Extreme precipitation induced landslide event on 30 July 2019 in Jølster, western Norway

A torrential rain event struck western Norway on Tuesday 30 July 2019. Most severely affected was the Jølster community, where numerous landslides and floods damaged public infrastructure and private property. This resulted in one fatality, 150 people evacuated from the area and the closure of Highway E39, the main coastal transport route in Norway. Weather radar data reveal large spatial and temporal variations in rainfall intensity and areas with highest intensities correspond to observed shallow landslide clusters where the 200-year rainfall event magnitude was clearly exceeded. The majority of 120 shallow landslide source areas share common characteristics: they are situated above or at the tree line, in thin to very thin soil, in contact with the bedrock or large boulders and in rather steep terrain (>30 degrees). Several lines of evidence suggest that soil in the source areas was not fully saturated, but instead failed due to locally high porewater pressures as short and intense rainfall on dry ground led to water infiltration through open cracks in the surface cover, and commonly at soil-bedrock or soil-boulder contacts. The most far-reaching debris flows of the event have steep upper transport areas, in places with cliff sections, which created sufficient flow-momentum despite small starting volumes. We note that erosion along the flow path was relatively superficial since incomplete soil saturation with depth likely prevented deeper entrainment. Consequently, water-to-solid ratios in the mobilised material was high and the runout possibly longer but less destructive compared to more deep-seated landslide events. This type of summer torrential rain on unsaturated soil require adjustments to how Norwegian society predicts and prepares for shallow landslides triggered during these events, compared with landslides following longer-lasting rainfall.publishedVersio

Extreme precipitation on dry ground in western Norway – characteristics of induced landslides call for adaptation of the Norwegian practice in landuse planning

Following a particularly dry summer, a torrential rain event struck Western Norway on Tuesday 30 July 2019. The resulting floods and shallow landslides caused one fatality and severe damages to public and private infrastructure in the former Jølster municipality. Building on earlier work, in which we identified characteristics of the shallow landslides induced by torrential rains on unsaturated soils, we here present suggestions for adaptation of the Norwegian practice in landuse planning.publishedVersio

Extreme precipitation on dry ground in western Norway – characteristics of induced landslides call for adaptation of the Norwegian practice in landuse planning

Following a particularly dry summer, a torrential rain event struck Western Norway on Tuesday 30 July 2019. The resulting floods and shallow landslides caused one fatality and severe damages to public and private infrastructure in the former Jølster municipality. Building on earlier work, in which we identified characteristics of the shallow landslides induced by torrential rains on unsaturated soils, we here present suggestions for adaptation of the Norwegian practice in landuse planning

Rapid post-glacial bedrock weathering in coastal Norway

Quantifying bedrock weathering rates under diverse climate conditions is essential to understanding timescales of landscape evolution. Yet, weathering rates are often difficult to constrain, and associating a weathered landform to a specific formative environment can be complicated by overprinting of successive processes and temporally varying climate. In this study, we investigate three sites between 59°N and 69°N along the Norwegian coast that display grussic saprolite, tafoni, and linear weathering grooves on diverse lithologies. These weathering phenomena have been invoked as examples of geomorphic archives predating Quaternary glaciations and consequently as indicators of minimal glacial erosion. Here we apply cosmogenic nuclide chronometry to assess the recent erosional history. Our results demonstrate that all three sites experienced sufficient erosion to remove most cosmogenic nuclides formed prior to the Last Glacial Maximum. This finding is inconsistent with preservation of surficial (<1–2 m) weathered landforms under non-erosive ice during the last glacial period, while simultaneously demonstrating that post-glacial weathering and erosion rates can be locally rapid (4–10 cm kyr−1) in cold temperate to subarctic coastal locations

Alpine lake sediment archives and catchment geomorphology : causal relationships and implications for paleoenvironmental reconstructions

