Drowning unconformities are stratigraphic key surfaces in the history of carbonate platforms. They mostly consist in the deposition of deep marine facies on top of shallow marine limestones. Although ...large-scale depositional geometries mimic lowstand systems track architecture, these sedimentary turnovers are developed in relation with major sea level rise, inducing an increase in the rate of creation of accommodation space that outpaces the capacity of carbonate to keep up. This so-called paradox of carbonate platform drowning implies that parameters other than purely eustatic fluctuations are involved in the demise of shallow marine ecosystems. Worldwide and at different times during Earth history, in-depth studies of drowning unconformities revealed that changes in nutrient input, clastic delivery, temperature, or a combination of them may be responsible for a decrease in light penetration in the water column and the progressive suffocation and poisoning of photosynthetic carbonate producers. The examination of such case examples from various stratigraphic intervals and palaeogeographical settings thus helps in identifying and hierarchizing potential triggering mechanisms for drowning unconformities.
This is complemented by new data from Early Cretaceous successions from the Helvetic Alps. During this time period, the Helvetic carbonate platform developed along the northern Tethyan margin using both photozoan and heterozoan communities. Phases of healthy production were interrupted by several drowning episodes. The latter are marked in the sedimentary record by condensation and associated phosphogenesis and glauconitisation. From the earliest Valanginian to the early to late Barremian, three drowning unconformities reflect the intermittent installation of a more humid climate and subsequent enhanced trophic conditions, which first induced a switch from photozoan to heterozoan communities and then to long-lasting drowning phases. The latter encompass several sea level rise and fall cycles, and may be linked to strengthened upwelling currents. With the return to more oligotrophic conditions during the late Barremian, photozoan, Urgonian-type communities took up again. Their development has been abruptly stopped at the end of the early Aptian by a major emersion phase. The subsequent drowning is documented in various peritethyan areas. This initial crisis is followed by three other drowning phases that ultimately led to the replacement of shallow ecosystems by a deeper marine sedimentation in the Cenomanian. This long-term trend in the evolution of the Helvetic carbonate platform and of other peritethyan ecosystems may have been driven by more global phenomena. In particular, the progressive opening of the northern and equatorial Atlantic may have impacted sea level by creating new oceanic basins. The emplacement of submarine volcanic plateaus may have triggered sea level rise and fertilized deep oceanic waters through hydrothermal processes. Drowning unconformities thus record the interplay of local with long-term processes, and constitute regional sedimentary archives of global phenomena.
•The sequence stratigraphic significance of drowning unconformities is discussed.•Changes in palaeoenvironmental conditions often acted as triggering mechanisms.•The Helvetic platform experienced drowning unconformities during the Early Cretaceous.•A link between drowning episodes and global perturbations is postulated.
This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under ...investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001–2050 and 2051–2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50 mm) and durations (1, 2 or 3 days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21
st
century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21
st
century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3 days.
Since the late 1960s it became clear that a more sustainable protection of people and property from the negative impacts of natural hazards will require a more balanced use of structural and ...non-structural measures, such as land-use planning and ecosystem-based solutions for disaster risk reduction, also called Eco-DRR. The most prominent example of Eco-DRR in mountainous regions are forests that protect people, settlements and infrastructures against gravitational natural hazards such as avalanches, landslides and hazards related to mountain torrents. The goal of this paper is to provide an overview on the influence of forests on risks induced by natural hazards and the associated challenges and uncertainties concerning risk analysis. Approaches from natural hazard risk are presented, along with recent results from forest research, thereby offering new ways to integrate forests into risk analysis. We discuss the potential effects of forests on the three important hazard components of the risk concept, namely the onset probability, the propagation probability and the intensity, and propose a set of guiding principles for integrating forests into quantitative risk assessment (QRA) for natural hazards. Our focus thereby lies on snow avalanches, rockfalls, floods, landslides, and debris flows. This review shows that existing methods and models for assessing forest effects on natural hazards suffice for integrating forests into QRA. However, they are mostly limited to the stand- or slope-scale, and further efforts are therefore needed to upscale these approaches to a regional level, and account for uncertainties related to forest effects and natural dynamics. Such a dynamic, rather than a static assessment of risk will finally allow for planning and implementing intelligent combinations of Eco-DRR and technical protection measures.
