Landslides are one of the most significant natural hazards worldwide. They can have far-reaching negative impacts on societies in different socio-economic sectors as well as on the landscape. Among the different types and processes that can also affect infrastructure and land use planning, slow-moving landslides are often underestimated. Therefore, studying areas affected by slow movements provide an opportunity to better understand the spatial and temporal patterns of these processes, their forcings, mechanisms, and potential risks. This study aims to investigate the importance of historical data for improving landslide hazard assessment in Lower Austria (Austria), which is particularly prone to landslides. This paper focuses on how historical information formed the basis for the establishment of three long-term landslide monitoring observatories in this region. The analysis conducted highlights the importance of using historical data to better assess the frequency and magnitude relationships and phases of landslide activity. In particular, they can extend the temporal window and provide relevant information on past events and accelerations to improve knowledge of landslide dynamics and the resulting socio-economic impacts. In order to better assess the landslide hazard associated, it is necessary to integrate historical data and monitoring datasets obtained by surface and subsurface methods. Both components allow for the characterization of the spatio-temporal evolution of slow movements and the analysis of the hazard over time. Based on a variety of historical sources, it was possible to install the instruments constituting the long-term landslide monitoring observatories in a meaningful manner. The results demonstrate the influential role of human impact on the stability conditions, which may also contribute to landslide occurrence. In this regard, the attempt to combine historical data and long-term, continuous monitoring systems in the presented landslide observatories can improve landslide risk reduction measures in the region. The integration of different techniques and tools, along with ongoing research and collaboration with local authorities, will further improve our understanding of these slow-moving processes and the development of effective management strategies.

Soil moisture plays a crucial role in landslide research as it directly influences slope stability and the occurrence of landslides. The amount of water present in the soil significantly impacts its strength and cohesion. Excessive soil moisture, especially during periods of heavy rainfall, can reduce the frictional resistance within the soil, leading to a decrease in shear strength and an increased likelihood of landslides. The province of Lower Austria is situated in a region highly prone to landslides due to its specific geological characteristics. The prevailing geological formations consist mainly of the Flysch and the Klippen Zone, characterized by mechanically weak units comprising intercalated limestones and deeply weathered materials. These geological conditions, coupled with hydrological factors, changes in land use, and various anthropogenic influences, collectively contribute to the inherent instability of the region.Monitoring and understanding soil moisture levels provide valuable insights into the predisposing and triggering factors, potentially enhancing the prediction and mitigation of these hazardous events. Advancements in technologies like Cosmic Rays Neutron Sensing (CRNS) enables to obtain spatially averaged soil moisture measurements, offering a more comprehensive understanding of moisture distribution across different scales. The defining characteristic of (CRNS) technology lies in its ability to directly measure water content, naturally averaged within a volume known as the footprint. This volume encompasses a horizontal extension with a radius spanning up to hundreds of meters and penetrates the soil to depths of tens of centimeters. This is widely acknowledged as the primary advantage of the CRNS probe compared to point-scale measurements, as it yields a valuable representative value for water availability in the designated area. In this study, we apply CRNS at a slow-moving landslide in Lower Austria and explore its potential.

Landslides are one of the most important and frequent geological hazards worldwide. Among the many different types and processes, slow and very slow mass movements are often underestimated, even if they can impact local infrastructures and permanently affect agricultural practices and land use planning. Slow-moving landslides are common in clay-rich layers and areas that are typically characterized by mechanically weak materials. In the field of slow-moving landslide monitoring, understanding the factors driving the slope instability is the key to assessing the landslide hazard and to supporting local authorities in hazard management.In this study, the first results of an ongoing monitoring setup for a complex, slow-moving earth-slide system in Lower Austria are presented. The Brandstatt landslide is located in a complex geological transition zone between the Flysch and Klippen zones, which is known to be prone to shallow and deep landslides because its susceptibility to sliding processes has been investigated in recent years. Considering the predisposing conditions (geological and climatic settings), the unstable slope can be considered as a representative site of complex landslide processes in this region.Landslide movements monitoring includes a combination of surface and subsurface methods to investigate the spatio-temporal evolution of factors that prepare, trigger, and control landslide dynamics. Geological characterization of the subsurface was obtained through a dynamic penetration test (DPH) campaign and percussion drilling. In addition, the subsurface displacements and potential shear planes were evaluated using repeated inclinometric measurements. A meteorological station is also installed on-site, as well as piezometers and time-domain reflectometry (TDR) sensors in selected locations on the slope. These instruments provide high temporal resolution data, which are automatically transmitted to a server for the real-time monitoring of hydrometeorological conditions. However, the monitoring strategy to detect surficial changes is currently limited to the application of Terrestrial Laser Scanning (TLS) because an Unmanned Aerial Vehicle (UAV)-based Structure from Motion (SfM) is not possible for vegetation cover issues.The current results suggest the following: i) the connection between soil properties, soil moisture, and changes in groundwater level in the evolution of the slope instability, ii) potential shear surfaces within the shallow layers of the unstable slope, and iii) the importance of combining hydrological and geotechnical monitoring to set up an integrated network for landslide interpretation. Accordingly, obtaining information from a multi-parameter monitoring system is fundamental to identifying the relationship between the triggering and kinematic mechanisms of a complex, slow-moving landslide. However, the nonlinear behavior of slow movements restricts the temporal capability to properly understand the processes of complex mass movements. Consequently, landslide dynamics need to be further understood to establish a long-term monitoring system.