GLACIAL LAND FORMS INDICATIVE OF A PARTLY FROZEN BED

In parts of the core area of the Fennoscandian ice sheet relict perigl acial surfaces occur. The boundary between periglacial and glacial lan dscapes is often sharp and erosional, with fluting truncating patterne d ground. The periglacial surfaces are older than the last ice sheet a nd are interpreted to represent patches of continuous frozen-bed condi tions. A specific land-form assemblage occurs at the edges of such pat ches. On the basis of three type localities along the eastern rim of t he Scandinavian mountains, four thermal boundary land forms, character istic of the frozen-patch environment, are defined. Stoss-side moraine s and transverse till scarps, not previously described, are interprete d to have formed in detachment zones where soil frozen to the glacier overlies thawed soil. The detachment zones are located where subglacia l warming raises the phase-change surface (water/ice) until it interse cts the soil layer up- and down-glacier from residual frozen-bed patch es. The up-glacier ends of frozen-bed patches are located on topograph ic highs, but down-glacier the location of lateral sliding boundaries is occasionally independent of topography. The identification of relic t surfaces and thermal boundary forms can improve paleo-ice-sheet mode ls by providing estimates of the extent of frozen-bed conditions.