Rekonstruksjon av deglasiasjonsforløpet på den nordvestlige delen av Hardangervidda
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The aim in this thesis is to contribute with new information regarding the ongoing debate on whether the Scandinavian Ice Sheet readvanced during the Younger Dryas, filling Hardangerfjorden in Western Norway (as well as other western fjords) with ice, or whether the fjord became ice-free in Allerød or earlier. At the northwestern part of the mountain plateau Hardangervidda, in the inner part of Hardangerfjorden, there are two sharp, semi-parallel moraine ridges belonging to the Eidfjord-Osa Moraine. The moraine has been interpreted as being of Preboreal origin, created after the 2000 m thick Younger Dryas Ice Sheet retreated from the fjord by calving. The Eidfjord-Osa Moraine in my study area was dated by exposure dating on five glacier derived boulders. Two of the samples yielded Preboreal/Boreal ages (10.15 ± 0.50 and 10.14 ± 0.50). The boulders have most likely been buried during and/or after deposition, hence the ages are presumed to be underestimated. One radiocarbon date from a sediment core from a moraine dammed lake yielded a middle Preboreal age (10 789 ± 104 cal. yr BP). Two other radiocarbon ages retrieved from the same lake in 2002 yield late Younger Dryas/early Preboreal age. Two other moraine systems are also observed in the study area. The one situated close to the mountain Berakupen is interpreted as the oldest of the four systems based on morphology and location. The moraine has not been dated, but it is presumed to have been deposited in early Younger Dryas, Older Dryas or even earlier by comparison with the Eidfjord-Osa Moraine. If this is correct, the moraine system would probably have been overridden and destroyed by a the Younger Dryas Ice Sheet heading towards the coast. Hence, the ice sheet was probably thinner than the expected height of 2000 m. Other arguments against the prevailing theory include that the presumed Younger Dryas moraines were deposited by local glaciers instead of an ice sheet, indications of a Younger Dryas marine transgression in inner Hardanger and research suggesting that the Folgefonna plateau glacier did not reach Hardangerfjorden during this cold period. In this thesis it is suggested that the Eidfjord-Osa Moraine most likely is of late Younger Dryas origin. This hypothesis supports the alternative deglaciation model of Hardangerfjorden and the Hardanger region, but a lot of research remain to verify this theory.