Downhill Progressive Landslides in Long Natural Slopes : Triggering Agents and Landslide Phases modeled with a Finite Difference Method

A large landslide in Tuve (Gothenburg, Sweden 1977) initiated the development of a model for slope stability analysis taking the deformation-softening of soft sensitive clays into consideration. The model studies triggering agents and five phases in progressive slope failure are identified: (1) in-situ, (2) disturbance, (3) unstable ‘dynamic’, (4) transitory (or permanent) equilibrium, and (5) ‘global’ failure. The clay resistance in these phases may differ widely; mostly due to different rates of loading. Two time dependent failure criteria are defined: (i) the triggering load condition in the disturbance Phase (2), and (ii) the transitory equilibrium in Phase (4), indicating whether minor downhill displacements or a veritable landslide catastrophe will occur. The analysis explains why downhill landslides tend to spread over vast areas of almost horizontal ground further down-slope. The model has been applied to landslides in Scandinavia and Canada. Three case studies are briefly discussed. The model is a finite difference approach, where local downhill deformations caused by normal forces is maintained compatible with deviatory shear deformations above the potential (or the established) failure surface. Software and an easy-to-use spreadsheet are introduced as well as recent developments. See also Video Abstract.Validerad; 2016; Nivå 2; 2016-11-02 (andbra)</p

Documenting scarce and fragmented residues on stone tools: an experimental approach using optical microscopy and SEM-EDS

Residue analyses are widely applied to studies of stone tool function and can be a powerful method for determining the past tool use(s), especially when combined with other functional investigations such as usewear and technological analysis. Experimental work has shown that optical microscopes and the scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS) are reliable instruments for identifying intact tool residues. However, little experimental work has aimed to document residues that show various stages of degradation or when abundance is low. We combined traditional optical microscopy and the SEM-EDS to identify the advantages and challenges of each technique when looking at progressively smaller and more fragmented residues following more aggressive stages of cleaning, burial and soaking in a weak acid/base solution. We found that large quantities of intact residues on unwashed stone tools show distinctive morphological features under optical microscopes and the SEM-EDS can be used to document residues under extremely high magnifications and to determine their elemental compositions. After the various stages of washing, we found that residues became highly fragmented and were restricted to common stone features like the micro-cracks/scars along the working edge. These residues were often difficult to characterise using optical microscopes but the SEM-EDS proved highly useful. The weak acid/base solutions caused some residues to become physically altered or modified their elemental composition. Buried tools reduced the abundance of use-residues and introduced additional non-use-related contaminant particles that affected EDS measurements and lead to less reliable residue interpretations