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Landslide dams are an important component of slope-fluvial systems, particularly given their potentially disastrous consequences if they breach suddenly. To further research on dam longevity, stability, and failure mechanisms effectively, comprehensive landslide dam dataset are essential. Yet, such datasets from around the world are heterogeneous in their completeness and data-collection approaches, and we still see many geographical “blind spots” where research on landslide dams appears absent, at least within the published literature.As part of a project to collate and compile a global, accessible landslide-dam database, we present some of the challenges involved in its construction. In addition to data heterogeneity and data gaps, biases and parameter definitions will be discussed and highlighted by several landslide-dam case studies from around the world. The aim of the discussion is to acknowledge these data biases, such as geopolitics, funding, accessibility, and triggering-event factors, and offer solutions for the global research community. We will also clearly define terms that have been vague in landslide-dam research so far. For example, dam height, volume, length and width are not used consistently – even what exactly constitutes a landslide dam can sometimes be a defined differently.

As part of a GNS Science (GNS) landslide response to Cyclone Gabrielle (12–16 February 2023), GNS scientists were asked by the National Emergency Management Agency (NEMA), via a request from Gisborne District Council (GDC), for help to investigate the Tokomaru Bay / Mangahauini landslide dam (‘Mangahauini dam’). The Mangahauini dam formed during Cyclone Gabrielle when a landslide blocked the Mangahauini River, approximately 3 km upstream of Tokomaru Bay township. The landslide dam was identified by GDC as being a potential hazard that could pose a risk to life, property and infrastructure downstream if an outburst flood (from a sudden dam breach) were to occur. The hazard that such dams pose can be highly uncertain given the large number of factors that influence their stability and subsequent debris inundation if/when they breach. The landslide response consisted of two site visits, surveying and landslide dam-breach inundation simulations. Prior to an initial aerial reconnaissance survey of the dam on 20 February 2023, the dam had partially breached and a spillway had formed. Nonetheless, following this visit, numerical modelling was undertaken to indicate the extent of dam-breach inundation if the remaining dam material and lake were to fail suddenly. An additional field survey was carried out on 3 March 2023 and included Global Navigation Satellite System (GNSS) and Remotely Piloted Aircraft System (RPAS)-mounted LiDAR (Light Detection and Ranging) surveys of the landslide, landslide dam and lake to estimate their volumes more accurately. Dam-breach models were re-run with the updated volume estimates, and the results were provided to GDC. At the time of surveying (3 March 2023), the Mangahauini River was flowing through the dam along a relatively wide spillway, partly developed along State Highway 35, and there was only a small, impounded lake behind the dam with an estimated volume of ~80,000 m3 . Based on our field surveys and numerical simulations, two potential end-member scenarios regarding the hazard (not the risk) posed by the dam were identified: 1. Lake continues to gradually drain via the spillway through the dam – the current scenario, and thought to be the ‘best case’ scenario, with the following conditions and impacts:The lake continues to drain through the existing channel without sudden and complete failure of the dam and lake; Water gradually erodes and incises the existing dam debris and spillway; Floodwater and debris inundation downstream outside of active river channel less likely to occur. 2. Re-damming of the river due to remobilised landslide debris or wood, perhaps in a future storm – thought to be the ‘worst case’ scenario, with the following conditions and impacts: Up to 320,000 m3 of potentially unstable debris remains on the slope above the Mangahauini River valley, and; If this debris from the slope above the dam or farther upstream were to remobilise and re-dam the river, then the lake could increase in size, which; Could result in potential for larger (rapid) dam failure, which could lead to inundation downstream by dam-breach floodwater and debris; This scenario is highly uncertain, as it depends on the volume of debris remobilised, which affects the volume and geometry of any potential dam and impounded lake, and the (unknown) stability of the dam material.

