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Latest advances in topographic data acquisition techniques have greatly enhanced the possibility to analyse landscapes in order to understand the processes that shaped them. High-resolution Digital Elevation Models (DEMs), such as LiDAR-derived ones, provide detailed topographic information. In particular, if multi-temporal DEMs are available, it is possible to carry out a detailed geomorphic change detection analysis. This analysis may provide information about the dynamics of large landslides and may thus, be useful for landslide risk assessments. However, LiDAR-derived DEMs are mostly available only as post-event surveys. The technique is relatively recent, and local or national authorities only started widespread surveys in the last decade. Therefore, it is of a certain interest to analyse the effectiveness of DEMs derived from technical cartography to produce reliable volumetric estimates related to large landslides. This study evaluates the use of a multi-source DEM of Difference (DoD) analysis for the investigation of a large landslide –Le Laste–, which occurred on November 12, 2014 on Mount Antelao (eastern Italian Alps). The landslide initiated as a 365,000 m3 rockslide close to the summit of the mountain and transformed into a debris avalanche during its runout. The comparison of pre- and post-event DEMs allowed for the identification and quantification of erosion and deposition areas, and for the estimation of landslide volume. A sound back-analysis of the landslide with the 3D numerical model DAN3D was based on this comparison and on seismic records of the event. These seismic records proved to be remarkably useful, as they allowed for the calibration of the simulated landslide velocity. This ensured the reliability of the model notwithstanding the topographic datasets, intrinsic uncertainties. We found that using a pre-event DEM derived from technical cartography tends to slightly overestimate the volume with respect to the use of the more accurate LiDAR-derived DEM. In recent years, the landslide risk around Mt. Antelao has been increasing alongside the ever-growing population and human activities in the area. Sediment accumulations produced by the Le Laste landslide significantly amplified the debris flow hazard by providing new sediment sources. Therefore, it is crucial to delineate the distribution of this material to enable an adequate debris flow hazard assessment. The material properties derived from the back-analysis of the Le Laste landslide can be used to simulate the runout of possible future events, and to generate reliable hazard zone maps, which are necessary for effective risk mitigation.

<p class="ThesisTitle2NoList"><span lang="EN-GB">Submarine landslides are common on all sediment bearing submarine slopes worldwide. They have the potential to damage expensive subsea infrastructure such as pipelines or telecommunication cables, and generate hazardous tsunamis.</span> <span lang="EN-GB">Numerous studies have shown that weak layers embedded within the slope stratigraphy play a crucial role in controlling the formation of submarine landslides; however, very little is known about their internal structure and composition. Although weak layers seem to be an essential pre-conditioning factor for slope failure, many questions remain unanswered, such as where with respect to weak layers do failure planes form: within the weak layer, above or below it? Previous studies usually relied on sedimentological and geotechnical sediment core and in-situ analyses to investigate weak layers. These analyses, however, do not provide insights into the internal structure of the sediments on a micro-scale level and hence, lack information needed to qualitatively and quantitatively investigate weak layers. </span></p> <p class="ThesisTitle2NoList"><span lang="EN-GB">Here, we present a new approach towards weak layer investigation that is based on high-resolution micro-Computed Tomography (µCT) imaging. µCT is used to visualise, and qualitatively and quantitatively investigate selected sediment samples taken from within weak layers and the background sediment of submarine landslides. Our results show clear compositional and structural differences between individual sub-units of the investigated weak layers, as well as the background sediment. These differences can be attributed partly to different sediment types, i.e. coarse- versus fine-grained sediments, but also reveal a dependency on the sedimentation regime. We find that pore space distribution is highly spatially variable and works on a sub-millimetre scale. Such high variability may be masked by standard bulk porosity measurements, which require larger (several centimetre) sediment samples and only provide information averaged over the entire sample. The identification of small-scale changes, however, appears to be crucial for the formation of weak layers. Our results therefore demonstrate the huge potential of µCT to investigate the internal structure of weak layers, obtaining information that is not resolved and lost in other analytical methods.</span></p>

We have successfully constructed and tested a new, portable, Hybrid Lister‐Outrigger (HyLO) probe designed to measure geothermal gradients in submarine environments. The lightweight, low‐cost probe is 1–3 m long and contains 4–12 semiconductor temperature sensors that have a temperature resolution of 0.002°C, a sample rate of <2 s, and a maximum working depth of ~2,100 m below sea level (mbsl). Probe endurance is continuous via ship power to water depths of ~700 mbsl or up to ~1 week on batteries in depths >500 mbsl. Data are saved on solid‐state disks, transferred directly to the ship during deployment via a data cable, or transmitted via Bluetooth when the probe is at the sea surface. The probe contains an accelerometer to measure tilt, internal pressure, temperature, and humidity gauges. Key advantages of this probe include (1) near‐real‐time temperature measurements and data transfer; (2) a low‐cost, transportable, and lightweight design; (3) easy and rapid two‐point attachment to a gravity corer, (4) short (3–5 min) thermal response times; (5) high temporal/spatial resolution; and (6) longer deployment endurance compared to traditional methods. We successfully tested the probe both in lakes and during sea trials in May 2019 offshore Montserrat during the R/V Meteor Cruise 154/2. Probe‐measured thermal gradients were consistent with seafloor ocean‐drilling temperature measurements. Ongoing probe improvements include the addition of real‐time bottom‐camera feeds and long‐term (6–12 months) deployment for monitoring.