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EOLIAN LANDSCAPES OF SIBERIA

Дата публикации: 08 сентября 2018
Автор(ы): Gennadiy Ufimtsev
Публикатор: Шамолдин Алексей Аркадьевич
Рубрика: RUSSIA (TOPICS)
Номер публикации: №1536411208


Gennadiy Ufimtsev, (c)

by Gennadiy Ufimtsev, Dr. Sc .(Geol. & Mineral.), Institute of the Earth Cmst, RAS Siberian Branch

Eolian, or wind-borne forms of relief are rather common in many regions of Siberia. They occur, for example, in the estuary of the Viluy (Yakutiya), and in the center of the Charskaya basin, or kettle, where there are real barchan dunes towering over a swampy plane overgrown with stunted vegetation and speckled with numerous thermokarstic lakes. In the Zabaikalye region, on the right bank of the Onon River, some of the old kossak villages are literally buried in sand, and one can see in the steppe above the valley big deflation basins with sand ridges further to the south-east.

Back in the 19th cent. the district center of Selenginsk was abandoned by its residents who could no longer endure the "ruinous" impact of the windsand. All you can see there now are ruins of an old church encircled with ridges of sand. On the south- eastern shores of Lake Baikal strong north-westerly winds form on the beaches big dunes, and "mantles" of golden sand cover their slopes. In the Tunkinskaya basin (South-Westem pribaikalye) there is a whole sand mountain, named Khairkhan (venerated as a sacred site since ancient times) which is towering to a height of 150m over the low river terrace. The age of the brittle friable materials of which it consists is 10 thousand years, but the "evil winds" keep up upthmsting the sand, often producing huge ridges in the near-by pine forests.

Another plainly visible result of the eolian processes in Siberia are thick (of even more than 10m) layers of loess-like loam and sandy loams which cover the slopes of interfluves. They bear a striking resemblance to the famous Chinese loesses with their fine layered structure, reflecting eolian ripples.

Eolian phenomena reach their hight in Eastern Siberia in the spring, early summer and in the autumn- the local dry season.

Years back I had an apartment in the center of the Siberian city of Chita. In spring time, when I came home in the evening, I saw the floors of my rooms covered with a fine layer of whitish dust. It was blown in by

winds and draughts, although all windows were closed. In late June in 1970 in Zabaikalye I happened to see sand drifts 20 to 40 cm high on the edge of a planted field which were blown up in just one spring season. Or take another example of such eolian activity in Siberia: in the aforesaid Tunkinskaya basin the slopes of roadways running through sands are reshaped by winds in one year and covered with eolian ripples...

What catches the eye and is remembered most often are forms of relief and sediments produced by accumulations of sand and dust. And what about the regions of deflation- from where all this sand and dust are blown away? While assessing the general scale of wind activity, one can not ignore this factor also.

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What can we take as a graphic and reliable source of such information? In our jargon we call them "vetrogranniki"-bits and pieces of rock lying on the surface and "ground" by fine sand and dust blown over them. They usually have a typical look: with a flat bottom and two, as if polished, sides, or facets, converging upwards under an obtuse angle, forming clearly visible edges. The surface of the facets is rather unusual, being spongeous (with the softer grains being knocked out) and also polished up at one and the same time. These "wind-facets" stand out from a mass of other debris-looking like arrow-heads or points of spears.

I have in my collection two such samples from different parts of Siberia. I picked up the first one in 1980 during an expedition to the left bank of the Lena, near the town of Zhigansk-right on the line of the Arctic Circle. The beach shingle and pebble there is exposed to strong wind carving, or corrosion, which continues even now so that many bits of rock have been ground into typical traingular "wind-facets".

My second sample comes from the left bank of the Ikhe-Ukhguni in the Tunkinskaya basin. It was buried in a section of eolian sands on the famous Mount Khairkhan. The upper part of this section, or profile, aged 29 thousand years, had been blown away, with the fragments of rock it contained being piled up at the foot of the mount. On the Island of Oikhon in Lake Baikal, especially on its windward north-western slope, "wind-facets" are a common sight, sticking out from under the ground. Such stones are also common on the sandy beaches of the Bratskoye artificial lake. There traces of corrosion can be seen even on primitive stone tools washed out from transects. And one can distinguish upon them both-traces of present-day eolian impacts and also of the pre-historic ones which must have been in progress in Eastern Siberia for hundreds of thousands of years.

Summing up, we know but little about the eolian processes in this region of Eurasia in the past and clearly underestimate their role there today. And the Barguzinsk valley to the east of Baikal has been the starting point of severe sandstorms now and then. During one such storm in May 1996 in the Irkutsk region many local rural settlements were destroyed by fires.

Eolian processes in Siberia are a subject of careful studies with the assistance of the Russian Foundation of Fundamental Research (Grant No. 99-05-65638).

Опубликовано на Порталусе 08 сентября 2018 года

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