The potential of sedimentology and stratigraphy in avalanche-hazard research

Detailed sedimentology studies in cross sections and studies of recent processes on avalanche-dominated colluvial fans have been combined in order to evaluate the characteristic sedimentary facies of avalanche processes. These include rock avalanches, rockfalls, debrisflows and snow avalanches. Moreover, the sedimentary facies provides important data on the mechanics of the depositional processes involved. Avalanche deposits are commonly separated by soil or peat beds, which can be dated by the radiocarbon method. In many cases it is thus in many cases possible to estimate the frequency of different avalanche events through time. Geological data can also be used in combination with other methods to evaluate potential impact or run-out zones. Debrisflow and snowflow events can be recognised in excavations, and the run-out distances for older events can thus be mapped. Snow avalanches commonly transport considerable amounts of debris, and far-reaching snow avalanches can be recognised from the occurrence of scattered clasts in peat or soil successions. Such data can be important in testing statistical and dynamic run-out models. A register of historic and prehistoric rock avalanches is currently being compiled, a database which will be of fundamental importance in the future in evaluating run-out distance for potential bedrock failures. This research as a whole suggests that detailed geological studies involving sedimentology and stratigraphy can be of interest and importance in projects concerned with avalanche hazard

Rock-avalanche hazard in Møre & Romsdal, western Norway

Flood waves generated by large rock avalanches have caused major disasters in Norway. Many of these events are restricted to a relatively limited zone in the counties Møre & Romsdal and Sogn & Fjordane. Geological studies confirm that this zone has been affected by large-scale rock avalanches throughout the postglacial period. The number of rock-avalanche events is much higher than expected, and many of them are from the latest part of the postglacial period (the last 5000 years), thus in contrast to the general assumption that most of these events occurred shortly after the deglaciation. Rock avalanches and related flood waves often represent a higher risk than other types of avalanches in the region, due to the potential of causing extensive damage. It can be concluded that the avalanche probability limit of 10-3 pr. annum which is used for normal buildings in Norway, is not applicable for rock-avalanche hazard. The study indicates that rock-avalanche hazard should be taken into account in several inhabited areas. More work needs to be done in order to produce hazard-zone maps

Hazards, Climate Change and Extreme Weather Events

Geohazards are events related to geological features and processes that cause loss of life and severe damage to property and the natural and built environment. The most common and destructive geohazards in Norway are snow avalanches, clay-, debris- and rock slides, and floods, which together caused more than 2000 deaths during the last 150 years. Statistically, about 10 large slides and avalanches are expected to occur in Norway the next 50-100 years, each with possibly 20-100 deaths, unless preventive planning and actions are made. In addition to the loss of lives, geohazards pose a large impact on infrastructure and the daily life in many parts of Norway. A possible increase of extreme weather events in the next 50 years may lead to change in the type and frequency of slides and avalanches. The main objective of the four year research project GeoExtreme is therefore to assess the geohazard situation in Norway in a changing climate over the next 50 years. The initial step is a statistical analysis of the relationships between meteorological conditions and geohazards. To do this, a national database of slide events has been established. The time and location of these events will be compared to interpolated meteorological datasets for the last 100 years. Results of this analysis will be used in combination with climate scenarios for the next 50 years to produce a picture of possible future geohazards in Norway. The effects on the local society are studied in detail in four study areas representing different climate areas in Norway. An important part of the project is the assessment of socioeconomic consequences of geohazards in Norway, both in the past, and in the future, under the predicted climate scenarios. Important parameters here are cost related to damage by natural disasters as well as to mitigation measures, ability to learn by experience, changes in preparedness, and impact on policy makers. The first results show a high predictability of slide events by standard meteorological observations. Also the vulnerability pattern shows significant changes from hazard for residential areas to transport lines and leisure time activities. The presentation gives a general overview over the project and presents some of the first results of the analyses

Veslemannen høsten 2014

Dette er en rapport som er utarbeidet innenfor NIFS samarbeidet. Den gir en oppsummering og kort evaluering av håndteringen av hendelsen ved Mannen i forbindelse med at et mindre fjellparti viste store bevegelser høsten 201

