Halvor Bunkholt

Systematic Mapping of Large Unstable Rock Slopes in Norway

Historically, large rock slope failures impacting into a fjord and causing a several tens of metre high displacement wave have been one of the natural hazards in Norway claiming most lives. In the last 7 years, the Geological Survey of Norway has implemented a systematic mapping approach to characterize unstable rock slopes prone to catastrophic failures, so that future events can be recognized beforehand and society can adapt to the hazard. Systematic mapping has been carried out in three countries and more than 285 unstable slopes have been found. Of these sites, 62 are monitored periodically and 4 have been characterized as high risk objects with continuous monitoring systems installed. In order to classify the likelihood of a future event, rock slope mapping of each object includes the analyses of slide kinematic, velocity of the slide accompanied with other indicators of slide activity and an analysis of recurrence of previous events along the slope.

Hazard and Risk Classification for Large Unstable Rock Slopes in Norway

We present a classification system for hazard and risk that is posed by unstable rock slopes in Norway that might undergo catastrophic failure in future and can cause loss of life. The system is scenario-based as the intensity and rate of displacement, as well as the geological structures activated by the sliding rock mass vary significantly on the slopes. In addition, for each scenario the secondary effects, such as genera- tion of displacement waves or landslide damming of valleys with the potential of later outburst floods, are evaluated. The hazard analysis is based on two types of criteria: 1) Structural site investigations including analysis of the development of a back-scarp, lateral boundaries and basal sliding surface. This includes a kinematic analysis for sliding and toppling based on slope orientation, persistence of main structures and morphologic expressions of the sliding surface. 2) Analysis of slope activity primarily based on slide velocity, change of deformation rates, observation of rockfall activity, and historic or prehistoric events. The analysis of consequences focuses on the potential fatalities to the rock slide scenarios and secondary ef- fects. Based on the hazard and consequence analysis each scenario is classified in a risk matrix into cat - egory low, medium or high risk.

Use of Satellite and Ground Based InSAR in Hazard Classification of Unstable Rock Slopes

A newly developed hazard classification system for large unstable rock slopes depends on the evaluation of a number of criteria. These criteria include both displacement rates and the structural development of the unstable slope. Satellite and ground-based interferometric radars have the potential to measure the displacement of active rockslides. By using several complimentary InSAR datasets, with different viewing geometries, we are able to assess both movement criteria and a number of criteria related to structural development of the bounding surfaces.

Database of Unstable Rock Slopes of Norway

The Geological Survey of Norway is currently developing a database for unstable rock slopes in Norway. The database is intended to serve three main purposes: (1) to serve as a national archive for potential unstable slopes for use in hazard and risk analysis, aerial planning and mitigation work as well as research; (2) to serve as a robust and easy to use database during field mapping of unstable rock slopes; (3) provide a public available database accessible through an online web map service. The database structure contains several feature classes storing both raw and processed data, including structures, lineaments, displacement measurements, run-out areas and other observations. All feature classes are linked to one main point which holds a general summary for each unstable slope.

Satellite and Ground-Based Interferometric Radar Observations of an Active Rockslide in Northern Norway

Satellite and ground-based interferometric radars have the potential to measure the displacement of active rockslides. Data describing the spatial- and temporal displacement patterns of a rockslide are essential contributions to the total understanding of a rockslide. A better overview of the kinematics will in turn improve the quality of a risk assessment. In this study we have processed TerraSAR-X satellite data, collected since 2009, from both ascending and descending satellite tracks together with ground-based interferometric radar observations of an active rockslide in Northern Norway. Findings show that both the satellite and the ground-based data delimit the active rockslide area and that the displacement rates are highest in the upper part of the rockslide. In the lower parts of the rockslide, the displacement pattern shows a possible compressional toe-zone together with a fast moving lobate shaped landform.

The Role of Inherited Structures in Deep Seated Slope Failures in Kåfjorden, Norway

From studies of orthophotos and through field work, a complex deformation pattern has been recognized in the Lyngen area, Troms, Norway. The area is among the most alpine in Norway and contains a strong clustering of rock slope failures. The rock slope failures are characterized by two different deformation styles, and the difference in style is geographically separated by a fjord and valley lineament. Field studies suggest that two directions of tension oriented almost perpendicular to each other, utilize pre-existing brittle to brittle/ductile fabrics inherited from much older deformation events. The NE-SW direction of tension is parallel to the average displacement vector pointing down-dip along inherited faults. This vector is gravitationally controlled. The NW-SE displacement vector trends strike-parallel along the inherited faults. The presence of the latter appears to be confined geographically.

The Use of Remote Sensing Techniques and Runout Analysis for Hazard Assessment of an Unstable Rock Slope at Storhaugen, Manndalen, Norway

Consequences of catastrophic rock slope failures (i.e. rock avalanches) are usually of large magnitude as they can run across large areas and can trigger secondary processes (e.g. displacement waves, river damming, valley flooding) that can produce large economic and life losses. Early detection of rock slope instabilities and definition of their hazard zones can help society to reduce the impact of these catastrophic failures. This contribution presents the results of the analysis done for an area in the Manndalen Valley, northern Norway. The site has been monitored by remote sensing techniques and the possible runout areas of a catastrophic failure have been defined using numerical modeling for three volume scenarios. Results show that the hazardous area is limited to the eastern valley flank and part of the valley bottom with no secondary processes triggered by the rock avalanche event.