Lake sediments are frequently used as archives of climate and environmental change. Minerogenic sediment variability in alpine lakes is often used to reconstruct past glacier and slope process activity. Alpine lake sediments can however have many different origins, which may induce errors in paleoenvironmental reconstructions. The aim of this project was to enhance the understanding of minerogenic lake sedimentation in alpine lakes and improve their use as environmental archives. Catchment geomorphology and Holocene sediment sequences were analysed for five alpine lakes. Several minerogenic sediment sources were detected in catchments and sediment sequences. Slope-, fluvial-, periglacial-, nival- and aeolian sediment transportation processes contribute to create complex lake sediment patterns. Large variations in sedimentation rates were discovered within and between lakes, which has implications for sampling strategies and age-model constructions. Similar fine-grained minerogenic laminations were found in four of the investigated lakes, despite large differences in setting. The demonstrated similarity between glacial and non-glacial lakes may complicate interpretations of glaciolacustrine sediment signals. The main conclusion is that lake sedimentation in alpine environments is highly dependent on several geomorphological factors. All lakes should therefore be viewed as unique and the geomorphology should be thoroughly investigated before environmental reconstructions are based on lake sediment proxies. This study has confirmed the multi-source origin of alpine lake sediment, which also opens possibilities of more multi-faceted paleoenvironmental studies. Different process-proxies could potentially be used to separate different climate signals, e.g. precipitation, temperature and wind, in lake sediments. Analysis of grain-size distribution, detailed mineralogy and magnetic mineralogy in combination with X-ray radiography are suggested methods for such reconstructions

Extreme precipitation on dry ground in western Norway – characteristics of induced landslides call for adaptation of the Norwegian practice in landuse planning

Following a particularly dry summer, a torrential rain event struck Western Norway on Tuesday 30 July 2019. The resulting floods and shallow landslides caused one fatality and severe damages to public and private infrastructure in the former Jølster municipality. Building on earlier work, in which we identified characteristics of the shallow landslides induced by torrential rains on unsaturated soils, we here present suggestions for adaptation of the Norwegian practice in landuse planning

Thaw slump inventory of Nordenskiöld Land (Svalbard Archipelago)

We present a comprehensive inventory of thaw slumps (landslides developed in the Arctic and sub-Arctic areas) in Nordenskiöld Land (Svalbard Archipelago). We used the most recent orthophotos (5 x 5 m pixel size) acquired in 2009-2011 from the Web Map Services (WMS) of the Norwegian Polar Institute. The thaw slumps were identified and digitised on-screen as polygons in the WGS_1984_UTM_Zone_33N coordinate reference system. We identified a number of 562 thaw slumps, that will be used along with the thermo-erosion gullies inventory to provide the first multi-hazard predictive model in the Arctic

Thermo-erosion gullies inventory of Nordenskiöld Land (Svalbard Archipelago)

We present a comprehensive inventory of thermo-erosion gullies (gullies developed in the Arctic and sub-Arctic areas) in Nordenskiöld Land (Svalbard Archipelago). We used the most recent orthophotos (5 x 5 m pixel size) acquired in 2009-2011 from the Web Map Services (WMS) of the Norwegian Polar Institute. The thermo-erosion gullies were identified and digitised on-screen as polygons in the WGS_1984_UTM_Zone_33N coordinate reference system. We identified a number of 908 thermo-erosion gullies, that will be used along with the thaw slumps inventory to provide the first multi-hazard predictive model in the Arctic

Coastal Erosion of Arctic Cultural Heritage in Danger: A Case Study from Svalbard, Norway

Strong cultural heritage management relies on a thorough evaluation of the threats faced by heritage sites, both in the present and in the future. In this study, we analysed the changes in the position of Hiorthhamn shoreline (Svalbard), which is affecting coastal cultural heritage sites, for a period of 93 years (1927–2020). Shoreline changes were mapped by using maps, ortophotos, drone images, terrestrial laser scanning (TLS), and topographic surveys. Also, TLS was used to 3D document the endangered coastal cultural heritage sites. Detailed sedimentological and morphological mapping was made in the field and from the newly acquired drone images in order to understand shoreline-landscape interaction and to depict changes occurring from 2019 to 2020. Short-term (2019–2020) and long-term (1927–2020) shoreline erosion/accretion was made with the help of the Digital Shoreline Analysis System (DSAS) and prompted a subdivision of three sectors, based on change pattern. Compared to a previous long-term analysis (1927–2019), this year’s average erosion rate analysis (expressed by the EPR parameter) for the 93-year period is −0.14 m/yr. This shift in mean development is due to a newly formed spit-bar in Sector 2. Referring strictly to Sector 1, where the protected cultural heritage objects are located, the erosion rate increased from the previous analysis of –0.76 m/yr to −0.77 m/yr. The shoreline forecast analysis highlights that half of the protected cultural heritage objects will likely disappear over the next decade and almost all the cultural heritage objects analysed in this study will disappear in roughly two decades. This shows the great danger the Arctic’s cultural heritage sites is in if no mitigation measures are undertaken by the local authorities