The Earth’s climate periodically undergoes serious changes associated with alternating large-scale cooling, accompanied by the formation of stable ice sheets on the continents, and warming. The last ice age, which ended about 11-10 thousand years ago, is called the Valdai glaciation for the territory of the East European Plain.
Systematics and terminology of periodic cooling
The longest stages of general cooling in the history of the climate of our planet are called cryoers, or glacial eras up to hundreds of millions of years old. At present, about 65 million years have passed on Earth and, apparently, will continue for a very long time (judging by previous similar stages) the Cenozoic cryoera.
Throughout the eras, scientists distinguish ice ages alternating with phases of relative warming. Periods can last millions and tens of millions of years. The modern ice age is Quaternary (the name is given in accordance with the geological period) or, as it is sometimes said, Pleistocene (according to a smaller geochronological unit - era). It began about 3 million years ago and, apparently, is still far from complete.
In turn, ice ages consist of shorter - several tens of thousands of years - ice ages, or glaciations (the term “glacial” is sometimes used). Warm gaps between them are called interglacials, or interglacials. We now live precisely during such an interglacial era, which replaced the Valdai glaciation on the Russian Plain. Glaciations in the presence of undoubted common features are characterized by regional features, so they get names for this or that locality.
Within eras, stages (stadia) and interstadials are distinguished, during which the climate experiences the most short-term fluctuations - pessimums (cooling) and optima. Currently, it is characterized by the climatic optimum of the sub-Atlantic interstadial.
The age of the Valdai glaciation and its phase
According to the chronological framework and conditions of separation at the stage, this glacier is somewhat different from Wurm (Alps), Wislinsky (Central Europe), Wisconsin (North America) and other cover glaciations corresponding to it. On the East European Plain, the beginning of the era that replaced the Mikulin interglacial dates back to about 80 thousand years ago. It should be noted that the establishment of clear timelines presents a serious difficulty - as a rule, they are blurred - therefore, the chronological framework of the stages varies significantly.
Most researchers distinguish two stages of the Valdai glaciation: it is Kalinin with maximum ice about 70 thousand years ago and Ostashkovskaya (about 20 thousand years ago). The Bryansk interstadial separates them - warming, which lasted from about 45–35 to 32–24 thousand years ago. Some scholars, however, offer a more fragmented division of the era - up to seven stages. As for the retreat of the glacier, it happened over the period from 12.5 to 10 thousand years ago.
Glacier geography and climatic conditions
The center of the last glaciation in Europe was Fennoscandia (includes the territories of Scandinavia, the Gulf of Bothnia, Finland and Karelia with the Kola Peninsula). From here, the glacier periodically expanded to the south, including the Russian Plain. It was less extensive in scope than the preceding Moscow glaciation. The border of the Valdai ice sheet passed in the northeast direction and did not reach a maximum of Smolensk, Moscow, Kostroma. Then, on the territory of the Arkhangelsk region, the border steeply turned north to the White and Barents Seas.
In the center of glaciation, the thickness of the Scandinavian ice sheet reached 3 km, which is comparable with the thickness of the ice in Antarctica. The glacier of the East European Plain had a thickness of 1-2 km. Interestingly, with much less developed ice cover, the Valdai glaciation was characterized by severe climatic conditions. The average annual temperatures during the last glacial maximum - Ostashkovsky - only slightly exceeded the temperatures of the era of the very powerful Moscow glaciation (-6 ° C) and were 6-7 ° C lower than modern ones.
Consequences of glaciation
The traces of the Valdai glaciation, which are widespread on the Russian Plain, testify to the strong influence it had on the landscape. The glacier erased many of the bumps left by the Moscow glaciation, and formed during its retreat, when a huge amount of sand, debris and other inclusions melted from the mass of ice, deposits up to 100 meters thick.
The ice cover was advanced not by a continuous mass, but by differentiated flows, along the sides of which piles of clastic material — edge moraines — were formed. These are, in particular, some ridges within the present Valdai Upland. In general, the entire plain is characterized by a hilly moraine surface, for example, a large number of drumlins - low elongated hills.
Very visible traces of glaciation are lakes formed in hollows plowed by a glacier (Ladoga, Onega, Ilmen, Chudskoe and others). The river network of the region also acquired a modern look as a result of exposure to the ice sheet.
The Valdai glaciation changed not only the landscape, but also the composition of the flora and fauna of the Russian Plain, influenced the area of settlement of ancient people - in a word, it had important and multifaceted consequences for this region.