Establishing regimes of landslide activity - Analysis of landslide triggers over the previous seven decades (Western Carpathians, Poland)

Long-term analyses of landslide patterns and triggering factors, covering several decades of continuous data, including periods of both acceleration and stability, are a key to understanding landslide activity, background, and variability. In this study, we analyse the long-term relationships between landslide activity and the triggering factors, precipitation, and low-magnitude earthquakes for three landslides in the Western Carpathians, Poland. Based on dendrochronological reconstruction covering 68 years (1951-2018), including tree-ring eccentricity and compression wood dating for 107 Norway spruce trees, we determined that there are significant differences in the activity and triggers of the studied slopes. We were able to explain the origin of the differences through the individual features of landslide topography and structure, such as the depth of the shear zones, disintegration of landslide blocks resulting in a plastic, flow-like movement of the material, and location of the landslide blocks in relation to high groundwater levels in the valley floors. Finally, we determined the optimal sequences of triggers leading to heavy landsliding for each slope, therefore establishing the regimes of their activity. We argue that the long-term regularities in landslide response to triggers can be generalised into regimes, as is commonly done with river discharge, groundwater levels, and their hydro-meteorological background. We propose establishing regimes of landslide activity that are based on decades of observations and reconstructions. Our study demonstrates that such a long-term approach can be an efficient tool for describing and explaining the variability of landslide activity and hazards over space and time.

Automated summary

This study analyzed the long-term relationships between landslide activity and triggering factors in the Western Carpathians, Poland over a period of 68 years. Significant differences in activity and triggers were identified, with explanations provided through individual features of landslide topography and structure. Optimal sequences of triggers leading to heavy landsliding for each slope were determined, establishing regimes of activity. The study demonstrates the efficiency of a long-term approach in describing and explaining landslide activity and hazards over space and time.