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The Main Line is a conspicuous late glacial erosive feature along parts of the Norwegian coastline. Although the shoreline has been much studied, the genesis of the ancient raised sea-level is still somewhat unaccounted for. In this study, the Main Line on Leka, Norway, is illuminated through a high resolution (1 m pixel size) digital elevation model (DEM) derived from airborne LiDAR data. The DEM allows a detailed mapping of the shoreline's dimensions and actual distribution and hence provides an improved foundation for interpreting the pronounced features. A new method for estimating cliff degradation during shoreline formation is presented. The Main Line is found from 106–112 m asl on Leka. Varying platform morphology across the island points to different shore-eroding mechanisms. The shoreline is thought to be developed through the interaction of sea–ice processes and freeze–thaw mechanisms, where the former agent is considered to be of particular importance where the platforms are most levelled. A bulge on the outermost part of the shoreline features is described for the first time and interpreted as a consequence of freeze-on plucking. Mean platform widths range from 9–29 m, while mean cliff degradation is estimated to be 140 m3 m− 1. By adapting the age span of Main Line formation reported elsewhere, maximum erosion rates over 1 Ma totals to 58 km. The study sheds light on the Main Line's potential as a reference level when assessing postglacial landscape development and highlights the significance of episodic erosional events in cold climate regimes.

Landscape development and deglaciation history of fjord-valley deposits in Buvika, Mid Norway[Deglaciation history and landscape development of fjord-valley deposits in Buvika, Mid-Norway]

Thick fine-grained, nonuniformly stratified deposits along a 20 km stretch coastline have been investigated using a combined marine and terrestrial approach. The sediments were deposited rapidly in glaciomarine, marine and submarine ice-contact environments during the Allerod and Younger Dryas periods. Rapid glacioisostatic rebound caused extensive modification of the landscape, mainly by sliding. Slides in the area were affected by the bedrock morphology, location and sedimentation rate of the glaciomarine sediments, isostatic rebound, presence of gas/fluids in marine sediments and later, river incision, tides and groundwater flow. Spatial and temporal distribution of slide deposits in the marine stratigraphy, and morphology of submarine and terrestrial features give detailed information of landscape evolution through time. This is illustrated by conceptual profiles from three areas that explain the landscape evolution and changing processes during the rebound. The most intensive slide activity, both in frequencies and volumes, and hence the most considerable landscape modification occurred early in the Holocene period i.e. when the relative sea level fell most rapidly.

Many bedrock-confined fjord valleys along the Norwegian coast contain thick accumulations of fine-grained sediments that were deposited during and after the last deglaciation. The deposits gradually emerged above sea level due to glacioisostatic uplift, and fjord marine sedimentation was gradually followed by shallow marine and fluvial processes. During emergence terraces and river-cut slopes were formed in the valleys. Subsequent leaching of salt ions from the pore water in the marine deposits by groundwater has led to the development of quick clay. The deposits are subject to river erosion and destructive landslides involving quick clay. Most slides are of prehistoric age. Others are known from modern observations as well as from historic records. Landforms such as distinct slide scars or the hummocky terrain of slide deposits may be strongly modified by secondary processes. In addition, deposits from the most liquid part of quick clay slides may have planar surfaces. Clay-slide deposits on a fluvial or deltaic terrace, therefore, are not always easily recognized from morphology, and only exposures may reveal their internal structures and allow them to be distinguished from overbank flood sediments. Detailed sedimentological work shows that slide deposits in such setting consist of distinct facies containing reworked marine sediments. We propose three facies successions of clay-slide deposits that form a continuum. The dominant components of these succession types are: slightly deformed blocks of laminated clay and silt (A), highly deformed clay and silt with gravel clasts (B) and massive to stratified clay and silt with scattered clasts (C). We suggest that in many cases a basal muddy diamicton is a characteristic, and possibly diagnostic feature. Processes and depositional models are interpreted from the different succession types. The results may be relevant for identifying clay-slide deposits elsewhere and may be useful during general mapping of fjord marine deposits and characterization of slide-prone areas as well as during identification of prehistoric slides.

The onshore record of Middle to Late Weichselian sediments and glacial history in Norway indicates a succession of four major ice advances alternating with rapid, considerable ice recessions and interstadial conditions. During all the glacial advances the ice sheet expanded from onshore/inland positions to the shelf areas. The basis for visualizing these variations in glaciation curves constructed along nine transects from inland to shelf, and for interpretation of the palaeoclimatic history, is the regional Quaternary stratigraphy, more than 300 datings, fossil content and some palaeomagnetic data. The methods applied in recent years for AMS radiocarbon dating of glacial sediments with low organic carbon content have given promising results with respect to accuracy and precision, and the results of such datings were an important tool for our reconstructions and for timing of the ice oscillations. The rapid and rhythmic ice fluctuations, as reconstructed in our new model, have been fairly synchronous in most parts of Norway. Ice advances commenced and culminated at 40, 30-28, 24-21 and 18-15 (14C) Kya. We describe three intervening interstadials from inland sites: Hattfjelldal I, Hattfjelldal II and Trofors. Our stratigraphical record also includes many indications of high, pre-Holocene, relative sea levels, suggesting a considerable glacioisostatic depression of western Scandinavia during the interstadials. In our glaciation model we suggest that, in addition to precipitation, the mountainous fjord and valley topography, glacial isostasy and relative sea level changes were probably more important for the size of the glacial fluctuations than were air temperature changes.

For decades, mapping of Quaternary geology in Norway has been an important basis for hazard and risk assessment for landslides in highly sensitive clay (quick clay). One aspect of particular significance is information on the occurrence of fine-grained, marine deposits including clays. The marine limit (ML) defines a natural upper limit to these deposits, so issues concerning marine clays can be disregarded above ML. Below ML, a filtering of the Quaternary map information is needed to identify areas where clays are potentially present. Fine-grained, marine deposits are more frequently encountered below some deposit types than others, and the possibility of encountering marine clays within an area is defined as clay-deposit susceptibility. Stratigraphic information is needed for verification. Further landslide susceptibility assessment requires additional information on topography and ground conditions. Other geological information is also important such as on the distribution of landslide debris and landslide scars. Here, it is beneficial to use high-resolution, digital elevation models for detailed analysis of the terrain also below sea level in near-shore areas. Maps with filtered geological information can work as a supplement to maps produced during the ongoing quick-clay mapping program and as a help prioritize areas requiring further investigation.