Relating 3D surface displacement from satellite- and ground-based InSAR to structures and geomorphology of the Jettan rockslide, northern Norway

This study combines remote sensing data from ground- and satellite-based radar to calculate 3D displacement vectors for the Jettan rockslide, Troms, northern Norway. Using 3D displacement vectors, aspect data and strain rates in conjunction with structure (foliation, faults, fractures), geomorphological elements (ridges, scarps, terraces, depressions), topography and borehole data, we identify zones undergoing displacement, e.g., extension and compression, displacement into- or out-of-the-slope and/or various degrees of tilting. Our results show variable 3D displacement velocities, from north to south, that segment the rockslide into distinct domains. Displacement patterns are structurally controlled, as spatial variation in azimuth and plunge of 3D displacement vectors can be related to variation in attitudes of the host-rock foliation, faults and fractures. In the north, a complex graben system surrounded by orthogonal NW–SE and NE–SW-trending geomorphological elements, shows a repeated stepping 3D displacement pattern. This may indicate a complex fault geometry at depth, including stepped and discontinuous slide surfaces. We interpret 3D displacement into-the-slope in the upper part, and out-of-the-slope in the lower part, to be back-rotation of antithetic blocks with planar fractures becoming curved/listric gliding surfaces with depth. Downslope reduction in velocity indicates compression and stacking of blocks. In the southern area, N–S-trending geomorphological elements are arranged parallel to the hillslope. 3D displacement vectors show a more homogenous displacement pattern indicating movement along planar, hillslope-parallel, fracture sets at depth. We propose a structuralcontrolled slope displacement model including alternate planar- and wedge-failure, in addition to displacement along planar and listric fractures merging into foliation at depth. Using the Jettan rockslide as a case study, we show how remote sensing data may aid examination of structural and topographic controls on rockslide kinematics, thus giving new insights into subsurface geometry

Evidence of rock slope breathing using ground-based InSAR

Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR) campaigns were performed in summer 2011 and 2012 in the Romsdalen valley (Møre & Romsdal county, western Norway) in order to assess displacements on Mannen/Børa rock slope. Located 1 km northwest, a second GB-InSAR system continuously monitors the large Mannen rockslide. The availability of two GB-InSAR positions creates a wide coverage of the rock slope, including a slight dataset overlap valuable for validation. A phenomenon of rock slope breathing is detected in a remote and hard-to-access area in mid-slope. Millimetric upward displacements are recorded in August 2011. Analysis of 2012 GB-InSAR campaign, combined with the large dataset from the continuous station, shows that the slope is affected by inflation/deflation phenomenon between 5 and 10 mm along the line-of-sight. The pattern is not homogenous in time and inversions of movement have a seasonal recurrence. These seasonal changes are confirmed by satellite InSAR observations and can possibly be caused by hydrogeological variations. In addition, combination of GB-InSAR results, in situ measurements and satellite InSAR analyses contributes to a better overview of movement distribution over the whole area

Kinematic and morphological inventories of slope movement in Northern Norway

We developed simplified ground velocity products based on Interferometric Synthetic Aperture Radar (InSAR) to inventory slope movements in a ca 7500 km2 region in Northern Norway. We used a multiple temporal baseline InSAR stacking procedure based on 2015–2019 ascending and descending snow-free Sentinel-1 images to take advantage of a large set of interferograms and exploit different detection capabilities. Moving areas were identified, classified according to six velocity brackets, and morphologically associated to six landform types (rock glaciers, rockslides, glaciers/moraines, talus/scree deposits, solifluction/cryoturbation and composite landforms). We updated the pre-existing inventories of rock glaciers and rockslides in the region using InSAR kinematics. Landform delineations and divisions were refined, and newly detected landforms (54 rock glaciers and 20 rockslides) incorporated into the databases. The updated inventories consist of 414 rock glacier units within 340 single- or multi-unit(s) systems and 117 rockslides. Based on InSAR, a kinematic attribute assigned to each inventoried landform documents the magnitude order of the movement