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单词 tunnel valley
释义
tunnel valley

Geology and Earth Sciences
  • A valley cut by a subglacial stream escaping from beneath an ice sheet. It is well developed in Denmark (where such valleys are called ‘tunneldale’) and in Germany (‘Rinnentaler’). Individual examples may be up to 75 km long and up to 100 m deep, with steep sides and flat floors. The long profile may be irregular, as a result of water under pressure being locally forced uphill, and so the valley may now be occupied by a string of lakes (‘ribbon lakes’).


Geography
  • A large, elongate, overdeepened depression cut into bedrock or glacigenic sediment, up to 4 km wide, over 100 m deep, and 30–100 km long. In long profile they contain enclosed hollows or isolated and elongated basins, sometimes displaying convex-up or undulating longitudinal channel profiles and anabranching channel networks (Beaney (2002) Qt. Int. 90). Ó’Cofaigh (1996, PPG 20) attributes their formation to the creep of deformable subglacial sediment into a subglacial conduit, followed by the removal of this material by meltwater flow.


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