Snow Avalanche Motion and Related Phenomena

Hopfinger, Emil J.

doi:10.1146/annurev.fl.15.010183.000403

Cited by 175 publications

(133 citation statements)

References 43 publications

(47 reference statements)

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“…The maximum pressure is expected to occur for the maximum values in velocity and density. As mentioned by Hopfinger (1983), laboratory experiments show that the velocity inside the avalanche can be 1.5-2.5 times the front velocity, and close to the ground the effective density is larger than the average density, by a factor 2 to 4, in real powder snow avalanches. Therefore, the measured peak pressure can be larger, by a factor of 10, than the pressure calculated from the front velocity and the average velocity.…”

Section: Effect Of the Dammentioning

confidence: 86%

Physical modelling of the interaction between powder avalanches and defence structures

Naaim-Bouvet¹,

Naaïm²,

Bacher³

et al. 2002

Nat. Hazards Earth Syst. Sci.

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Abstract. In order to better understand the interaction between powder snow avalanches and defence structures, we carried out physical experiments on small-scale models. The powder snow avalanche was simulated by a heavy salt solution in a water tank. Quasi two-dimensional and threedimensional experiments were carried out with different catching dam heights. For the reference avalanche, the velocity just behind the nose in the head was greater than the front velocity. For the 2-D configuration, the ratio U max /U front was as high as 1.6, but it depends on the height. For the 3-D configuration, this ratio differed slightly and was even greater (up to 1.8). The vertical velocity rose to 106% of the front velocity for the 3-D simulation and 74% for the 2-D simulation. The reduction in front velocity due to the presence of dams was an increasing function of the dam height. But this reduction depended on topography: dams were more effective on an open slope avalanche (3-D configuration). The ratio U max /U front was an increasing function of the dam's height and reached a value of 1.9. The obstacle led to a reduction in vertical velocity downstream of the vortex zone.

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Section: Effect Of the Dammentioning

confidence: 86%

Physical modelling of the interaction between powder avalanches and defence structures

Naaim-Bouvet¹,

Naaïm²,

Bacher³

et al. 2002

Nat. Hazards Earth Syst. Sci.

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“…£ow velocity (Smith et al, 1994). Snow avalanches have densities of 50^400 kg m 33 (Hop¢nger, 1983). Turbidity currents have densities of V1060^1140 kg m 33 (van Tassel, 1981).…”

Section: Impact By High-momentum £Ows ('Impact Pools')mentioning

confidence: 99%

Occurrence and origin of submarine plunge pools at the base of the US continental slope

et al. 2002

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High-resolution bathymetric data from the New Jersey and Californian continental margins show a marked depression running along parts of the base of the continental slope. Detailed analysis reveals that the depressions are a series of discrete 'plunge pools' with associated downslope topographic ramparts. We have used new bathymetric data to create our own data base (of over 150 examples) and systematically analyse plunge pool morphology and location. Previous observations of plunge pools have been sparse. Plunge pools are up to 1100 m wide and 75 m deep, with a mean diameter of 400 m and a mean depth of 21 m. Plunge pools only occur where there are sharp decreases in slope of more than 4 ‡, and are well developed where changes in slope exceed 15 ‡. We propose plunge pools can be created by two mechanisms. Firstly, they may be due to reduced bed shear stress downstream of hydraulic jumps in submarine sediment-laden density flows that causes the deposition of bedload and the creation of a sediment bar. This bar then defines the downslope margin of a pool. Secondly, the impact of high-momentum sediment-laden density flows can excavate a depression, as has been observed for subaerial snow avalanches. Sediment deposited downslope of these impact pools is very poorly sorted, and partly derived from erosion within the pool. Both mechanisms influence whether turbidity currents are generated from high-density sediment-laden density flows, influence whether depositional flows are channelised, and have implications for base-of-slope facies models. ß

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“…They note the work of Te Chow [1959] on open channel flow that states Vedernikov's criterion that for Froude numbers >2 a "slug flow" regime develops from a dense flow having an unstable surface characterized by surges and turbulent ridges separated by highly agitated regions and that for Froude numbers >3.5 [Henderson, 1966] air entrainment leads to the occurrence of a middle zone, they call "light flow. " Hopfinger [1983] proposed a similar idea that roll waves with strong air intake are regions of turbulences with roller motion and may be the cause of the powder cloud. This and the light flow are probably equivalent to our intermittent frontal region.…”

Section: Introductionmentioning

confidence: 99%

The dynamics of surges in the 3 February 2015 avalanches in Vallée de la Sionne

Köhler¹,

McElwaine

Sovilla³

et al. 2016

JGR Earth Surface

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Five avalanches were artificially released at the Vallée de la Sionne test site in the west of Switzerland on 3 February 2015 and recorded by the GEOphysical flow dynamics using pulsed Doppler radAR Mark 3 radar system. The radar beam penetrates the dilute powder cloud and measures reflections from the underlying denser avalanche features allowing the tracking of the flow at 111 Hz with 0.75 m downslope resolution. The data show that the avalanches contain many internal surges. The large or “major” surges originate from the secondary release of slabs. These slabs can each contain more mass than the initial release, and thus can greatly affect the flow dynamics, by unevenly distributing the mass. The small or “minor” surges appear to be a roll wave‐like instability, and these can greatly influence the front dynamics as they can repeatedly overtake the leading edge. We analyzed the friction acting on the fronts of minor surges using a Voellmy‐like, simple one‐dimensional model with frictional resistance and velocity‐squared drag. This model fits the data of the overall velocity, but it cannot capture the dynamics and especially the slowing of the minor surges, which requires dramatically varying effective friction. Our findings suggest that current avalanche models based on Voellmy‐like friction laws do not accurately describe the physics of the intermittent frontal region of large mixed avalanches. We suggest that these data can only be explained by changes in the snow surface, such as the entrainment of the upper snow layers and the smoothing by earlier flow fronts.

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Snow Avalanche Motion and Related Phenomena

Cited by 175 publications

References 43 publications

Physical modelling of the interaction between powder avalanches and defence structures

Physical modelling of the interaction between powder avalanches and defence structures

Occurrence and origin of submarine plunge pools at the base of the US continental slope

The dynamics of surges in the 3 February 2015 avalanches in Vallée de la Sionne

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