scholarly journals Brief communication: Weak control of snow avalanche deposit volumes by avalanche path morphology

2021 ◽  
Vol 15 (10) ◽  
pp. 4845-4852
Author(s):  
Hippolyte Kern ◽  
Nicolas Eckert ◽  
Vincent Jomelli ◽  
Delphine Grancher ◽  
Michael Deschatres ◽  
...  
Keyword(s):  
Snow Avalanche ◽  
Statistical Techniques ◽  
Snow Avalanches ◽  
Climate Conditions ◽  
French Alps ◽  
Non Linear ◽  
Genesis Of Deposit ◽  
Mechanical Thresholds ◽  
Linear Nature

Abstract. Snow avalanches are a major component of the mountain cryosphere, but little is known about the factors controlling the variability of their deposit volumes. This study investigates the influence of avalanche path morphology on ca. 1500 deposit volumes recorded between 2003 and 2018 in 77 snow avalanche paths of the French Alps. Different statistical techniques show a slight but significant link between deposit volumes and path mean elevation and orientation, with contrasted patterns between winter and spring seasons. The limited and partially non-linear nature of this control may result from the combined influence on the genesis of deposit volumes of mean path activity, climate conditions, and mechanical thresholds determining avalanche release.

scholarly journals Brief communication: Weak control of snow avalanche deposit volumes by paths morphological characteristics

2021 ◽  
Author(s):  
Hippolyte Kern ◽  
Nicolas Eckert ◽  
Vincent Jomelli ◽  
Delphine Grancher ◽  
Michael Deschatres ◽  
...  
Keyword(s):  
Morphological Characteristics ◽  
Snow Avalanche ◽  
Statistical Techniques ◽  
Snow Avalanches ◽  
Climate Conditions ◽  
French Alps ◽  
Non Linear ◽  
Genesis Of Deposit ◽  
Mechanical Thresholds ◽  
Linear Nature

Abstract. Snow avalanches are a major component of the mountain cryosphere, but little is known about the factors controlling the variability of their deposit volumes. This study investigates the influence of morphological characteristics on c. 1500 deposit volumes recorded between 2003 and 2018 in 77 snow avalanche paths of the French Alps. Different statistical techniques show a slight but significant link between deposit volumes and path mean elevation and orientation, with contrasted patterns between winter and spring seasons. The weakness, partially non-linear nature of this control may result from the combined influence on the genesis of deposit volumes of mean path activity, climate conditions and mechanical thresholds determining avalanche release.

Impacts of land-cover changes on dendrogeomorphic reconstructions of snow avalanches: Insights from the Queyras massif (French Alps)

2020 ◽  
Author(s):  
Adrien Favillier ◽  
Robin Mainieri ◽  
Jérôme Lopez-Saez ◽  
Mélanie Saulnier ◽  
Nicolas Eckert ◽  
...  
Keyword(s):  
Global Warming ◽  
Snow Cover ◽  
Tree Ring ◽  
Environmental Changes ◽  
Mass Movement ◽  
Sudden Change ◽  
Snow Avalanche ◽  
High Mountain ◽  
Snow Avalanches ◽  
French Alps

