Abstract
Understanding landslide behavior over medium and long timescales is crucial for predicting landslide hazard and constructing accurate landscape evolution models. The behavior of landslides in soil that undergo periodic displacements, termed earthflows or compound soil slides, is especially difficult to forecast at these timescales. This is because velocities can increase by orders of magnitude over annual to decadal timescales, due to processes such as changing recharge conditions, erosion of the landslide toe, and retrogression of the landslide head. In this paper, we provide a detailed analysis of the Schlucher landslide, an unusual earthflow that is perched above the village of Malbun, Liechtenstein. This landslide had been displacing by 10 to 20 cm/year until 2015, when displacements on the order of 2 m/year occurred from 2016 to 2018. These large displacements damaged landslide mitigation measures, caused numerous surface deformation features, and threatened the local population downstream of the earthflow. This landslide has an unusually long monitoring record, with accurate displacement and climatic data available since 1983. We analyze this nearly 40-year monitoring time series to estimate recharge from snowmelt and rainfall, and its correlation with displacement. We also analyze recently collected, high-resolution surface and subsurface data in order to understand landslide response to recharge, landslide kinematics through time, and catastrophic failure potential. We find that interannual displacements can be explained with variations in recharge; however, periodic surges with recurrence times of tens of years must be explained by other mechanisms. In particular, recharge into the landslide during the recent acceleration (2016 to 2018) was not anomalously high. Instead, we argue that loss of internal strength is responsible for this recent acceleration period, and that this mechanism should be considered when forecasting the surge potential for certain earthflows and soil slides.
Highlights
Landslides in soil that undergo periodic, slow to rapid displacements are among the most difficult types of landslides to understand and predict
This paper presents and analyzes the exceptional, long-term monitoring data of the Schlucher landslide, an unusual earthflow located in Liechtenstein
Predicting velocities at the annual and decadal timescales is crucial for understanding landscape evolution and future landslide risk
Summary
Landslides in soil that undergo periodic, slow to rapid displacements are among the most difficult types of landslides to understand and predict. The typical risk posed is to infrastructure, and risk to life is expected to be low, catastrophic failure can occur in some rare cases (Fletcher et al 2002; Aaron et al 2017, 2019) These landslides represent an important sediment source in some landscapes (Keefer and Jonhnson 1983; Fletcher et al 2002; Mackey and Roering 2011). Understanding and predicting the motion of earthflows and compound soil slides require detailed knowledge of landslide response to recharge, as well as landslide kinematics When analyzing these factors, it is important to select a timescale of analysis, due to the fact that time-dependent changes in landslide velocity must be accounted for (Mackey et al 2009; Mackey and Roering 2011; Nereson and Finnegan 2018). We consider the daily to decadal timescales, over which monitoring data is occasionally available (Nereson and Finnegan 2018)
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