In this paper, we describe the investigations and actions taken to reduce risk and prevent casualties from a catastrophic 210,000 m
3
rockslope failure, which occurred near the village of Preonzo in ...the Swiss Alps on May 15, 2012. We describe the geological predisposition and displacement history before and during the accelerated creep stage as well as the development and operation of an efficient early warning system. The failure of May 15, 2012, occurred from a large and retrogressive instability in gneisses and amphibolites with a total volume of about 350,000 m
3
, which formed an alpine meadow 1250 m above the valley floor. About 140,000 m
3
of unstable rock mass remained in place and might collapse partially or completely in the future. The instability showed clearly visible signs of movements along a tension crack since 1989 and accelerated creep with significant hydromechanical forcing since about 2006. Because the active rockslide at Preonzo threatened a large industrial facility and important transport routes located directly at the toe of the slope, an early warning system was installed in 2010. The thresholds for prealarm, general public alarm, and evacuation were derived from crack meter and total station monitoring data covering a period of about 10 years, supplemented with information from past failure events with similar predisposition. These thresholds were successfully applied to evacuate the industrial facility and to close important roads a few days before the catastrophic slope failure of May 15, 2012. The rock slope failure occurred in two events, exposing a compound rupture plane dipping 42° and generating deposits in the midslope portion with a travel angle of 39°. Three hours after the second rockslide, the fresh deposits became reactivated in a devastating debris avalanche that reached the foot of the slope but did not destroy any infrastructure. The final run-out distance of this combined rock collapse–debris avalanche corresponded to the predictions made in the year 2004.
What the bubble knows Langenegger, T.; Vachon, D.; Donis, D. ...
Limnology and oceanography,
07/2019, Letnik:
64, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Atmospheric methane (CH₄) concentrations have more than doubled in the past ~ 250 yr, although the sources of this potent greenhouse gas remain poorly constrained. Freshwaters contribute ~ 20% of ...natural CH₄ emissions, about half attributed to ebullition. Estimates remain uncertain as ebullition is stochastic, making measurements difficult, time consuming, and costly with current methods (e.g., floating chambers, funnel gas traps, and hydroacoustics). We present a novel approach to quantify basin-wide hypolimnetic CH₄ fluxes at the sediment level based on measurements of bubble gas content and modeling of dissolved pore-water gases. We show that the relative ebullition flux pathway can be resolved by knowledge of only bubble gas content. As sediment CH₄ production, diffusion, and ebullition are interrelated, the addition of a second observation allows closing the entire sediment CH₄ balance. Such measurements could include bubble formation depth, sediment diffusive fluxes, ebullition, sediment CH₄ production, or the hypolimnetic CH₄ mass balance. The measurement of bubble gas content is particularly useful for identifying local ebullitive hotspots and integrating spatial heterogeneity of CH₄ fluxes. Our results further revealed the crucial effect of water column depth, production rates, and hypolimnetic dissolved CH₄ concentrations on sediment CH₄ dynamics. Although we apply the model to cohesive sediments in an anoxic hypolimnion, the model can be applied to shallow, oxic settings by altering the CH₄ production rate curve to account for oxidation. Utilizing our approach will provide a deeper understanding of in-lake CH₄ budgets, and thus improve CH₄ emission estimates from inland freshwaters at the regional and global scales.
States without former colonies, it has been argued, were intensely involved in colonial practices. This anthology looks at Switzerland, which, by its very strong economic involvements with ...colonialism, its doctrine of neutrality, and its transnationally entangled scientific community, constitutes a perfect case in point.
In this volume Sabina Widmer analyses neutral Switzerland’s foreign policy in Angola, Mozambique, Ethiopia, and Somalia during the armed conflicts and regime changes of the late 1960s and 1970s, in a ...context of global Cold War and decolonisation.; Readership: All interested in Swiss foreign policy after 1945, neutrality during the Cold War, Africa in the Cold War, and European politics towards Africa.
This paper presents a short history of the appraisal of laser scanner technologies in geosciences used for imaging relief by high-resolution digital elevation models (HRDEMs) or 3D models. A general ...overview of light detection and ranging (LIDAR) techniques applied to landslides is given, followed by a review of different applications of LIDAR for landslide, rockfall and debris-flow. These applications are classified as: (1) Detection and characterization of mass movements; (2) Hazard assessment and susceptibility mapping; (3) Modelling; (4) Monitoring. This review emphasizes how LIDAR-derived HRDEMs can be used to investigate any type of landslides. It is clear that such HRDEMs are not yet a common tool for landslides investigations, but this technique has opened new domains of applications that still have to be developed.
The short chronicle Jussie, Jeanne de; Klaus, Carrie F
2006., 2007, 2006
eBook
Jeanne de Jussie (1503–61) experienced the Protestant Reformation from within the walls of the Convent of Saint Clare in Geneva. In her impassioned and engaging Short Chronicle, she offers a singular ...account of the Reformation, reporting not only on the larger clashes between Protestants and Catholics but also on events in her convent—devious city councilmen who lied to trusting nuns, lecherous soldiers who tried to kiss them, and iconoclastic intruders who smashed statues and burned paintings. Throughout her tale, Jussie highlights women’s roles on both sides of the conflict, from the Reformed women who came to her convent in an attempt to convert the nuns to the Catholic women who ransacked the shop of a Reformed apothecary. Above all, she stresses the Poor Clares’ faithfulness and the good men and women who came to them in their time of need, ending her story with the nuns’ arduous journey by foot from Reformed Geneva to Catholic Annecy. First published in French in 1611, Jussie’s Short Chronicle is translated here for an English-speaking audience for the first time, providing a fresh perspective on struggles for religious and political power in sixteenth-century Geneva and a rare glimpse at early modern monastic life.
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