50°17′07″N 87°40′16″E  /  50.28528°N 87.67111°E  / 50.28528; 87.67111

The Altai flood refers to the huge flood(s) that, according to some scientists who study Earth's features, occurred along the Katun River in the Russian Altai (Altai Republic and Altai Krai) at the end of the last ice age. These floods happened because large amounts of water from glacial lakes suddenly broke through ice dams, similar to the Missoula floods.

Background

In the United States, scientists have studied large floods caused by glaciers since the 1920s. In the 1980s, Russian geologists found large deposits of material left by sudden and powerful floods from ancient lakes that were blocked by glaciers in the Altai Mountain range. The largest of these lakes, the combined Chuya and Kuray lakes, held 600 cubic kilometers of water when it burst.

Deposits

Giant current ripples, including gravel wave trains, gravel dunes, and antidunes, up to 18 meters high and 225 meters long, were formed in several places on the lake bottom. These features are most clearly seen just east of the Tyetyo River in the eastern part of the Kuray Basin, though smaller areas of similar ripples also exist there. These ripples are made of rounded pebble gravel.

Giant bars are found along the lower Chuya and Katun rivers, reaching heights of up to 300 meters above current river levels and stretching as far as five kilometers. On the Katun River below where it meets the Chuya River, these bars appear to have formed as large point bars on the inside curves of the river, running parallel to the exposed bedrock walls on the outside curves. These bars become smaller and thinner as they extend downstream, reaching about 60 meters near Gorno-Altaisk. Some of these large point bars have created lakes by blocking tributaries of the Katun River.

Much of the gravel found in the Katun valley does not show a layered structure, suggesting it was deposited quickly after being carried in a turbulent flow.

Large boulders, some several meters in diameter, were transported by ice and left in the area.

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

Latest research

At the end of the last ice age, between 12,000 and 15,000 years ago, glaciers from the Altai Mountains blocked the Chuya River, a major branch of the Katun River, forming a large glacial lake that covered the Chuya and Kurai basins. As the lake expanded, the ice dam that held it eventually broke, causing a massive flood that released water into the Katun River. This flood was as large as the Missoula flood in North America.

The exact timing of the flood events is not fully known. The way the lake filled and the ice dam collapsed suggest the flood may have happened early or late in the glacial period, but conditions during the peak of the ice age likely prevented such events. The flood(s) occurred between 12,000 BC and 9,000 BC.

Most of the water was released in one day, with the highest flow reaching 10 cubic meters per second. The lake’s maximum volume was 6 billion cubic meters (600 cubic kilometers), covering an area of 1.5 billion square meters. The ice dam was approximately 650 meters tall.

When the dam broke, floodwaters flowed down the Chuya River to where it meets the Katun River. The water then moved into the Ob River and into Lake Mansi, a large lake from the Pleistocene era, which covered about 600,000 square kilometers. The sudden increase in water raised Lake Mansi’s level by about 12 meters. Some scientists believe that because Lake Mansi’s Turgay spillway was only 8 meters above the lake’s level at the time, much of the floodwater may have continued into the Aral Sea. From there, the water could have traveled through the Uzboy spillway into the Caspian Sea, then through the Manych spillway into the Black Sea, and finally into the Mediterranean Sea.