<p>In the course of the 20th century, high-mountain regions, such as the Alps, have experienced a significant warming with temperature increase twice as much as the global average. Such warming strongly alters the cryosphere components. It induces, for example, a shift from solid to liquid precipitation, more frequent and more intense snowmelt phases or a strong decrease in the amount and duration of snow cover, especially at the location of the snow-rain transition. Such changes in snow cover characteristics are expected to induce changes in spontaneous avalanche activity.</p><p>On forested stands, dendrogeomorphic analyses provide long and continuous chronologies of snow avalanche events and can thus contribute to the detection of trends potentially related to climate change. However, the non-stationarities found in tree-ring based chronologies of snow avalanches may also be related to socio-environmental changes. In this context, based on the latest the latest developments in dendrogeomorphology, we reconstructed the snow avalanche activity for 6 contiguous paths located in the Grand Bois de Souliers slope (Queyras massif, French Alps) with the aim to :</p><ol><li>Detect and illustrate such confounding effects;</li> <li>Disentangle the trends inherent to tree-ring approaches from real fluctuations in avalanche activity.</li> </ol><p>The resulting reconstruction covers the period 1750-2016 and evidences two clearly different trends: on the three southern avalanche paths, a sharp increase in the frequency of reconstructed events is observed since the 1970s. The distribution of tree ages, in combination with old topographic maps, allows an attribution of this non-stationarity to the destruction of a large part of the forest stand in the 1910-20s, presumably related to a devastating avalanche event. This extreme event induced a sudden change in the capability of newly colonizing trees to yield dendrogeomorphic records as information on previous or subsequent events has been removed. By contrast, on the three northern paths, snow avalanche activity is truly characterized by a strong reduction since the 1930s related to the progressive afforestation of the paths since the mid-18<sup>th</sup> century and to the colonization of the release areas since World War 2. Even if we cannot rule out the possibility that global warming may have played a certain, yet likely minor, role in the evolution of these avalanche-forest ecosystem, we conclude that the contrasted evolutions observed between the avalanche paths can, above all, be explained by socio-environmental factors (e.g., forest and grazing management) during the 18<sup>th</sup> century that have gained in importance by the rural exodus and the abatement of pastoral practices during the 20<sup>th</sup> century. In that sense, our results evidence quite clearly the crucial need for future studies aimed at detecting changes in mass-movement activity from tree-ring analyses to systematically interpret trends in activity considering interrelations between forest evolution, global warming, social practices and process activity itself.</p>

Un-Shocked High Amplitude Standing Waves in Wave-Shaped Resonators

2012 ◽  
Author(s):  
Dion Savio Antao ◽  
Bakhtier Farouk
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Ambient Pressure ◽  
Standing Waves ◽  
High Amplitude ◽  
Prime Mover ◽  
Non Linear ◽  
Resonator System ◽  
Cylindrical Resonators ◽  
Linear Nature

A numerical study of non-linear, high amplitude standing waves in non-cylindrical circular resonators is reported here. These waves are shock-less and can generate peak acoustic overpressures that can exceed the ambient pressure by three/four times its nominal value. A high fidelity compressible computational fluid dynamic model is used to simulate the phenomena in cylindrical and arbitrarily shaped axisymmetric resonators. A right circular cylinder and frustum of cone are the two geometries studied. The model is validated using past numerical and experimental results of standing waves in cylindrical resonators. The non-linear nature of the harmonic response of the frustum of cone resonator system is investigated for two different working fluids (carbon dioxide and argon) operating at various values of piston amplitude. The high amplitude non-linear oscillations demonstrated can be used as a prime mover in a variety of applications including thermoacoustic cryocooling.

scholarly journals The mechanical origin of snow avalanche dynamics and flow regime transitions

2020 ◽  
Author(s):  
Xingyue Li ◽  
Betty Sovilla ◽  
Chenfanfu Jiang ◽  
Johan Gaume
Keyword(s):  
Flow Velocity ◽  
Alpha Angle ◽  
Maximum Flow ◽  
Flow Regimes ◽  
Snow Avalanche ◽  
Snow Avalanches ◽  
Deposition Zone ◽  
Avalanche Dynamics ◽  
Maximum Flow Velocity ◽  
Deposit Height

