Ledoyom
Encyclopedia
Ledoyom is a term proposed by the Russian geologist V.P. Nekhoroshev for intermontane depressions which might get completely filled by glaciers from the surrounding mountains at the maxima of glaciation.
In the 1930s the Russian geologist V.P. Nekhoroshev marked out intermontane depressions in the Altai which might get completely filled by glaciers from the surrounding mountains at the maxima of glaciation. He called such depressions "ledoyoms". The Russian term “Ledoyom (ледоём)” means an “ice body” by analogy with a “water body”. Ledoyoms produced large valley glacier
s within outlet runoff valleys from the depressions at culmination stages of their development. Diagnostic marks of the so-called classical ledoyoms are moraine
s, esker
s and kame
s on the bottoms of the corresponding depressions.
In the 80-s and 90-s the Russian geologist Alexei Rudoy of glacier-dammed lakes which used to fill most of the inter-montane basins of the mountain belt of Siberia
, the depressions of Teletskoye and Baikal
lakes including, took place. It also became clear that many depressions, even very large ones, had been already occupied by dammed water basins by the time when the glaciers of the mountain frame moved forward into them. Thus, mountain glaciers turned into original “shelf
” glaciers and armored completely the surface of the glacier-dammed lake joining together floating on the surface. That is the way the so-called “captured lakes” came to exist.
At maximum lowering of the snow-line (in the Altai and the Sayan
its depression gave about 1200 m in late pleistocene
) some of the lakes (Chuya, Kuray, Uymon and others) began functioning in an under-ice regime because they never got free from ice for thousands of years. Such lakes turned into ice bodies of the “aufeis
” type. They consisted of a thick lens of lake water, which was covered by lake ice
, aufeis
and glacier
ice, and by snow
-firn
sequence, too. “Aufeis” ledoyoms became independent centers of glaciation with subradial ice outlets. Possible analogies of such an evolution mechanism and pre-glacial lakes are thick water lenses under a 3-4 kilometer-thick unit of the glacier cover at the sites of Dome B and Dome Charlie and the Vostok Station
in Eastern Antarctica.
Thus, depending on the intermontane depression topography, the values, of the snow-line depression and of the glaciation energy, the interrelation of the glaciers and the ice-dammed lakes in the mountains of south
of Western Siberia
could develop according to the following scenarios: (1) A ledoyom only (no ice-dammed lake). In such cases some glacial and water-glacial relief forms and sediments would remain in the basins; (2) A water body and a ledoyom together (the stage of “catch lakes”). Certain forms of “dead ice” may remain in the basins, as well as intraglacial water-ice forms - eskers and kames which were projected onto the bottom lake deposits when the “shelf” ice descended; (3) “Aufeis” ledoyoms; (4) An ice-dammed lake only.
Under different extensions of the glacier
at different time periods, one and the same basin underwent different sequences of the lake-glacier events.
In the 1930s the Russian geologist V.P. Nekhoroshev marked out intermontane depressions in the Altai which might get completely filled by glaciers from the surrounding mountains at the maxima of glaciation. He called such depressions "ledoyoms". The Russian term “Ledoyom (ледоём)” means an “ice body” by analogy with a “water body”. Ledoyoms produced large valley glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s within outlet runoff valleys from the depressions at culmination stages of their development. Diagnostic marks of the so-called classical ledoyoms are moraine
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
s, esker
Esker
An esker is a long winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America...
s and kame
Kame
A kame is a geological feature, an irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier, and is then deposited on the land surface with further melting of the glacier...
s on the bottoms of the corresponding depressions.
In the 80-s and 90-s the Russian geologist Alexei Rudoy of glacier-dammed lakes which used to fill most of the inter-montane basins of the mountain belt of Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, the depressions of Teletskoye and Baikal
Baikal
Baykal commonly refers to Lake Baikal in southern Siberia, Russia.Baykal or Baikal may also refer to:-Russia:*Baykal, Irkutsk Oblast, an urban-type settlement*Baykal, Aurgazinsky District, Republic of Bashkortostan, a village...
lakes including, took place. It also became clear that many depressions, even very large ones, had been already occupied by dammed water basins by the time when the glaciers of the mountain frame moved forward into them. Thus, mountain glaciers turned into original “shelf
Shelf
Shelf may refer to:* Shelf , a flat horizontal surface used for diplay and storage* Shelf , a user interface feature in the NeXTSTEP operating system* Shelf, West Yorkshire, a village in England...
” glaciers and armored completely the surface of the glacier-dammed lake joining together floating on the surface. That is the way the so-called “captured lakes” came to exist.
At maximum lowering of the snow-line (in the Altai and the Sayan
Sayan Mountains
The Sayan Mountains are a mountain range between northwestern Mongolia and southern Siberia, Russia.The Eastern Sayan extends from the Yenisei River at 92° E to the southwest end of Lake Baikal at 106° E...
its depression gave about 1200 m in late pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
) some of the lakes (Chuya, Kuray, Uymon and others) began functioning in an under-ice regime because they never got free from ice for thousands of years. Such lakes turned into ice bodies of the “aufeis
Aufeis
Aufeis is a sheet-like mass of layered ice that forms from successive flows of ground water during freezing temperatures. This form of ice is also called overflow, icings, or the Russian term, naled. According to E. de K. Leffingwell the term was first used in 1859 by A. T...
” type. They consisted of a thick lens of lake water, which was covered by lake ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, aufeis
Aufeis
Aufeis is a sheet-like mass of layered ice that forms from successive flows of ground water during freezing temperatures. This form of ice is also called overflow, icings, or the Russian term, naled. According to E. de K. Leffingwell the term was first used in 1859 by A. T...
and glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
ice, and by snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
-firn
Firn
Firn is partially-compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé. It is ice that is at an intermediate stage between snow and glacial ice...
sequence, too. “Aufeis” ledoyoms became independent centers of glaciation with subradial ice outlets. Possible analogies of such an evolution mechanism and pre-glacial lakes are thick water lenses under a 3-4 kilometer-thick unit of the glacier cover at the sites of Dome B and Dome Charlie and the Vostok Station
Vostok Station
Vostok Station was a Russian Antarctic research station. It was at the southern Pole of Cold, with the lowest reliably measured natural temperature on Earth of −89.2 °C . Research includes ice core drilling and magnetometry...
in Eastern Antarctica.
Thus, depending on the intermontane depression topography, the values, of the snow-line depression and of the glaciation energy, the interrelation of the glaciers and the ice-dammed lakes in the mountains of south
South
South is a noun, adjective, or adverb indicating direction or geography.South is one of the four cardinal directions or compass points. It is the opposite of north and is perpendicular to east and west.By convention, the bottom side of a map is south....
of Western Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
could develop according to the following scenarios: (1) A ledoyom only (no ice-dammed lake). In such cases some glacial and water-glacial relief forms and sediments would remain in the basins; (2) A water body and a ledoyom together (the stage of “catch lakes”). Certain forms of “dead ice” may remain in the basins, as well as intraglacial water-ice forms - eskers and kames which were projected onto the bottom lake deposits when the “shelf” ice descended; (3) “Aufeis” ledoyoms; (4) An ice-dammed lake only.
Under different extensions of the glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
at different time periods, one and the same basin underwent different sequences of the lake-glacier events.