Reginald L. Hermanns

Tephrochronologic Constraints on Temporal Distribution of Large Landslides in Northwest Argentina

Two morphologic settings in the northwestern Argentine prone to giant mountain‐front collapse—deeply incised narrow valleys and steep range fronts bordering broad piedmonts—were analyzed through detailed investigations of fossil landslides and related fluvio‐lacustrine sediments. Nine different rhyodactic tephra layers were defined by geochemical fingerprinting of glass, morphology of pumice, stratigraphic relationships, and mineralogy. The age of three tephra could be determined either directly by 40Ar/39Ar dating or relatively by 14C dating of associated sediments: Paranilla Ash ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Hazard and Risk Classification for Large Unstable Rock Slopes in Norway

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Approach for Systematic Rockslide Mapping of Unstable Rock Slopes in Norway

\end{document} ka), Quebrada del Tonco Ash (∼30 ka), and Alemanía Ash (∼3.7 ka). These units permit correlation of several spatially separate landslide deposits. Landslide deposits in narrow valleys were generated in the late Pleistocene between 40 and 25 ka and in the Holocene since ca. 5 ka and correspond to periods characterized by increased humidity in subtropical South America. In contrast, the age of large landslides in piedmont regions is significantly greater but more difficult to define by tephrochronology. However, selected deposits from this second environment have cosmogenic nuclide exposure ages of 140–400 ka. Because of the large distance of the collapsed mountain fronts from eroding streams and because of important Quaternary displacement along the mountain‐bounding faults, we suggest that strong, low‐frequency seismic activity is the most likely trigger mechanism for most of the landslides in this environment.

Database of Unstable Rock Slopes of 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 Assessment of Unstable and Potential Unstable Rock Slopes in Storfjord (Western 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.

Catalogue of Historical Displacement Waves and Landslide-Triggered Tsunamis in Norway

Displacement waves generated by subaerial landslides can have devastating effects and extend impacts of a landslide tens of kilometres or more. Most research has involved characterization of individual events and, in some cases, comparison of a few events. We have begun to broaden understanding of the phenomenon by compiling a preliminary global catalogue of landslide-generated displacement waves that provides insights into their geographic distribution, size, frequency, and range of mechanisms and impacts. The catalogue is based on a review of published case studies, tsunami catalogues, and the Norwegian national landslide database. It contains 254 events from the fourteenth century AD to 2012. Greater event density in regions with longer written histories, in areas with more settlement, and in the more recent part of the record suggests spatial and temporal biases in documentation and recording. Despite these biases, the spatial pattern of events suggests settings—likely determined by geologic, physiographic and tectonic controls—with elevated hazards that can help focus hazard investigation and mitigation. The diversity of events helps identify differences in displacement wave processes and their resulting impacts, such as wave run-up and travel distance.

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

Systematic mapping of unstable rock slopes has been carried out in Norway since 2005. More than 300 unstable or potential unstable rock slopes have been detected and characterized so far. This utilises a standardized hazard and risk classification system that was established in 2012. The determination of the hazard and risk level follows a new standard approach for the systematic mapping of the analyzed sites that is iterative, starting with simple assessments. However the higher the hazard/risk level of a site is, the larger the amount of geological information collected, and the more detailed the run-out models and consequence analyses that will be carried out. This approach allows mapping resources to be focused on sites with higher risk level, delivering products with different levels of detail. Rock slope failures that would not result in any loss of life, as there is no life line or building in the run-out area, are mapped without a probability assessment. These analyses thus have no scale for the hazard class. Rock slope failures that can result in loss of life are analyzed using qualitative hazard analyses, thus the mapping products are hazard maps with qualitative probability classes. The work on this mapping approach is still ongoing; methods for assessment of the occurrence and consequences of secondary processes (e.g., triggering of displacement waves in water bodies, river damming and outburst floods) need still to be defined. An iterative approach will also be developed to analyze those processes.

Rockslide Dams in Møre og Romsdal County, 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.