Abstract. Snow avalanches cause fatalities and economic damages. Key to their mitigation entails the understanding of snow avalanche dynamics. This study investigates the dynamic behaviors of snow avalanches, using the Material Point Method (MPM) and an elastoplastic constitutive law for porous cohesive materials. By virtue of the hybrid Eulerian-Lagrangian nature of MPM, we can handle processes involving large deformations, collisions and fractures. Meanwhile, the elastoplastic model enables us to capture the mixed-mode failure of snow, including tensile, shear and compressive failure. Using the proposed numerical approach, distinct behaviors of snow avalanches, from fluid-like to solid-like, are examined with varied snow mechanical properties. In particular, four flow regimes reported from real observations are identified, namely, cold dense, warm shear, warm plug and sliding slab regimes. Moreover, notable surges and roll-waves are observed peculiarly for flows in transition from cold dense to warm shear regimes. Each of the flow regimes shows unique flow characteristics in terms of the evolution of the avalanche front, the free surface shape, and the vertical velocity profile. We further explore the influence of slope geometry on the behaviors of snow avalanches, including the effect of slope angle and path length on the maximum flow velocity, the $\\alpha$ angle and the deposit height. Unified trends are obtained between the normalized maximum flow velocity and the scaled $\\alpha$ angle as well as the scaled deposit height, reflecting analogous rules with different geometry conditions of the slope. It is found the maximum flow velocity is mainly controlled by the friction between the bed and the flow, the geometry of the slope, and the snow properties. In addition to the flow behavior before reaching the deposition zone, which has long been regarded as the key factor governing the $\\alpha$ angle, we reveal the crucial effect of the stopping behavior in the deposition zone. Furthermore, our MPM model is benchmarked with simulations of real snow avalanches. The evolution of the avalanche front position and velocity from the MPM modeling shows reasonable agreement with the measurement data from literature. The MPM approach serves as a novel and promising tool to offer systematic and quantitative analysis for mitigation of gravitational hazards like snow avalanches.

scholarly journals Is our perception of the spread of COVID-19 inherently inaccurate?

2021 ◽  
Author(s):  
Alexander Maier
Keyword(s):  
Decision Making ◽  
Subjective Perception ◽  
Logarithmic Function ◽  
Original Formulation ◽  
Global Crisis ◽  
New Information ◽  
The World ◽  
Non Linear ◽  
The Future ◽  
Linear Nature

One of the most fundamental insights into the nature of our subjective perception of the world around us is that it is not veridical. In other words, we tend to not perceive information about the world around us accurately. Instead, our brains interpret new information through a host of innate and learned mechanisms that can introduce bias and distortions One of the best studied mechanisms that guide – and distort – our perception is the psychophysical Weber-Fechner law. According to this empirically derived, mathematically formulated law we tend to put more emphasis on smaller deviations in size while underestimating larger changes. The original formulation of the Weber-Fechner law takes the shape of a logarithmic function and is commonly applied to somatosensory perception such as the weight of an object. However, later work showed that the Weber-Fechner law can be generalized and describe a large variety of perceived changes in magnitude that even go beyond the sensory domain. Here we investigate the hypothesis that our perception of data associated with the spread of COVID-19 and similar pandemics is governed by the same psychophysical laws. Based on several recently published studies, we demonstrate that the Weber-Fechner law can be shown to directly affect the decision-making of officials in response to this global crisis as well as the greater public at large. We discuss how heightened awareness of the non-linear nature of subjective perception could help alleviate problematic judgements in similar situations in the future.

scholarly journals Mediating the Message of Action Research

2011 ◽  
Vol 7 (2) ◽  
Author(s):  
Terry Sefton ◽  
Sheila Windle
Keyword(s):  
Action Research ◽  
Collaborative Action Research ◽  
Data Sources ◽  
Collaborative Action ◽  
Teacher Researchers ◽  
Non Linear ◽  
Context Specific ◽  
Linear Nature

In this paper we argue that a multimedia composition of various data sources is an ideal and appropriate medium for conveying the complex, context-specific, teacher-directed, multi-layered, non-linear nature of collaborative action research (CAR). This compilation also expresses the main outcomes of eight CAR studies conducted by eight teams of teacher-researchers in southwestern Ontario during 2007-2008.

