Ploughing blocks of the Tien Shan

• Published in: Permafrost and Periglacial Processes
• Main Author: Gorbunov, A. P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1991
• Subjects: Permafrost and Periglacial Processes
• Online Access: http://dx.doi.org/10.1002/ppp.3430020307; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fppp.3430020307; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppp.3430020307

Abstract Ploughing blocks (boulders) consist of three elements, namely, a rock fragment, a mound and an elongate depression. The movement of a block downslope leads to the formation of a pressure mound ahead of the block, while in its rear there is a furrow. In the Tien Shan mountains the size of the largest ploughing block is ≈11 m 3 , the height of the largest mound is about 1.0 m and the most elongated furrow is ≈37 m long. Seasonally frozen ground below the blocks or in their immediate vicinity gives rise to their movement. Seasonal freezing is the key factor that dictates a high ice content and ground moisture beneath the block which causes the gliding downslope. The block movement velocity is not regular and reaches its maximum in the second half of spring. Velocity varies also from year to year: in certain years it is nil and sometimes it is high as 7‐10 cm a year.