Stratigraphy and age of a Neoglacial sedimentary succession of proglacial outwash and an alluvial fan in Langedalen, Veitastrond, western Norway

This study presents the sedimentary succession of an outwash plain and an alluvial fan located along the valley Langedalen at the south-eastern side of the Jostedalsbreen ice cap in inner Sogn, western Norway. A newly exposed ~2.8-m-high section along the southern riverbank of Langedøla river shows alternating layers of minerogenic sediments and peat layers with tree logs, identified as Salix sp. The section is situated in the distal part of an alluvial fan built out from the southern slope of Langedalen. Six AMS radiocarbon dates of tree fragments indicate that the accumulation of the fine-grained sediments in the lower part of the section was initiated earlier than the basal radiocarbon date of 914–976 calibrated years CE (1σ age range). These basal, fine-grained sediments are interpreted as proglacial outwash deposited in a floodplain depression or abandoned river channel in a low-energy glaciofluvial environment. Periods of low glacier cover, low river discharge or low-water stands over the floodplain allowed peat formation and the growth of trees and shrubs in the valley. The radiocarbon dates further indicate relatively rapid sediment accretion (~2.7–3 cm a−1) between 190 and 125 cm below the sediment surface, equivalent to approximately 1220 to 1250 cal. a CE (1σ age range). At ~60 cm depth below the surface, dated to approximately 1590 to 1620 cal. a CE (1σ age range), a transition to more coarse-grained, sandy and gravelly sediments indicates increased sediment supply and distal expansion of the alluvial fan. This occurred most likely as a consequence of increased sediment yield from expanding glaciers along the southern valley side of Langedalen as a response to the initial Little Ice Age glacier growth. Based on these results, the accretion and progradation of glacier-fed alluvial fans mainly occur during periods of glacier advance rather than during glacier recession.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

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

Evolution of a high-latitude sediment drift inside a glacially-carved trough based on high-resolution seismic stratigraphy (Kveithola, NW Barents Sea)

Published version, source at http://doi.org/10.1016/j.quascirev.2016.02.007. License CC BY-NC-ND 4.0.Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea, an epicontinental shelf sea of the Arctic Ocean located off northern Norway and Russia. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. In general, drift deposits are commonly characterized by high lateral continuity, restricted occurrence of hiatuses and relatively high accumulation rates, and thus represent excellent repositories of paleo-environmental information. We provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift, which is further supported by some preliminary lithological and sedimentological analyses. The complex morphology of the drift, imaged by combining all available multibeam data, includes a main and a minor drift body, two drift lenses in the outer part of the trough, more or less connected drift patches in the innermost part and small perched sediment patches in a structurally-controlled channel to the north. The seismic (PARASOUND) data show that the main and minor drift bodies are mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting the occurrence of more energetic sedimentary conditions. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics, along with the morphological and seismic information, suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Though both Atlantic and Arctic waters are known to enter the trough, from the west and the north respectively, brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western Barents Shelf since that time. The units inferred to have been deposited under more energetic sedimentary conditions (tentatively dated to the Younger Dryas and to 8.9–8.2 cal ka BP) are suggestive of stronger BSW formation. In general, we infer that variations in the bottom current regime were mainly related to BSW formation due to atmospheric changes. They could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited, later open shelf current, which progressively established on the western Barents Sea shelf

Skredfarevurdering for tomt 57/27 i indre Haugsdal, Masfjorden kommune

Det ble gjennomført ei skredfarevurdering for ei tomt eid av Thomas Løvik i indre Haugsdal med gards- og bruksnummer 57/27. Dimensjonerende skredtype er steinsprang. Steinsprang fra pallstokkhatten er vurdert til å ha utløp med størst årlig nominell sannsynlighet 1/5000 over store deler av tomten i nord, mens steinsprang fra de lokale skrentene har kort rekkevidde og berører kun mindre deler av tomten. Planlagt fritidsbolig kan oppføres i det flate partiet av tomt 57/27 slik at det ligger innenfor en faresone der årlig nominell sannsynlighet for skred er mindre enn 1/1000 og vil dermed tilfredsstille kravene for oppføring av byggverk under sikkerhetsklasse S2 for skred i TEK17

Palaeoenvironment of the Barents Sea during the last deglaciation and Holocene : processes and timing

