Timing and sequential evolution of one of Northern Europe`s largest canyons: Jutulhogget, central Southern Norway

At the end of the last deglaciation, the ice divide of the Scandinavian ice sheet was located south of main watershed of southern Norway. Consequently, water was dammed between the melting ice sheet and the main watershed. As overflow gaps across the main watershed became ice free at progressively lower altitudes, glacier dammed lakes of different elevation and extension came into existence. The latest and largest of these glacier dammed lakes was Nedre Glomsjø with a length of more than 100 km and a volume exceeding 100 km3. Nedre Glomsjø had its outlet at Rugldalen, 665 m above sea level (m a.s.l.), conveying the water to Gauldal and Trøndelag. This lake covered three adjacent valleys: Østerdalen, Tylldal and Rendalen. The ice dam collapsed first in Rendalen. The water from Østerdalen had to cross the shallow crest of a hill between the two valleys and a large canyon was carved out by the cataclysmic water flood. This canyon called Jutulhogget, is 2.5 km long, up to 250 m deep and has a width in the range of 100 to 500 m. In Østerdalen, upstream of Jutulhogget canyon, shorelines and delta terraces exist in at least 4 levels between 665 m a.s.l. and 510 m a.s.l. which is the present elevation of the headwall of Jutulhogget (the overflow gap). In the other two valleys (downstream the canyon) only shorelines at 665 m a.s.l., the original lake Nedre Glomsjø, exist. Shorelines can only form in glacier dammed lakes, if their outlet is over solid rock. This has led to a widely accepted theory of evolution of the canyon through a series of drainage events. However, it is still unknown whether this happened several times during the deglaciation or if the canyon existed prior to the late LGM (last glacial maximum, about 20 ka BP). In the latter case, preservation of shorelines and delta terraces has been explained by the fact that this area of Norway was covered by non-erosive, cold based ice (i.e. glacier frozen to the ground). A characteristic flood sediment was deposited south of the (at that time) remnant ice sheet. This deposit occur in such an extent that it has been linked to the drainage event of the glacier dammed lake Nedre Glomsjø. The deposition has been dated to Preboreal (9100±100 14C years or about 10 200 calendar years BP). As only one single flood deposit is observed, it has suggested that Nedre Glomsjø was drained only once during the deglaciation. Sediment samples from delta terraces at different elevations have been collected for optically stimulated luminescence (OSL) dating. Preliminary results indicate at least two drainage events of lake Nedre Glomsjø across Jutulhogget during the deglaciation; possibly one during early Preboreal (c. 11.2 ± 1.2 ka BP) and another one during late Preboreal (10.4 ± 0.8 ka BP). The last drainage event relates to the present elevation of the outlet at Jutulhogget and the timing corresponds with the depositon of the flood sediment at the distal side of the ice sheet.