased in
size, and many of the desert basins, at present dry, were the sites
of salt lakes. This is especially the case in central Persia, where
there were large salt or brackish lakes.
These Pluvial conditions have not yet been correlated with the
glaciations of Asia, but, by analogy with the conditions in America
discussed in the next chapter, there is little doubt that they were
contemporaneous with one at least of the glaciations, and probably
there were two main Pluvial periods coinciding with the two Glacial
periods. At Baku, on the shores of the Caspian river, Pumpelly has
found old shore lines at heights of 600, 500, and 300 feet above the
present level of the water. Still more interesting are the conditions
found by Sven Hedin in the Kavir basin of Persia. Here there are
lacustrine clays and silts referable to a Pluvial period covered by
beds of almost pure salt, suggesting a rapid and complete drying up
of the lake. Above this again are further silts indicating a return
of Pluvial conditions. In addition to this the succession of silts
and clays show that there were several minor fluctuations superposed
on the main wet periods, giving ten moist phases altogether.
BIBLIOGRAPHY
Many of the more important references are in Russian, and for these
reference is made to summaries in other languages.
Sevastianov, D. P. “On the glaciation of the extreme north-east of
Siberia.” _J. 12 Congr. Russ. Nat._, Moscow, 1910, No. 10, p. 491.
(Russian, see _Geol. Centralblatt_, 15, p. 205.)
Riesnitschanko, W. “Ancient and modern glaciers of the
south-western Altai.” _Mem. Russ. Geogr. Soc._, 48, 1912, p. 357.
(Russian, see _Geol. Centralblatt_, 19, p. 131.)
Komarov, W. “On the Quaternary glaciation of Kamchatka—Travels in
Kamchatka in 1908-9,” Vol. 1 (Russian, see _N. J. Min._, 1915, Pt.
2, P. 117).
Merzbacher, G. “Zur Eiszeitfrage in der nordwestlichen Mongolei.”
_Peterm. Mitt._, Gotha, 57, 1911, p. 18.
Prinz, Gyula. “Die Vergletscherung des nördlichen Teiles des
zentralen Tien-schan-Gebirges.” Wien, _Mitt. K. K. geogr.
Gesellsch_, 52, 1909, p. 10.
Obrutschev, W. A. “Geological map of Lena gold-bearing region.” St.
Petersburg, 1907. [Text in Russian; see _Geol. Centralblatt_, 12,
pp. 507-9.]
Simotomai, H. “Die diluviale Eiszeit in Japan.” Berlin, _Zs. Ges.
Erdkunde_, 1914, p. 56.
Oseki, K. “Some notes on the glacial phenomena in the North
Japanese Alps.” Edinburgh, _Scot. Geogr. Mag._, 31, 1915, p. 113.
Lee, J. S. “Note on traces of recent ice-action in North China.”
_Geol. Mag._, 59, 1922, p. 14.
Burrard, S. G., and Hayden, H. H. “A sketch of the geography and
geology of the Himalaya Mountains and Tibet.” Calcutta, 1907-8.
Hogböm, G. “Bidrag till Isfjordsomradets kvartargeologi.” _Geol.
Foren. Stockholm Forb._, 1911. (Spitsbergen; résumé in German.)
Richthofen, F. Freih. von. “China.” 5 Vols., 1907-12. (Loess, see
Vol. 1, p. 74 ff.)
Hedin, Sven. “Some physico-geographical indications of post-Pluvial
climatic changes in Persia.” _Internat. Geol. Congr._, Stockholm,
1911. “_Die Veränderung des Klimas._”