The Hidden Hazard Of Melting Ground Ice In Northern Iceland

This thesis explores the morphology, dynamics and causes of landslides and debris flows in mountainous regions of northern Iceland. The primary objectives are to define the initiation and evolution of Icelandic landslides and debris flows, and to understand the link between ground-ice thaw and rapid mass movements. Slopes are predicted to react more intensely to global warming, so improving our knowledge of rapid mass movements in cold environments, which are even more sensitive to climate change, is crucial, as they could pose at risk local population in Iceland and other mountainous periglacial areas. I first perform a detailed study of debris flows in north-western Iceland, distinguishing through quantitative geomorphological methods the different mechanisms of debris-flow initiation and the associated geomorphic features. The approach of this study is easily applicable to similar settings, and its results could help in anticipating new potentially destructive events. Secondly, I describe and quantify the morphometric characteristics of two landslides in northern Iceland, whose source materials comprised ground ice-cemented deposits. This study reveals different dynamic landslide processes and the crucial role of thawing ground ice in landslide emplacement. I then analyse meteorological and seismic data near these two landslides. I define and distinguish precipitation, seismic activity and permafrost degradation as the preparatory and triggering factors for the failures. Finally, through a geomorphic approach I analyse molards, conical mounds of debris that I found in both landslides deposits. I show conclusive evidence that molards form from thawing of blocks of ice-rich sediments that degrade into cones of debris. I demonstrate that molards are the ‘fingerprint” of permafrost degradation, and their different morphology and distribution can reveal different types of landslide processes in periglacial terrains. This thesis widens our knowledge of the conditions and processes controlling rapid mass movements in cold environments, which is crucial in the perspective of hazard assessment, and opens up new avenues for the study of potentially hazardous geomorphic responses of cold landscapes to changing climate conditions

Cost‐effectiveness analysis of revisional Roux‐en‐Y gastric bypass: laparoscopic vs. robot assisted

There is controversy over the possible advantages of the robotic technology in revisional bariatric surgery. The aim of this study is to report the experience of a high-volume bariatric center on revisional Roux-en-Y gastric bypass with robot-assisted (R-rRYGB) and laparoscopic (L-rRYGB) approaches, with regards to operative outcomes and costs. Patients who underwent R-rRYGB and L-rRYGB between 2008 and 2021 were included. Patients’ baseline characteristics and perioperative data were recorded. The primary endpoint was the overall postoperative morbidity. A full economic evaluation was performed. One-way and two-way sensitivity analyses were performed on laparoscopic anastomotic leak and reoperation rates. A total of 194 patients were included: 44 (22.7%) L-rRYGB and 150 (77.3%) R-rRYGB. The robotic approach was associated with lower overall complication rate (10% vs. 22.7%, p = 0.038), longer operative time, and a reduced length of stay compared to L-rRYGB. R-rRYGB was more expensive than L-rRYGB (mean difference 2401.1€, p < 0.001). The incremental cost-effective ratio (ICER) was 18,906.3€/complication and the incremental cost-utility ratio was 48,022.0€/QALY (quality-adjusted life years), that is below the willingness-to-pay threshold. Decision tree analysis showed that L-rRYGB was the most cost-effective strategy in the base-case scenario; a probability of leak ≥ 13%, or a probability of reoperation ≥ 14% following L-rRYGB, or a 12.7% reduction in robotic costs would be required for R-rRYGB to become the most cost-effective strategy. R-rRYGB was associated with higher costs than L-rRYGB in our base-case scenario. However, it is an acceptable alternative from a cost-effectiveness perspective

Cost-effectiveness analysis of revisional Roux-en-Y gastric bypass: laparoscopic vs. robot assisted

