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A stone run (called also ''stone river'', ''stone stream'' or ''stone sea''〔(Vitosha Nature Park: Basic Information. Landscape. ) Vitosha Nature Park website.〕) is a conspicuous rock landform, result of the erosion of particular rock varieties caused by myriad freezing-thawing cycles taking place in periglacial conditions during the last Ice Age. The actual formation of stone runs involved no less than five processes: weathering, solifluction, frost heaving, frost sorting, and washing.〔Stone, Phillip. (Periglacial Princes Street - 52° South. ) ''The Edinburgh Geologist''. Issue No 35, 2000.〕 The stone runs are essentially different from moraines, rock glaciers, and rock flows or other rock phenomena involving the actual flow of rock blocks under stress that is sufficient to break down the cement or to cause crushing of the angularities and points of the boulders.〔Harris, Stuart A. (Climatic Zonality of Periglacial Landforms in Mountain Areas. ) ''Arctic'', Vol. 47, No. 2, June 1994, pp. 184-92.〕 By contrast, the stone run boulders are fixed quite stably, providing for safer climbing and crossing of the run. Stone runs are accumulations of boulders with no finer material between them. In the Falklands, they occur on slopes of between 1 and 10 degrees, and are the product of mass-movement and stone sorting during past periods of cold climate. They everywhere occur in association with poorly sorted, clay-rich solifluction deposits 〔ALDISS, D T, and EDWARDS, E J. 1999. The Geology of the Falkland Islands. British Geological Survey Technical Report, WC/99/10.〕 ==Geographic distribution== Best known for their exceptional diversity, size and abundance are the stone runs of the Falkland Islands, and the stone rivers of Vitosha Mountain, Bulgaria. The highly specific combination of particular climatic conditions and rock varieties that existed there during the Quaternary explains both the formation of stone runs in those two territories, and their absence in areas with otherwise comparable nature conditions. For instance, while the present Falklands climate is quite similar to that of Scotland the latter was completely glacial rather than periglacial during the relevant period, which would not allow for the formation of stone runs. On the other hand, due to geological and other specifics of the southern temperate and sub-Antarctic territories with climatic history similar to that of the Falklands (Prince Edward Islands, Crozet Islands, Kerguelen Islands, Macquarie Island, Campbell Islands, or nearby Tierra del Fuego and Patagonia), none of them features landforms even remotely comparable to the Falklands stone runs.〔Hall, Kevin.(Review of Present and Quaternary periglacial processes and landforms of the maritime and sub-Antarctic region ). ''South African Journal of Science'', Vol. 98, January/February 2002. pp. 71-81.〕 Likewise, the specific geology of Vitosha accounts for the fairly restricted examples of similar landforms in other Bulgarian or indeed Balkan mountains with comparable climatic record among which Vitosha is one of the smallest, extending just by . However, even on that small territory the stone runs exist along with screes and other rock landforms, suggesting that the right periglacial conditions and rock composition are necessary but not sufficient conditions for the formation of stone runs.〔(''Vitosha Nature Park: Management Plan 2005-2014''. ) Ministry of Environment and Waters, Sofia, 2005. (in Bulgarian).〕 Other examples of stone runs occur in England, most notably at the Stiperstones, Shropshire.〔GOUDIE, A S, and PIGGOTT, N R. 1981. Quartzite tors, stone stripes, and slopes at the Stiperstones, Shropshire, England. Biuletyn Periglacjalny, Vol. 28, 47-56.〕〔CLARK, R. 1994. Tors, rock platforms and debris slopes at Stiperstones, Shropshire, England. Field Studies, Vol. 8, 451 - 472.〕 They are also known in Pennsylvania.〔SMITH, H T U. 1953. The Hickory Run boulder field, Carbon County, Pennsylvania. American Journal of Science, Vol. 251, 625-642.〕 Small examples are probably very widespread where solifluction deposits contain large concentrations of frost-resistant rock blocks. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「stone run」の詳細全文を読む スポンサード リンク
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