The scope of this PhD thesis is twofold: Firstly, processes, patterns and timing of the last deglaciation in the Barents Sea are reconstructed and secondly, depositional conditions on the Barents shelf during Holocene are elucidated. This cumulative PhD thesis encompasses an introductory part and five papers - three as first-author and two as co-author. Three papers are focused on the most prominent geomorphological freature of the western Barents shelf, 850 km long cross-shelf trough Bjørnøyrenna (The Bear Island Trough). One detailed study examines processes and timing of the first step of glacial retreat in outer Bjørnøyrenna and establishes a minimum age of 17 cal ka for initial deglaciation. A second study focuses on a grounding line system in uppermost Bjørnøyrenna, witnessing a surge-type readvance towards the final collapse of the marine-based Barents Sea Ice Sheet. A third study focuses on contrasting ice stream flow regimes and processes observed from glacial maximum over initial deglaciation towards final deglaciation. Two additional studies are located in the relatively small formerly glaciated trough Kveithola, north-west of Bjørnøya (Bear Island). The first focuses on the most recent deglaciation history and establishes an indirect deglaciation age for Spitsbergenbanken 14.2-13.9 cal ka ago. The other reconstructs the complex glacial retreat through Kveithola and associated processes based on geophysical data. As a whole, this PhD thesis improves existing chronology during deglaciation and Holocene for the Barents Sea, advances existing depositional models of ice-marginal and deglacial processes as well as it adds to established conceptional models of glacial retreat. While presented Holocene data is less conclusive, it might create the awareness that the large Storegga tsunami at 8.2 cal ka may have had an erosional impact on shelf sediments and thereby motivate further research

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

Grounding line proximal sediment characteristics at a marine-based, late-stage ice stream margin

Geomorphological evidence suggests that ice streams undergo frequent dynamic changes towards the end of their life cycles, but the associated sedimentary characteristics and processes remain poorly understood. Here, we present new sedimentological data from a Late Weichselian marine‐based ice stream in upper Bjørnøyrenna, northern Barents Sea, which experienced accelerated flow, intense calving of large icebergs, ice stream stagnation, ice shelf formation and disintegration. Observed till characteristics support the idea of spatially and temporally variable basal drag underneath ice streams. In addition, fast flow may have been accommodated in dilatant deforming till as well as through basal sliding over sticky spots of stiffer till. The grounding zone is shown to be highly transient and spatially variable during the final ice stream readvances, thus making the categories subglacial/proglacial of little value. In line with previous radiocarbon dates, we find that uppermost Bjørnøyrenna was deglaciated before ∼11.3–12.0k cal a BP. Finally, the provenances for the latest ice stream advance and an older ice flow event are inferred based on a novel way of using element geochemistry, helping define ice dome configuration in the northern Barents Sea

Grounding line proximal sediment characteristics at a marine-based, late-stage ice stream margin

This is the peer reviewed version of the following article: Rüther, D.C., Winsborrow, M., Andreassen, K. & Forwick, M. (2017). Grounding line proximal sediment characteristics at a marine-based, late-stage ice stream margin. Journal of Quaternary Science, 32(4), 463-474. https://doi.org/10.1002/jqs.2939, which has been published in final form at https://doi.org/10.1002/jqs.2939. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Geomorphological evidence suggests that ice streams undergo frequent dynamic changes towards the end of their life cycles, but the associated sedimentary characteristics and processes remain poorly understood. Here, we present new sedimentological data from a Late Weichselian marine‐based ice stream in upper Bjørnøyrenna, northern Barents Sea, which experienced accelerated flow, intense calving of large icebergs, ice stream stagnation, ice shelf formation and disintegration. Observed till characteristics support the idea of spatially and temporally variable basal drag underneath ice streams. In addition, fast flow may have been accommodated in dilatant deforming till as well as through basal sliding over sticky spots of stiffer till. The grounding zone is shown to be highly transient and spatially variable during the final ice stream readvances, thus making the categories subglacial/proglacial of little value. In line with previous radiocarbon dates, we find that uppermost Bjørnøyrenna was deglaciated before ∼11.3–12.0k cal a BP. Finally, the provenances for the latest ice stream advance and an older ice flow event are inferred based on a novel way of using element geochemistry, helping define ice dome configuration in the northern Barents Sea