The Altai flood refers to the cataclysmic

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

(s) that, according to some geomorphologists, swept along the

Katun River The Katun ( ; ) is a river in the Altai Republic and the Altai Krai of Russia. It forms the Ob as it joins the Biya some southwest of Biysk.

in the Russian Altai (

Altai Republic The Altai Republic, also known as the Gorno-Altai Republic, is a republic of Russia located in southern Siberia. The republic borders Kemerovo Oblast to the north, Khakassia to the northeast, Tuva to the east, Altai Krai to the west, as well ...

and

Altai Krai Altai Krai (, ) is a federal subject of Russia (a krai). It borders, clockwise from the west, Kazakhstan ( East Kazakhstan Region, Abai Region and Pavlodar Region), Novosibirsk and Kemerovo, and the Altai Republic. The krai's administrative ce ...

) at the end of the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

. These

glacial lake outburst flood A glacial lake outburst flood (GLOF) is a type of outburst flood caused by the failure of a dam containing a glacial lake. An event similar to a GLOF, where a body of water contained by a glacier melts or overflows the glacier, is called a j� ...

s were the result of periodic sudden ruptures of ice dams like those triggering the Missoula floods.

Background

In the US, large glacial

outburst flood In geomorphology, an outburst flood—a type of megaflood—is a high-magnitude, low-frequency catastrophic flood involving the sudden release of a large quantity of water. During the last deglaciation, numerous glacial lake outburst floods were ...

s have been researched since the 1920s. In the 1980s, Russian geologists discovered large deposits created through similar catastrophic outbursts of

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

giant glacier-dammed lakes in inter-montane basins of the Altai Mountain range. The largest of these lakes (the conjoined Chuya and Kuray) had a water volume of 600 cubic kilometers when it burst.

Deposits

Gravel dunes

Giant current ripples Giant current ripples (GCRs), also known as giant gravel bars or giant gravel dunes, are a form of subaqueous dune. They are active channel topographic forms up to 20 m high, which occur within near-thalweg areas of the main outflow routes created ...

, (gravel wave trains, gravel dunes and

antidune An antidune is a bedform found in fluvial and other channeled environments. Antidunes occur in supercritical flow, meaning that the Froude number is greater than 1.0 or the flow velocity exceeds the wave velocity; this is also known as upper flo ...

s) up to 18 meters high and 225 meters in wavelength were created in several locations along the lake bottom. They are best developed just east of the Tyetyo River in the eastern part of the Kuray Basin, but several other smaller fields of giant current ripples also occur there. They are made up of rounded pebble gravel.

Giant point bars

Giant bars are found along the lower Chuya and the Katun rivers, rising as much as 300m above modern river levels, with lengths up to five kilometers. Well-developed on the Katun River below its confluence with the Chuya River, the bars appear to have formed as giant

point bar A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on ...

s on the inner bends of the river, paralleling the scoured bare bedrock walls of the cut bank on the outer bends. These bars diminish in height and thickness downstream to about 60 m near Gorno-Altaisk. Some of these giant point bars have formed lakes behind them where they block tributaries of the Katun river. Diluvial bars in Central Altay Mountains July 2011 by Alexei Rudoy

Diluvial bars in Central Altay Mountains July 2011 by Alexei Rudoy

Suspension gravels

Much of the gravel deposited along the Katun valley lacks a stratigraphic structure, showing characteristics of a deposition directly after suspension in a turbulent flow.

Ice-rafted blocks

Ice-rafted boulders up to several meters in diameter exist in the area.

Eddy deposits

Eddy deposits are seen along the Katun River between Inya and Mali Yaloman.

The current understanding

Towards the end of the last glacial period, 12,000 to 15,000 years ago, glaciers descending from the Altai mountains dammed the Chuya River, a large tributary of the Katun River, creating a large glacial lake including the Chuya and the Kurai basins. As the lake grew larger and deeper, the ice dam eventually failed, causing a catastrophic flood that spilled along the Katun River. Its magnitude has been estimated to be similar to that of the Missoula flood in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Timing

The precise timings of the several catastrophic flooding events are not tightly constrained. The mechanisms of lake filling and ice dam failure would suggest an early or late glacial time, whereas conditions at glacial maxima would seem to preclude such events. The catastrophic flood(s) occurred between 12000 BC and 9000 BC. Most of the water discharge is thought to have occurred during one day, with peak discharges of 10⁷ m³/s (Herget, 2005). The maximum lake volume was 6x10¹¹ m³ (600 km³) with an area of 1.5x10⁹ m². The ice dam was about 650 m high.

Flood route

When the ice dam failed, floodwaters coursed down the Chuya River to the confluence with the Katun River, followed the Katun into the Ob River, and then into

Lake Mansi The West Siberian Glacial Lake, also known as West Siberian Lake () or Mansiyskoe Lake (, Mansi Lake), was a periglacial lake formed when the Arctic Ocean outlets for each of the Ob River, Ob and Yenisei River, Yenisei rivers were blocked by the B ...

, a large proglacial Pleistocene lake, ~600,000 km² in area. The fast inflow raised its level by only ~12 m but some authors argue that, because the Turgay spillway of Lake Mansi was only 8 m above the lake level at the time, much of the floodwater continued into the

Aral Sea The Aral Sea () was an endorheic lake lying between Kazakhstan to its north and Uzbekistan to its south, which began shrinking in the 1960s and had largely dried up into desert by the 2010s. It was in the Aktobe and Kyzylorda regions of Kazakhst ...

. From there the flooding waters may have followed through the Uzboy spillway into the

Caspian Sea The Caspian Sea is the world's largest inland body of water, described as the List of lakes by area, world's largest lake and usually referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, ...

, then through the Manych spillway into the

Black Sea The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bound ...

, and eventually into the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

.Grosswald, M.G., 1998, New approach to the ice age paleohydrology of northern Eurasia. Chapter 15. (P. 199-214)— Palaeohydrology and Environmental Change / Eds: G. Benito, V.R. Baker, K.J. Gregory. — Chichester: John Wiley & Sons Ltd, 1998. 353 p.

References

External links

Lee, 2004, The Altay Flood

Alexei N. Rudoy, 2005. Giant current ripples (History of the Research, their diagnostics and palaeogeographical significance). - Tomsk. - 224 pp. In Russian, Eng. summary: pp. 134-211 pp.
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