Permafrost is permanently frozen ground, including soil, sediment, or rock. To be considered permafrost, the ground must remain below freezing for at least two consecutive years and can last for tens of thousands of the year. Therefore, permafrost can directly relate to climate and temperature variation. However, it also depended on geologic, hydrologic, topographic and botanical features. The known permafrost thickness ranges from 1500m in Siberia to less than 1m at the southern boundary of the permafrost zone. Permafrost can be found several places on Earth, however, generally in high latitudes near the North and South Poles. More or less, half of the world’s permafrost in Russia and Siberia, and the largest extent of mountain permafrost is on the Tibetan Plateau.
- Encyclopedia of Global Environmental Change, published in 2002, John Wiley & Sons.