Abstract: In geology, permafrost is defined as ground including rocks or soil at or below the freezing point of water 0c for two or more years. Permafrost accounts for 0.022% of total water on Earth and exist in 24% exposed land in Northern Hemisphere. Most Permafrost is located in high latitude ( in and around the Arctic & Antarctic region ).In India Permafrost is located in Tibetan Plateau , Hindu-Kush Himalayan Region , Kullu , Leh region in Jammu & Kashmir . The Permafrost is found in elevation of 2,400 2,800 m, in Himalaya is thawing mainly due to global warming, which contributes to river flood in down-stream area. A collaborative Indo-Swiss research on Permafrost has thrown new light on these rarely studied component of the Indian Himalayan cryosphere. Overall 9 %( 420 sq.Km) of land area in Kullu is classified as Permafrost terrain. Hence Permafrost is classified as significant. Permafrost is not only affected by climate change but eventually will affect climate change itself by releasing the greenhouse gases it stored. More than 50% of modelled permafrost land area in Kullu is characterised by slopes less than 35, a threshold commonly used to distinguish debris-covered slopes from steeper bed rock. Thawing of permafrost in such regions is a potential hazard that could lead to debris instabilities and increased sediment load in water ways and reservoirs. Thawing of permafrost may destabilizelakes, dams and rock-fall or debris flow from surrounding slopes may cause overlapping waves or block outlet channels. If high northern latitude warm significantly permafrost will thaw, allowing organic matter within the permafrost to decompose which release carbon into atmosphere and thus temperature increase. In past 50 years the temperature has increased by 1.3c, 3 times the global average this resulted in 82% retreating of ice covers and 10% degrading of permafrost. Permafrost has crucial effects on environment and Civil structures, because when permafrost melts the land above it sinks or changes shape and the shifting ground could potentially damage building and infrastructure such as roads, Airport, water and sewer pipes. Thus to have spotlight on such crucial topic it is necessary to study permafrost.

Keywords: Permafrost, Qinghai-Tibet Railway, Cooled Road, Thermosyphon.