There is controversy over the possible advantages of the robotic technology in revisional bariatric surgery. The aim of this study is to report the experience of a high-volume bariatric center on revisional Roux-en-Y gastric bypass with robot-assisted (R-rRYGB) and laparoscopic (L-rRYGB) approaches, with regards to operative outcomes and costs. Patients who underwent R-rRYGB and L-rRYGB between 2008 and 2021 were included. Patients’ baseline characteristics and perioperative data were recorded. The primary endpoint was the overall postoperative morbidity. A full economic evaluation was performed. One-way and two-way sensitivity analyses were performed on laparoscopic anastomotic leak and reoperation rates. A total of 194 patients were included: 44 (22.7%) L-rRYGB and 150 (77.3%) R-rRYGB. The robotic approach was associated with lower overall complication rate (10% vs. 22.7%, p = 0.038), longer operative time, and a reduced length of stay compared to L-rRYGB. R-rRYGB was more expensive than L-rRYGB (mean difference 2401.1€, p < 0.001). The incremental cost-effective ratio (ICER) was 18,906.3€/complication and the incremental cost-utility ratio was 48,022.0€/QALY (quality-adjusted life years), that is below the willingness-to-pay threshold. Decision tree analysis showed that L-rRYGB was the most cost-effective strategy in the base-case scenario; a probability of leak ≥ 13%, or a probability of reoperation ≥ 14% following L-rRYGB, or a 12.7% reduction in robotic costs would be required for R-rRYGB to become the most cost-effective strategy. R-rRYGB was associated with higher costs than L-rRYGB in our base-case scenario. However, it is an acceptable alternative from a cost-effectiveness perspective

Modification of Caloris ejecta blocks by long-lived mass-wasting: A volatile-driven process?

The Caloris basin is the largest well-preserved impact basin on Mercury. As such, Caloris ejecta afford us an opportunity to study material from Mercury’s deep interior with remote sensing. We have made observations of the geomorphology, colour, distribution, and flank slopes of the circum-Caloris knobs. Our observations suggest that these circum-Caloris knobs are modified ejecta blocks from the Caloris impact. High-resolution MESSENGER images show that knobs are conical and relatively uncratered compared with the surrounding plains, which implies the knobs have undergone resurfacing. We have observed material that has sloughed off knobs superposing impact craters that demonstrably postdate the Caloris impact, which requires some knob modification to have been more recent. We have observed hollows, depressions in Mercury’s surface generally believed to have been caused by volatile-loss, on and closely associated with several knobs, which indicates that many knobs contain volatile material and that knob modification could extend into Mercury’s recent past. Our measurements show that knob flanks typically have slopes of ∼21°, which is steep for a mound of unconsolidated material that was originally emplaced ∼3.8 Ga. The conical shape of knobs, their steep slopes, the dearth of superposed craters on knobs, and knob superposition relationships with other landforms suggest that Caloris ejecta blocks of arbitrary original shape were modified into their present shapes by long-lived mass-wasting. Mass-wasting must have dominated over impact gardening, which would have produced domal morphologies only. We suggest that mass-wasting was probably driven by volatile-loss, in a manner analogous to terrestrial landforms called ‘molards’. If the circum-Caloris knobs are analogous to molards, then they represent a landform and a process hitherto undocumented on Mercury, with implications for the volatile content of the planet’s interior. These knobs therefore are prime targets for BepiColombo, which could search for fresh failures and volatile exposures in the knobs

Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

Debris flows are fast‐moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris‐flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris‐flow release styles by integrating high‐resolution multi‐temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris‐flow triggering processes were previously hypothesized for this site: (i) slope failure, characterised by landslides evolving into debris flows, and (ii) the fire‐hose effect, in which debris accumulated in pre‐existing, steep‐sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris‐flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire‐hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source‐area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire‐hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris‐flow initiation in absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows

Molards as an indicator of permafrost degradation and landslide processes

Molards have been defined in the past as conical mounds of debris that can form part of a landslide's deposits. We present the first conclusive evidence that molards in permafrost terrains are cones of loose debris that result from thawing of frozen blocks of ice-rich sediments mobilised by a landslide, and hence propose a rigorous definition of this landform in permafrost environments. We show that molards can be used as an indicator of permafrost degradation, and that their morphometry and spatial distribution give valuable insights into landslide dynamics in permafrost environments. We demonstrate that molards are readily recognisable not only in the field, but also in remote sensing data; surveys of historic aerial imagery allow the recognition of relict molards, which can be used as an indicator of current and past permafrost conditions. The triggering of landslides as a result of permafrost degradation will arguably occur more often as global atmospheric temperatures increase, so molards should be added to our armoury for tracking climate change, as well as helping us to understand landslide-related hazards. Finally, we have also identified candidate molards on Mars, so molards can inform about landscape evolution on Earth and other planetary bodies

Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

Debris flows are fast-moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris-flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris-flow release styles by integrating high-resolution multi temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris-flow triggering processes were previously hypothesized for this site: (i) slope failure, characterised by landslides evolving into debris flows, and (ii) the fire-hose effect, in which debris accumulated in pre-existing, steep-sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris-flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire-hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source-area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire-hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris-flow initiation in absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows

Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

Publisher's version (útgefin grein)Debris flows are fast-moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris-flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris-flow release styles by integrating high-resolution multi-temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris-flow triggering processes were previously hypothesised for this site: (i) slope failure, characterised by landslides evolving into debris flows; and (ii) the fire-hose effect, in which debris accumulated in pre-existing, steep-sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris-flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire-hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source-area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire-hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris-flow initiation in the absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows.This work would not have been possible without a postgraduate studentship grant (NE/L002493/1) from the CENTA Doctoral Training Partnership funded by the UK Natural Environment Research Council (NERC) and the British Geological Survey University Funding Initiative Studentship (GA/14S/024, Ref: 284). We thank the NERC Airborne Research Facility Data Analysis Node for obtaining the aerial photography and LiDAR data, for the airborne survey project NERC ARSF 07217a in 2007 and for the airborne survey project NERC ARSF IG13‐11 in 2013. We thank the NERC Geophysical Equipment Facility for technical support and for the loan number 1001. We would like to show our gratitude to Jón Kristinn Helgason (Icelandic Meteorological Office), who provided expertise that greatly improved the manuscript. We acknowledge constructive comments and suggestions from two anonymous reviewers. C. Jordan publishes with permission from the Executive Director of the British Geological Survey.Peer Reviewe

The impact of ground-ice thaw on landslide geomorphology and dynamics: two case studies in northern Iceland

As consequence of ongoing climate change, permafrost degradation is thought to be increasingly affecting slope stability in periglacial environments. This is of growing concern in Iceland, where in the last decade, permafrost degradation has been identified among the triggering factors of landslides. The role of ground ice in conditioning the morphology and dynamics of landslides involving loose deposits is poorly understood. We show the geomorphological impact of the Móafellshyrna and Árnesfjall landslides that recently occurred in ice-cemented talus deposits in northern Iceland. Using field and aerial remote-sensing measurements of the morphological and morphometric characteristics of the landslides, we assess the influence of thawing ground ice on their propagation style and dynamics. The two mass movements are complex and are similar to rock- and debris-ice avalanches, changing trajectory and exhibiting evidence of transitioning their style of motion from a dry granular mass to a debris flow-like movement via multiple pulses. We infer that the thawing of ground ice together with the entrainment of saturated material provided the extra fluid causing this change in dynamics. The hazardous consequences of permafrost degradation will increasingly affect mountain regions in the future, and ground-ice thaw in steep terrain is a particularly hazardous phenomenon, as it may induce unexpected long-runout failures and can cause slope instability to continue even after the landslide event. Our study expands our knowledge of how landslides develop in unstable ice-cemented deposits and will aid assessment and mitigation of the hazard that they pose in Iceland and other mountainous periglacial areas

The triggering factors of the Móafellshyrna debris slide in northern Iceland: Intense precipitation, earthquake activity and thawing of mountain permafrost

On the 20th September 2012, a large debris slide occurred in the Móafellshyrna Mountain in the Tröllaskagi peninsula, central north Iceland. Our work describes and discusses the relative importance of the three factors that may have contributed to the failure of the slope: intense precipitation, earthquake activity and thawing of ground ice. We use data from weather stations, seismometers, witness reports and field observations to examine these factors. The slide initiated after an unusually warm and dry summer followed by a month of heavy precipitation. Furthermore, the slide occurred after three seismic episodes, whose epicentres were located ~60km NNE of Móafellshyrna Mountain. The main source of material for the slide was ice-rich colluvium perched on a topographic bench. Blocks of ice-cemented colluvium slid and then broke off the frontal part of the talus slope, and the landslide also involved a component of debris slide, which mobilized around 312,000-480,000m(3) (as estimated from field data and aerial images of erosional morphologies). From our analysis we infer that intense precipitation and seismic activity prior to the slide are the main preparatory factors for the slide. The presence of ice-cemented blocks in the slide's deposits leads us to infer that deep thawing of ground ice was likely the final triggering factor. Ice-cemented blocks of debris have been observed in the deposits of two other recent landslides in northern Iceland, in the Torfufell Mountain and the Árnesfjall Mountain. This suggests that discontinuous mountain permafrost is degrading in Iceland, consistent with the decadal trend of increasing atmospheric temperature in Iceland. This study highlights a newly identified hazard in Iceland: landslides as a result of ground ice thaw. Knowledge of the detailed distribution of mountain permafrost in colluvium on the island is poorly constrained and should be a priority for future research in order to identify zones at risk from this hazard