Landslide and ravine distributions related to ground conditions in elevated marine deposit in Mid-Norway

The Trondheim and Gauldal areas in Mid-Norway are characterized by thick marine deposits from the ice age and deglaciation period. The following glacio-isostatic rebound has led to river incisions in the valleys and extensive landsliding and ravine erosion. This study is based on data from an upgraded Quaternary geological map of this region for the areas below the highest sea level after the last ice age, with a focus on landslide scars and ravines. The study has a multidisciplinary approach, which is important in order to get a good regional geological understanding of the ground conditions and the landscape development. This means that geological, geomorphological, geotechnical, geophysical and hydrogeological data are used. The study area is divided into six parts, based on natural topographical divisions and the distribution of landslide scars and ravines. Factors influencing the development of sensitive clay and the triggering of landslides are described for each area; these include sediment distribution, thicknesses and stratigraphy, bedrock topography, the degree of leaching of clay, groundwater conditions, the number, size and shape of landslides, and the distribution of rivers, streams and ravines. The study shows that the size, behaviour and erosional potential of the main river or stream influence the landscape development to a high degree. The erosional basis, stratigraphy and presence of bedrock are essential for leaching and the development of quick clay.