Ivar Berthling

Aspects and concepts on the geomorphological significance of Holocene permafrost in southern Norway

This review paper aims at discussing aspects and concepts of the significance of the spatial and temporal distribution of permafrost on glacial and gravitational processes in southern Norway. The study first reviews the distribution of mountain permafrost in southern Norway in comparison with high-relief alpine areas like the Alps, and then discusses the influence of permafrost on gravitational and glacial–geomorphological processes. The basis for the paper is a regional-scale distribution model of mountain permafrost in southern Norway, which is analysed in relation to topographic variations within the same area. The model allows a crude extrapolation to past and future permafrost distribution, which is discussed in relation to geomorphic processes.

Integrated vulnerability mapping for wards in Mid-Norway

The future climate of Norway is expected to become “warmer, wetter, and wilder”, and it is anticipated that this will cause more extreme weather events. Local authorities therefore need to increase their ability to assess weather-related hazards such as flooding and landslide, as well as peoples’ capacities to cope with such events. Any evaluation of future vulnerability towards natural hazards should use todays situation as the baseline. In this article, we present this baseline: a vulnerability assessment for the present. Our vulnerability assessment incorporates both physical and social dimensions of vulnerability and screens Mid-Norway at the lowest administrative level. The results reveal a considerable geographic variation regarding vulnerability. The assessment identifies the most vulnerable localities within a municipality and could thus be relevant for the local authorities. By incorporating knowledge held by the local authorities, the vulnerability mapping could be made even more relevant.

HOLOCENE ROCKWALL RETREAT AND THE ESTIMATION OF ROCK GLACIER AGE, PRINS KARLS FORLAND, SVALBARD

Abstract. This paper presents a simple analytical model for estimating rock glacier age by coupling the ratio of frontal advance to total rock glacier length and the ratio of debris volume in the rock glacier to present debris flux in the talus cone–rock glacier transition zone. The model was applied to two rock glaciers at Prins Karls Forland, Svalbard. By assuming volumetric debris contents in the deforming layer of the rock glacier of between 0.3 and 0.4, we obtained age estimates for the rock glaciers of between 12 ka and 24 ka. The corresponding average rockwall retreat rates are between 0.30 and 0.62 mm a‐1. Considering the limitations of the model, we suggest a minimum age of 13 ka for the initiation of rock glacier development. Using this age, rockwall retreat rates for the seven rock glaciers investigated at Prins Karls Forland are between 0.13 and 0.64 m ka‐1 (assuming the volumetric debris content for the whole rock glacier/talus cone is 0.35). The model requires further testing on other datasets, better field estimates of the debris content and depth of the deforming layer, and could also benefit from the inclusion of an unsteady debris supply function in order to refine age estimates.

Topographic radiation balance models: Sensitivity and application in periglacial geomorphology

Direct solar radiation integrated over one year is a function of latitude and time of year, and topographic slope , aspect and shadowing control the local distribution. Recently, several spatial models have been developed which estimate the radiation balance based on digital elevation models, taking into account aspect, slope and shadowing effects. For the periglacial realm, these models are integrated both in models estimating possible occurrence of mountain permafrost and in studies of active layer dynamics. In this article our aim is to assess and discuss sensitivity and validations of the radiation balance model SRAD, in comparison with two other topographic-based radiation models. The study site and field data are from Finse, Southern Norway.

Subrecent sediment dynamics and sediment budget of the braided sandur system at Sandane, Erdalen (Nordfjord, Western Norway)

A study was carried out of the subrecent sediment budget of a braided sandur system in a U-shaped valley linked to the Jostedalsbreen ice field in Nordfjord, in Western Norway. Special focus was on (i) the detection of different zones with negative, positive or balanced subrecent (following the Little Ice Age advance) sediment budget within the braided sandur system, (ii) the identification of sediment sources upstream of Sandane and from the slope systems to both sides of the braided sandur system, and (iii) the analysis of the subrecent sediment budget of the entire Sandane system. A combination of methods was applied in the analysis. The upstream part of Sandane was found to be characterised by a negative subrecent sediment balance, with erosion of coarse sediments from the Little Ice Age advance. In comparison, the downstream parts of Sandane have a balanced to slightly positive subrecent sediment budget, with formation of younger flood sediments and more stable channels. Thus, the subrecent sediment budget of Sandane appears to be slightly negative. Present-day coupling of slope and fluvial systems is limited and only a rather small amount of sediments is directly transported from the slopes into the braided sandur. In sum, fluvial sediment transport following the Little Ice Age period appears to be supply-limited.

Bed load transport in a steep snowmelt-dominated mountain stream as inferred from impact sensors

The article reports results from bed load transport investigations using impact sensors in Vinstra, a steep snowmelt-dominated mountain stream in Central Norway. The impact sensors proved able to detect thresholds for bed load entrainment. With increasing discharges surpassing the threshold for entrainment, both the magnitude and variance in impact force increases, but also showing differing rating relationships on rising and falling flows. Substantial bed load transport was only observed during the snowmelt-dominated spring flood period and impact magnitude was observed on average to follow diurnal variations in discharge during the spring flood event, but with a clockwise hysteresis relationship.

Sediment fluxes from creep processes at Jomfrunut, southern Norway

Based on velocity measurements of surface and subsurface creep, sediment flux due to solifluction and ploughing boulder activity were estimated in a mid-alpine site in southern Norway (Finse, UTM185198). The results indicate geomorphic work performed by solifluction of approximately 9 MJkm -2 a -1 and imply that sediment flux rates by solifluction under favourable conditions may be comparable to or exceed those of rapid mass movement obtained in more alpine environments.

Continuous measurements of solifluction using carrier-phase differential GPS

In this research note, we test the potential of differential carrier-phase GPS measurements (DGPS) for continuous recording of the slow mass wasting occurring in solifluction. DGPS is shown to be capable of yielding records of high temporal resolution and accuracy.

Downslope Displacement Rates of Ploughing Boulders in A Mid-Alpine Environment: Finse, Southern Norway.

Annual and seasonal displacements of ploughing boulders were investigated at Finse, southern Norway, by traditional surveying and differential carrier‐phase global positioning system measurements. Annual displacement rates were mainly below 10 mm/year, although one particular season showed rates of 26 mm/year on average. There was a tendency for larger boulders to travel faster. Seasonal displacements were restricted to the annual freeze‐thaw cycle. The frost heave seems to have a significant horizontal component, which does not necessarily point in the downslope direction. Thus, the concept of frost creep is not applicable to the investigated ploughing boulders. On the other hand, due to tilting of the boulders, a momentum may be gained during thaw consolidation that could induce downslope displacements. Such a process will work together with gelifluction.

The drainage history of glacial lake Nedre Gl msj, southern Central Norway

During the last deglaciation of southern Norway, a glacial lake (Nedre Glamsjo) was dammed between the remnants of the continental ice sheet and the lowest pass on the main watershed towards Trondelag. When the lake was drained subglacially, some of the water had to flow across a valley divide to escape, and during this event a huge canyon (Jutulhogget) was cut down into the bedrock. The details of this drainage have not been resolved. The main question concerns whether the lake was drained once and for all, or whether the drainage channel through the ice closed so that several jokulhlaups were possible. In this paper, we propose a conceptual model for the event based on the geomorphological record of shorelines, terraces, and flood erosional and depositional features within the lake basin. We suggest that Nedre Glamsjo was drained periodically, each event cutting the canyon Jutulhogget further down.