A numerical approach for simulating two-dimensional dense-snow avalanches in global coordinate systems

2021 ◽  
Author(s):  
Daniel Zugliani ◽  
Giorgio Rosatti ◽  
Stefania Sansone
Keyword(s):  
Coordinate System ◽  
Finite Volume ◽  
Reference System ◽  
Source Term ◽  
Numerical Approach ◽  
The Other ◽  
Snow Avalanche ◽  
Two Dimensional ◽  
Snow Avalanches ◽  
Avalanche Models

<p>Snow avalanche models are commonly based on a continuum fluid scheme, on the assumption of shallow flow in the direction normal to the bed, on a depth-averaged description of the flow quantities and on different assumptions concerning the velocity profile, the friction law, and the pressure in the flow direction (see Bartelt et al, 1999, Barbolini et al., 2000, for an overview). The coordinate reference system is commonly local, i.e., for each point of the domain, one axis is normal to the bed while the other two axes lay in a tangent plane. When the bed is vertical and the flow is not aligned with the steepest direction (e.g., in case of a side wall), the flow depth is no longer defined considering the normal direction and the model based on the local coordinate system is no longer valid. In near-vertical conditions, numerical problems can be expected.</p><p>Another critical point, for numerical models based on finite volume schemes and Godunov fluxes, is the accurate treatment of the source term in case of no-motion conditions (persistence, starting and stopping of the flow) due to the presence of velocity-independent, Coulomb-type terms in the bed shear stress. </p><p>In this work, we provide a numerical approach for a Voellmy-fluid based model, able to overcome the limits depicted above, to accurately simulate analytical solutions and to give reliable solutions in other cases (Zugliani & Rosatti, 2021). Firstly, differently from the other literature models, the chosen coordinate reference system is global (an axis opposite the gravity vector and the other two orthogonal axes lay in the horizontal plane) and therefore, the relevant mass and momentum equations have been derived accordingly. Secondly, these equations have been discretized by using a finite volume method on a Cartesian square grid where the Godunov fluxes has been evaluated by mean of a modified DOT scheme (Zugliani & Rosatti, 2016) while source terms in conditions of motion have been discretized by using an implicit operator-splitting technique. Finally, a specific algorithm has been derived to deal with the source term to determine the no-motion conditions.  Several test cases assess the capabilities of the proposed approach.</p><p> </p><p><strong>References:</strong></p><p>Barbolini, M., Gruber, U., Keylock, C.J., Naaim, M., Savi, F. (2000), <em>Application of statistical and hydraulic-continuum dense-snow avalanche models to five real European sites.</em> Cold Regions Science and Tech. 31, 133–149.</p><p>Bartelt, P., Salm, B., Gruber, U. (1999), <em>Calculating dense-snow avalanche runout using a voellmy-fluid model with active/passive longitudinal straining.</em> Journal of Glaciology 45, 242-254.</p><p>Zugliani D., Rosatti G. (2021), <em>Accurate modeling of two-dimensional dense snow avalanches in global coordinate system: the TRENT2D<sup>❄</sup> approach. </em>Paper under review.</p><p>Zugliani, D., Rosatti, G. (2016), <em>A new Osher Riemann solver for shallow water flow over fixed or mobile bed</em>, Proceedings of the 4th European Congress of the IAHR, pp. 707–713.</p>

scholarly journals Scale Modeling of Snow–Avalanche Impact on Structures

1980 ◽  
Vol 26 (94) ◽  
pp. 189-196
Author(s):  
T. E. Lang ◽  
J.D. Dent
Keyword(s):  
Froude Number ◽  
Computer Modeling ◽  
Snow Avalanche ◽  
Small Scale ◽  
Snow Avalanches ◽  
Scale Modeling ◽  
Impact Processes ◽  
Model Fluid ◽  
Impact Predictions

AbstractSmall–scale modeling of flow and impact of snow avalanches is demonstrated to be both feasible and accurate. Geometric, kinematic, and force variables are scaled correctly under equivalence of Froude number between prototype and model using sifted snow as the model fluid. Physical and computer–simulated impact processes show correspondence, so that computer modeling is demonstrated to be a viable tool in flow and impact predictions.

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