An extreme winter storm travelled across New Zealand on the 16th to 18th of July 2021, affecting the Marlborough, Tasman, Nelson, West Coast and Wellington regions. Flooding and landslides resulted in evacuation of numerous communities and damage to transport networks and property in these regions. Multiple roads were closed and houses impacted by landslides, particularly in the Buller River Valley and Marlborough. Following the storm, GNS Science and Marlborough District Council staff completed reconnaissance in the area to determine the extent of damage from landslides to infrastructure and communities, including a five-hour helicopter flight and three days of detailed site visits and surveys. The site visits involved collecting UAV (drone) imagery to create 3D photogrammetric models, characterising 11 landslides, and assessing the damage and impact to 18 residential buildings, including the state or condition of damage sustained from landslides. In addition, the safety colour tagging and habitability of buildings were recorded. Analysis of rainfall data indicates that 400���500 mm of rain fell over 54 hours (annual return intervals [ARIs] > 250 years) for most of the Wairau north bank hill country and Marlborough Sounds regions, with localised rainfall intensities exceeding 25 mm/hr in several large areas (ARIs 2���10 years). Antecedent soil moisture conditions were relatively high following frequent rainfall over the previous months. Landslides occurred in all vegetation cover types in areas of high rainfall, including indigenous forest, regenerating indigenous forest and scrub, exotic forestry and pasture. Recently harvested or replanted exotic forest plantations were most susceptible to landsliding, but slopes with exotic forest and pasture, as well as with regenerating indigenous forest and scrub, were also commonly affected. Debris avalanches and debris flows were the most common landslide types and frequently initiated at the contact between bedrock and overlying colluvium. Many of the observed landslides entrained significant large woody debris, which caused substantial damage to buildings. Of the 18 residential buildings surveyed, 10 were deemed uninhabitable. Fortunately, no deaths or injuries were reported, as most of the affected houses were vacant during the event. Data collected will be included in the development of a rainfall-induced landslide prediction tool. In addition, the information presented here will be used in combination with numerical landslide runout model hazard intensity outputs (e.g. debris flow height) to develop landslide vulnerability functions for New Zealand buildings. The information may also be used to better understand landslide risks in the study area and aid planning for and mitigating against natural hazards. (The authors)

Ziel dieser Mountainbike-Fachplanung ist es, den Freistaat zu einem der führenden grenzübergreifenden Mountainbike-Reiseziele in Deutschland zu entwickeln. Dafür beschreibt die Planung konkrete Maßnahmen. Als praxisorientiertes Handbuch soll sie zudem als Orientierung bei der Planung und Entwicklung neuer Mountainbike-Angebote dienen. Die Fachplanung zeigt auf, wie vorhandene Infrastrukturen wie Skiliftanlagen und regionale Sehenswürdigkeiten in die Mountainbike-Projekte eingebunden werden können und dadurch besser ausgelastet werden. Ebenfalls deutlich wird der Wirtschaftsfaktoreffekt für die vorhandenen Gastronomie- und Beherbergungsbetriebe entlang und im Umfeld der Strecken. Natur und Kultur erlebbar zu machen, gleichzeitig aber durch gezielte Besucherlenkung zu schützen und zu erhalten, sind zentrale Ansprüche der Fachplanung. Redaktionsschluss: 31.05.2021

The Flims rockslide/rock avalanche (FRRA) is the largest long runout landslide in Europe. This event provides a unique opportunity to study the pre-failure and failure behavior of a large rock slope, as both the source zone and deposit of this event are accessible. In this study, we perform engineering geological and geomorphic field mapping as well as stability and runout modeling in order to explore the preconditioning and triggering factors that resulted in failure of this event, and to infer the mechanisms that governed its runout. By combining these analyses, we qualitatively comment on the mechanisms that lead to the transition from a rockslide to a long runout, catastrophic rock avalanche. Our engineering geological and geomorphic field mapping has revealed that the FRRA failed along a sliding zone that features numerous, large scale steps. Previous work at the site, as well as new analysis of thin sections, has revealed the presence of marl-like layers within the failed stratigraphic unit. Our stability analysis shows that the presence of low strength layers at the depth of the rupture surface is required for failure to initiate, and that failure could be triggered either by strong seismic shaking, elevated pore-water pressures, or a combination of both. The results of the runout analysis show that this event likely remained coherent for a large portion of its motion, and that liquefaction of alluvial sediments at the toe of the slope may have enhanced the runout distance of this rock avalanche. Combining the mapping, stability and runout modeling has shown that the basal shear strength required for the runout analysis is ∼6°–10° lower than that back-analyzed for the stability of this event. Thus, a mechanism to reduce strength along the rupture surface immediately following the initial instability was required for catastrophic failure of this event. This mechanism is poorly understood at present, but is likely crucial for understanding the transition from an initially stable slope to a catastrophic, long runout rock avalanche., Frontiers in Earth Science, 8, ISSN:2296-6463

