| 1. |
- Heyman, Jakob, et al.
(författare)
-
Morphology, distribution and formation of relict marginal moraines in the Swedish mountains
- 2006
-
Ingår i: Geografiska Annaler: Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 88A:4, s. 253-265
-
Tidskriftsartikel (refereegranskat)abstract
- Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque-and-valley moraines, valley-side moraines, complex moraines and cross-valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice-sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice-sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation.
|
|
| 2. |
- Hall, Adrian M., et al.
(författare)
-
Glacial ripping: geomorphological evidence from Sweden for a new process of glacial erosion
- 2020
-
Ingår i: Geografiska Annaler Series a-Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 2:4, s. 333-53
-
Tidskriftsartikel (refereegranskat)abstract
- In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultantboulder spreadsare covers of large, angular boulders, many with glacial transport distances of 1-100 m. Boulder spreads occur alongside partly disintegrated roches moutonnees and associated fracture caves, and are associated withdisrupted bedrock, which shows extensive fracture dilation in the near surface. These features are distributed in ice-flow parallel belts up to 10 km wide and extend over distances of >500 km. Our hypothesis is that the assemblage results from (1) hydraulic jacking and bedrock disruption, (2) subglacial ripping and (3) displacement, transport and final deposition of boulders. Soft sediment fills indicate jacking and dilation of pre-existing bedrock fractures by groundwater overpressure below the ice sheet. Overpressure reduces frictional resistance along fractures. Where ice traction overcomes this resistance, the rock mass strength is exceeded, resulting in disintegration of rock surfaces and ripping apart into separate blocks. Further movement and deposition create boulder spreads and moraines. Short boulder transport distances and high angularity indicate that glacial ripping operated late in the last deglaciation. The depths of rock mobilized in boulder spreads are estimated as 1-4 m. This compares with 0.6-1.6 m depths of erosion during the last glaciation derived from cosmogenic nuclide inventories of samples from bedrock surfaces without evidence of disruption. Glacially disrupted and ripped bedrock is also made ready for removal by future ice sheets. Henceglacial rippingis a highly effective process of glacial erosion.
|
|
