1,721,002 research outputs found
Characterization of landslide dams in the San Juan province (Argentina)
Get PDFRiver blockages caused by landslide deposition are common phenomena in active mountain chains, influencing erosion-sedimentation patterns and acting as primary and secondary hazards. Regional scale analyses regarding their spatial distribution and morphometry allow establishing boundary conditions for their occurrence and stability, and determine differences among regions with different landscape and climatic conditions. Owing to the combination of endogenous and exogenous factors, landslide dams are frequent phenomena in the Andes. In the Argentinean NW and the Patagonian Andes, previous studies showed that stability of landslide dams determined by morphometric parameters generally matched satisfactorily with dam behavior, with some exceptions in which climatic component played an important role in dam longevity. Aiming to expand the knowledge of landslide dams in the Argentinean Andes, in this work we analyzed the stability of rock avalanche dams in the Pampeam flat slab subduction zone. In the study area, mountain dynamics creates suitable conditions for the occurrence of 34 rock avalanches with volumes up to 0.3 km3. They developed in deeply carved valleys (Cordillera) and Inter-thrust valleys (Precordillera). 22 impoundments of rivers resulted from channelized rock avalanches with long runouts (4-10 km) that blocked tributaries rivers, but most of them by rock avalanches that filled the valley bottom, with run up in the opposite slope and limited movement parallel to the valley axis. Most of the dams breached in unknown times, except for the last event that occurred on November 12th 2005. The quantification of morphometric parameters and contributing areas indicates the existence of dams with dimensionless blockage index above 2.75 (stable domain) and below 3.08 (instable domain). The Los Erizos dam in our study area and the Barrancas dam in the Patagonian Andes show that besides morphometric parameters, climatic conditions are decisive. Stable landslide dams lasting for millennia can collapse suddenly due to anomalous weather conditions, and unstable dams can have a higher longevity depending on the season controlling the inflow into the lake.Fil: Penna, Ivanna Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Longchamp, Celine. Universite de Lausanne; SuizaFil: Derron, Marc Henri. Universite de Lausanne; SuizaFil: Jaboyedoff, Michel. Universite de Lausanne; SuizaEGU General Assembly 2013AustriaEuropean Geosciences Unio
Vulnerability Assessment of Buildings Exposed to Deep-seated Landslide Activity in the Joshimath town of Chamoli, Uttarakhand, India
No full textUrban risks and resilience in the rwandan context
Get PDFThe rapid urbanization in Rwanda, a country with a disrupted habitat culture has led to a congestion of the capital, which concentrates all services. This has, among other things, a particular form of nature and impacts of natural hazards.
Within the context of the natural hazards of Rwanda, we address the problems of the natural hazards due to rains in a watershed of Kigali (natural hazards analysis database and GIS data problematics) and Ruhengeri. Debris flows / landslides modelling are performed including source areas identification and potential propagation zones, with regard to the built-up areas and available maps. This is integrated in a conceptual multi-hazards and complex natural systems for the two cities. It demonstrates the highly complex situation at risk and how people were resilient before "modernity". This leads us to develop a plan dedicated to the communication of sustainable solutions, to make solutions possible
Analysis of rock wall retreat from Alpine to Subalpine environments using remote sensing monitoring with different temporal resolutions under local microclimate variation
No full textRockfall-induced retreat of rock walls plays a critical role in shaping landforms across diverse geographical environments. These events pose significant threats to infrastructure, pedestrian safety, and residential areas, causing considerable damage to both human settlements and natural habitats located below these rock walls. In alpine environments, factors such as accelerating glacier retreat and permafrost degradation driven by global warming are expected to increase rockfall activity, thus accelerating the retreat rate of rock walls. Similarly, in coastal settings, localized intense extreme climatic events, such as heavy storms (resulting in strong wave action) and intense precipitation under climate change, increase the frequency of rock wall collapses at cliff bases, leading to accelerated cliff retreat. However, the dynamics of rock walls in sub-alpine environments have received less attention compared to those in high alpine regions. The lack of research involving short-to-long term and detailed rockfall data at both the rock wall scale and regional level limits our understanding of potential trends in increasing rockfall activity driven by global warming.
