tunnel valley 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’).

tunnel valley 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 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’).