Historical Landslide Events Research Articles

Spatial and temporal variations of Norwegian geohazards in a changing climate, the GeoExtreme Project

Abstract. Various types of slope processes, mainly landslides and avalanches (snow, rock, clay and debris) pose together with floods the main geohazards in Norway. Landslides and avalanches have caused more than 2000 casualties and considerable damage to infrastructure over the last 150 years. The interdisciplinary research project "GeoExtreme" focuses on investigating the coupling between meteorological factors and landslides and avalanches, extrapolating this into the near future with a changing climate and estimating the socioeconomic implications. The main objective of the project is to predict future geohazard changes in a changing climate. A database consisting of more than 20 000 recorded historical events have been coupled with a meteorological database to assess the predictability of landslides and avalanches caused by meteorological conditions. Present day climate and near future climate scenarios are modelled with a global climate model on a stretched grid, focusing on extreme weather events in Norway. The effects of climate change on landslides and avalanche activity are studied in four selected areas covering the most important climatic regions in Norway. The statistical analysis of historical landslide and avalanche events versus weather observations shows strong regional differences in the country. Avalanches show the best correlation with weather events while landslides and rockfalls are less correlated. The new climate modelling approach applying spectral nudging to achieve a regional downscaling for Norway proves to reproduce extreme events of precipitation much better than conventional modelling approaches. Detailed studies of slope stabilities in one of the selected study area show a high sensitivity of slope stability in a changed precipitation regime. The value of elements at risk was estimated in one study area using a GIS based approach that includes an estimation of the values within given present state hazard zones. The ongoing project will apply the future climate scenarios to predict the changes in geohazard levels, as well as an evaluation of the resulting socioeconomic effects on the Norwegian society in the coming 50 years.

Evaluation of seismic effects on the landslide deposits of Monte Salta (Eastern Italian Alps) using distinct element method

Abstract. The aim of the paper is to present the modelling of the ground effects of seismic waves on a large debris deposit lying on a steep mountain slope, with particular attention paid to the potential triggering of slope movements. The study site is a mass of 2.5 million m3 rock fall deposit, named "Monte Salta Landslide", located on the northern slope of the Vajont valley, at the border between Veneto and Friuli Venezia Giulia regions in north-eastern Italy. Several historical landslide events were reported in the area in the past, first one dating back to the 17th century. The landslide deposit completely mantles the slope with a thick cover of rock blocks. The Mt. Salta landslide is conditioned by the presence of Mt. Borgà regional thrust, which uplifts Jurassic limestone on the top of Cretaceous rock units. Above the thrust zone, folded and highly fractured rock mass dips steeply towards the slope free face, producing highly unstable setting. The study area has been classified as high seismic hazard and different vulnerable elements can be affected by the remobilisation of debris, among which a village, a national road and a big quarry that was opened, with the intent to exploit the part of the landslide deposit for construction purposes. In this study, numerical analysis was performed, to simulate the slope behaviour using distinct element method and applying UDEC code. The 2-D models were built on three cross-sections and elasto-plastic behaviour was assumed, both for rock matrix and discontinuities. The earthquake effect was modelled in pseudo-dynamic way, i.e. by magnifying the acceleration and applying also its horizontal component. The expected seismic acceleration in the study area was calculated on the basis of previous studies as equal to 0.28 g. The results proved that the increase of the vertical component alone has a small influence on the deformational behaviour of the system. Hence, the acceleration vector was deviated at 5° and then at 10° from the vertical. A small increment of the displacement was observed in the first case, whereas very large movements occurred in the second. Therefore, it can be concluded that, besides the magnitude of the earthquake, even small seismic waves in horizontal direction could trigger significant movements and therefore hazardous conditions. The modelled scenario should be helpful for planning of the functional countermeasure works and civil defence evacuation plan.

Historical landslides in Nicaragua—collection and analysis of data

The results of the first investigation on historical landslides that occurred in Nicaragua before 1990 are presented. The paper shows how the analysis of historical documents can provide important information about the type and the temporal and spatial distribution of landslide events, especially for countries where landslide investigation is a young discipline. The methodology included research of historical sources at national institutions, public libraries, international journals, the Internet, and the collection of original texts from newspapers and their transcription in analog format. Analysis and interpretation of the data was performed, followed up by the digitalization of landslide spatial locations using the software ArcGIS and the integration of the landslide attributes in a structured query language (SQL) server database. Finally, the analysis of the stored data was done using SQL interactive queries. The type and quality of the historical sources available are described. Limitations and problems, common in the preparation of any historical catalogue, and possible sources of error derived from the collection, interpretation, and storage of the data are discussed as well. One hundred thirty-five historical landslides were identified. The study shows that these events occurred mostly in combination with other natural phenomena. The collected data were used to construct a geo-referenced inventory of historical landslide events, including information about damage and human losses caused by them. The inventory provides the basis for a more comprehensive landslide hazard assessment in Nicaragua.