A NEW CONCEPTUAL MODEL FOR THE DEVELOPMENT OF THE CANYON JUTULHOGGET, SOUTH-NORWAY

Jutulhogget in central South-Norway is a 2.5 km long canyon with an amphi-theatered headwall of more than 100 m. The canyon was carved out by glacier dammed outburst floods (GLOFs) during deglaciation events. During the late Weichselian (the last glaciation in Scandinavia) the main ice divide in South-Norway was situated south of the main watershed. Consequently, meltwater was trapped in large, glacier dammed lakes in the upper part of the south-trending valleys. The latest and largest of these lakes was Lower Glåmsjø, which was more than 120 km long and filled-up three adjacent valleys. The ice-dam broke first in the smaller but deeper valley, and all the water from the largest valley system had to cross a narrow ridge where the canyon was carved out.

The paradox of the development of Jutulhogget canyon is that only one single flood deposit is observed at the proximal side of the remnant ice-sheet, while in the valleys upstream of Jutulhogget shorelines are present at different altitudes between the overflow gap towards north and the present overflow gap at Jutulhogget. Previously, these observations have been explained by one single drainage event during the last deglaciation and that the canyon existed prior to the last glacial maximum while the older shorelines have been preserved bellow a cold-based ice sheet that was frozen to the ground.

New survey of the flood deposits and erosional landforms in direct relation to the canyon has revealed much more details about the GLOFs and the canyon development. Plunge pools, terrace deposits at different altitudes, sub-aerial meltwater channels, glacio-lacustrine deposits, ice-contact surfaces and dead-ice terrain are among the features that have been surveyed in close detail. We suggest a series of drainage events during the deglaciation with various degree of ice-contact, and separated by phases of sub-aerial drainage and refilling of the glacier dammed lake.