To investigate the retreat of rock walls caused by rockfalls and the associated risks across alpine to sub-alpine environments under climate change, this doctoral dissertation first focuses on rock wall retreat (a historical rockslide scar) caused by rockfalls and defines potential failure scenarios in an alpine environment affected by accelerating global warming (Brenva Spur, Mont Blanc Massif, Italy). Using helicopter-borne Structure-from-Motion (SfM) photogrammetry over a five-year period, a comprehensive rockfall source database was established following a major sliding event in 2016. This database, combined with data from the largest historical rockslide events, facilitated the evaluation of the volume-frequency relationship and the estimation of rock wall retreat rates. The volume-frequency relationship, based on the rock failure inventory, was fitted using a power-law distribution while considering relevant uncertainties. By employing structural analysis and the Slope Local Base Level (SLBL) approach, seven potential future rock failure scenarios were delineated and used for risk assessment.
The second part of the thesis shifts focus to the retreat of a rock wall (a lateral scarp of a historical landslide) caused by rockfalls in a sub-alpine environment. This section explores whether local extreme climatic events, such as intense rainfall and heatwaves, affect rockfall activity in a manner similar to that observed in alpine environments under global warming. A molasse rock wall in a Swiss sub-alpine mountain was selected for monthly remote sensing surveys using drone-borne SfM photogrammetry and terrestrial laser scanning (TLS). These surveys enabled the establishment of a detailed rockfall database, capturing frequency, volume, and location information for each survey period. Concurrently, meteorological data, including rainfall, snowmelt, evapotranspiration (ET), and air temperature, were collected from nearby weather stations to analyze the effects of external environmental factors and/or local climate variations on the occurrences of rock detachments.
Characterized by interlayered soft (marl) and hard (sandstone) rocks, the La Cornalle rock wall exhibited differential erosion features, underscoring the significant role of faster retreat of soft rock layers in the overall rock wall retreat process. Thus, in the third part, to specifically examine small-scale detachments and micro-crack activity in the soft marl layers using multi scale observation methods, 26 hours of short-distance TLS monitoring at two-hour intervals were conducted during late winter (March). These efforts were supplemented with 20-minute interval Infrared Thermography (IRT) for rock surface temperature monitoring, solar radiation measurements, and hourly digital microscope-based micro-crack displacement monitoring. The comprehensive results from these multi-scale observation methods provided insights into the spatiotemporal distribution of small detachments and micro-crack movements on the rock wall face.
The findings from these three parts reveal that local climate anomalies significantly influence rockfall trends and related rock wall retreat rates in both alpine and sub-alpine environments. The rapid surface permafrost degradation during the 2015 summer heatwave likely altered rock wall retreat of Brenva Spur by triggering numerous superficial rock detachments with months or years of delay, as evidenced by two rockslides in 2016 and the highest retreat rate observed between 2017 and 2018. Estimations of return periods for defined failure scenarios in the future are subject to large uncertainties, particularly under ongoing global warming. In sub-alpine regions, rockfall activity in molasse rock walls is strongly predisposed by rock wall structure and lithology. Temporal variations in rockfall events and retreat rates are closely correlated with local changing meteorological conditions. Rockfall events were more frequent during rainy periods, such as the winter and humid spring and summer of 2021, while activity diminished during the extremely dry summer of 2022 (characterized by less rainfall and high ET). A marked increase in rockfall was observed during transitions from warm drought to cold humid conditions (dry-wet), indicating that local climate anomalies can significantly influence rockfall dynamics in this sub-alpine setting.
Daily observations of marl layers within the rock wall highlight the role of thermal weathering in driving micro-crack displacement and subsequent small-scale detachments (with volume less than 0.001 m3) of soft rock. Repeated daily temperature fluctuations (cooling-heating) and variations in solar radiation exacerbate rock mass degradation and small-scale debris flaking. The primary degradation mechanism involves tensile stress from thermal expansion and contraction, alongside the expansion effects of swelling minerals within the marl. However, the latter played a lesser role during the monitoring period, as the observations were conducted in clear and non-rainy weather conditions.
In summary, comprehensive monitoring of rock wall retreat using SfM photogrammetry, TLS, IRT, and digital microscopy, integrated with external environmental variables, demonstrates that local extreme climate anomalies substantially influence rockfall frequency in both alpine and sub-alpine environments. Unexpected extreme weather events challenge the ability to predict and assess rockfall hazards accurately, especially under ongoing climate change. For soft rock, the degradation caused by thermal weathering is crucial, as it promotes debris flaking and can lead to high-frequency, large-scale rockfall events (e.g., the failure of sandstone overhangs) over long periods
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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