RosegおよびTschierva氷河の後退 : 空中写真判読および図化による測定
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It is well known that glaciers in Europe have been remarkably retreating in recent period according to the climatic change. Roseg and Tschierva Glacier, descending northwest slope of Mt. Bernina (4, 049 m), eastern Swiss Alps, as a typical valley glacier system, is one of the example.<BR>The author had a chance in his cartographic research at Zurich Technical University (ETH) to compile a topographical map of glacier, using the aerial photographs taken by Swiss Federal Topographic Survey (Eidge. Landestopographie) in 1971, and to compare it with the other topographical maps which are showing glacial conditions in 1934, 1955 and 1964 respectively.<BR>As the result of comparison, it is recognized that the ice tongue of Roseg Glacier has been retreated about 1, 000 m in 37 years from 1934 to 1971, while the ice tongue of Tschierva Glacier has been retreated about 800 m in the same period.<BR>Behind the retreated Tschierva glacial tongue, undulating features of ground moraine are left in the form of river terraces according to the erosion by melted water. Lateral moraines at the both sides of the glacier have been built up as remarkable dykes with steep slopes and knife ridges, they have been, however, suffered from vigorous gully erosion on their slopes after the retreat of ice tongue. As the result of erosion, location of knife ridges were shifted outward. Especially on the left dyke the shift of ridge was reached about 70 m.<BR>Since this left dyke of lateral moraine had been built as a huge crossing barrier over Roseg glacial valley, a large glacial lake was formed in Roseg valley in consequence of dam up of melted water from the glacial tongue.<BR>In Tschierva glacial valley, half ring shaped features of old terminal moraine are recognized at the altitude of 2060 to 2070 m. According to Professor E. Spiesss opinion, these features have been formed by old glacial tongue in 1850 and are covered by bushes of Rhododendron juniperus nana. While on the ground moraine there are scarcely recognized vegetations on the aerial photographs taken in 1971. These facts perhaps show that the retreat of Tschierva Glacier amount to about 1, 000 m during the period from 1850 to 1971 has been occured not gradually and continuously but suddenly after relatively long stable period. The author considers that the retreat of about 800 m, which is the greater part of total volume has been occured in recent 37 years.<BR>On both mountain slopes of Roseg Glacier there are old moraine terraces which have been built in Ice Age. They keep still flat surfaces but their flanks present singular sight of badland and supply large quantity of detritus to make talus scarp.<BR>Two block-stream features are recognized on the gentle slope of Mt. Aguagliouls.They are considered as successors of former ground moraines.<BR>The author would like to thank Prof. E. SPIESS, Associate Prof. Ch. HOINKES and Mr. F. FURRER in Zurich Technical University for their guidance and assistance. And he is also indebted to Swiss Federal Topographic Survey for the permission to reproduce topographical map and aerial photographs.
- 社団法人 東京地学協会の論文