In Russia, permafrost covers two-thirds of the territory. In summer, the upper layer thaws up to a few meters, causing the soils to "float". In winter, it freezes back. As a result, unusual landscapes are formed. In Taimyr, Yakutia, and Chukotka, one can see polygonal tundras. Sometimes they are referred to as square marshes. Over thousands of years, the soil froze in winter and shrank in volume, cracking, and in summer it filled with water, gradually growing into the ground with narrow veins of ice extending dozens of meters deep. Pleistocene ices are also formed, meaning whole layers of continuous ice, separated by layers of soil. Scientists believe that in recent years, the permafrost is thawing deeper than before, by several centimeters per decade. Thawing is caused both by the greenhouse effect and human activities. "And the more permafrost thaws, the higher the temperature and even more permafrost thaws. It's a vicious circle," says hydrologist Nikita Tananaev from the Permafrost Institute in Yakutsk. In the long term, the average annual temperature is gradually increasing. Residents of northern regions often say that in their childhood, the frosts were harsher and longer.