Geophysical Research Abstracts, 17, ISSN:1029-7006, ISSN:1607-7962

I apply a forensic, multidisciplinary approach that integrates engineering geology field investigations, engineering geomorphology mapping, long-range terrestrial photogrammetry, and a numerical modelling toolbox to two large rock slope failures to study their causes, initiation, kinematics, and dynamics. I demonstrate the significance of endogenic and exogenic processes, both separately and in concert, in contributing to landscape evolution and conditioning slopes for failure, and use geomorphological and geological observations to validate numerical models. The 1963 Vajont Slide in northeast Italy involved a 270-million-m3 carbonate-dominated mass that slid into the newly created Vajont Reservoir, displacing water that overtopped the Vajont Dam and killed 1910 people. Based on literature, maps and imagery, I propose that the landslide was the last phase of slow, deep-seated slope deformation that began after the valley was deglaciated in the Pleistocene. Field and air photograph observations and stream profiles provide the context of Vajont Slide. The first long-range terrestrial digital photogrammetry models of the landslide aid in characterising the failure scar. Analysis of the failure scar emphasises the complexity of the failure surface due to faults and interference between two tectonic fold generations, influencing failure behaviour. Observations of the pre- and post-failure slope and interpretation of numerical simulations suggest a complex three-dimensional active-passive wedge- sliding mechanism, with two main landslide blocks and five sub-blocks in the west block, separated by secondary shear surfaces. The 1959 Madison Canyon Slide in Montana, USA, was triggered by an M = 7.5 earthquake. A 20-million-m3 rock mass descended from the ridge crest, killing 24 people and blocking Madison River to create Earthquake Lake. Marble at the toe of the slope acted as a buttress for weaker schist and gneiss upslope until the earthquake undermined its integrity and triggered failure. Rock mass characterisation, long-range terrestrial digital photogrammetry, and kinematic analysis indicate that the lateral, rear, and basal release surfaces formed a hexahedral wedge-biplanar failure. Dynamic numerical modelling suggests topographic and damage amplification due to ridge geometry and pre-existing tension cracks. Analysis of the case studies highlights the complexity of large, catastrophic rock slope failures, their causes, and their evolution from incipient failure to disaster.

Over the last decades, a movement has begun to reclassify deposits previously misidentified as having origins other than landsliding. The reverse problem of incorrectly assigning deposits a mass movement origin, however, has been addressed less in the landslide community. The Cima Salti Landslide in the Lake Garda region of Northern Italy is a cautionary tale of assuming source areas and volumes. It was traditionally thought to have dammed Tenno Lake in the Middle Ages, and to have a volume of 20–30 Mm3. We show through geological field data and simple runout simulations with the codes DAN3D and SHALTOP (which produced comparable results) that the volume of the landslide was likely significantly overestimated in the past, and that it most likely did not dam Tenno Lake, as has been assumed. We propose that a smaller volume landslide (2–5 Mm3) was deposited on stagnant ice melting in situ in the Lateglacial period, a relatively minor event in the complex history of the Magnone valley. This interpretation emphasizes the importance of careful field investigations and assumption validation, at Cima Salti and in a broader context. It also shows the unique capacity of landslide simulation to guide field observation and discriminate mass emplacement processes.

UAVs, equipped with optical cameras and GPS, are used to obtain high quality aerial photographs. The photos are processed with photogrammetric techniques. Therefore, e"cient flight planning is required. Horizontal flight paths for photogrammetry are optimized by open source programs like the Mission Planner from Ardupilot. When the topography is mountainous or steep, the current flight planning is not ideal. For that reason, a program is written to optimize the flight planning for complex topography. The idea is that the way points lay smoothed and parallel to the landscape surface. Calculated flight plans are tested successful in Attinghausen, Canton of Schwyz and Grimsel, Canton of Berne. Calculated way points and GPS data were compared after the flight to obtain the nearest distance to the ground. The resulting aerial photographs are used to produce a three-dimensional photogrammetric model, an orthophoto and a DEM per flight. Agisoft Photoscan was mainly used for this. The new DEM from Agisoft is compared with the swissALTI3D (older DEM) from swisstopo. Such comparisons are usually applied to detect mass changes. Adam Tech 3DM Analyst is also used to create photogrammetric data of one flight. Orthophotos and DEM of both softwares show good quality with resolutions till 5 mm per pixel.