A Study on High-Speed Avalanches in the Kurobe Canyon, Japan

Shimizu, Hiromu; Huzioka, Tosio; Akitaya, Eizi; Narita, Hirokazu; Nakagawa, Masayuki; Kawada, Kunio

doi:10.1017/s0022143000010686

Cited by 16 publications

(8 citation statements)

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“…However, in the frontal vortex of the suspension layer, the uplift velocity is similar to the front velocity and should be sufficient to keep large particles in the air for a short while and to transport small particles to the back of the vortex. The transport competence of powder-snow avalanches is demonstrated by the accidents mentioned by Shimizu et al [2] as well as credible reports of persons who were transported above ground over distances of tens of meters in the suspension layer [61].…”

Section: Aerodynamic Forces In the Head Of The Suspension Layermentioning

confidence: 99%

“…The term "powder-snow avalanche" (PSA) is variably used for only the suspension layer or for mixed avalanches. Several avalanche experiments from the 1970s and 1980s [1][2][3][4] indicated that there may be an additional, intermediate-density flow regime. Norem [5] termed it "saltation" in analogy with the three regimes recognized in drifting snow (reptation, saltation, and suspension), but we will call it "fluidized" as this seems to better capture the physical processes at work.…”

Section: Introductionmentioning

confidence: 99%

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Inferences on Mixed Snow Avalanches from Field Observations

Issler

Gauer

Schaer³

et al. 2019

Geosciences

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Observations of the deposits, flow marks, and damages of three mixed-snow avalanches of widely different size were analyzed with regard to flow regimes, velocities, pressures, densities, flow depths, erosion modes, and mass balance. Three deposit types of different density and granulometry could be clearly discerned in these avalanches. They are attributed to dense, fluidized, and suspension flow regimes, respectively. Combining observations, we estimated the density in the fluidized layer as 35–100 kg m − 3 , in good agreement with inferences from pressure measurements. Upper bounds for the suspension layer density, arising from the run-up height, velocity, and damage pattern, are about 5 kg m − 3 at the valley bottom. An approximate momentum balance of the dense layer suggests that the snow cover was eroded to considerable depth, but only partly entrained into the flow proper. The suspension layer had largely lost its erosive power at the point where it separated from the denser parts of the avalanche. Our estimates shed doubt on collisions between snow particles and aerodynamic forces at the head of the avalanche as sole mechanisms for creating and upholding the fluidized layer. We conjecture that the drag from air escaping from the snow cover as it is being compressed by the overriding avalanche could supply the missing lift force.

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Section: Aerodynamic Forces In the Head Of The Suspension Layermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Inferences on Mixed Snow Avalanches from Field Observations

Issler

Gauer

Schaer³

et al. 2019

Geosciences

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“…If correct, we might expect the presence of snow particles would decrease the magnitude of static pressure depression resulting in underestimate of the flow velocity. In fact, Shimizu et al [1980], who carried out measurements in the same valley in 1977, reported that atmospheric pressure gauges often detected small pressure increase after a decrease of several hundred pascals.…”

Section: 2mentioning

confidence: 99%

Velocity distribution in snow avalanches

Nishimura¹,

Ito²

1997

J. Geophys. Res.

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Abstract. In order to investigate the detailed structure of snow avalanches, we have made snow flow experiments at the Miyanomori ski jump in Sapporo and systematic observations in the Shiai-dani, Kurobe Canyon. In the winter of 1995-1996, a new device to measure static pressures was used to estimate velocities in the snow cloud that develops above the flowing layer of avalanches. Measurements during a large avalanche in the Shiai-dani which damaged and destroyed some instruments indicate velocities increased rapidly to more than 50 m/s soon after the front. Velocities decreased gradually in the following 10 s. Velocities of the lower flowing layer were also calculated by differencing measurement of impact pressure. Both recordings in the snow cloud and in the flowing layer changed with a similar trend and suggest a close interaction between the two layers. In addition, the velocity showed a periodic change. Power spectrum analysis of the impact pressure and the static pressure depression showed a strong peak at a frequency between 4 and 6 Hz, which might imply the existence of either ordered structure or a series of surges in the flow. ,xp = pu where p is the density of the air (see Figure 1). However, the diameter (0.01 m) and the length (40 m) of piezometer tube substantially affect equation (1). Wind tunnel experiments were performed to calculate the exact relation, and the method of least squares was used to calculate the empirical equation

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“…In the past, PSAs were commonly thought to consist of a low‐density, turbulent suspension layer above, and sometimes in front of, a dense flow (Norem, ; Zwinger et al, ). However, observations from the 1980s or earlier from Canada (Schaerer & Salway, ), Russia (Bozhinskiy & Losev, ; Grigoryan et al, ; Sukhanov, ), and Japan (Nishimura et al, ; Shimizu et al, ) have shown the existence of a third region, sometimes called the light flow layer or the saltation layer. In recent years there has been increasing evidence of this third region, which has characteristics of both a dense region and a suspension region.…”

Section: Introductionmentioning

confidence: 99%

“…Signal fluctuations are clearly visible in many earlier data sets. Measurements of impact pressure and air pressure performed in the 1980s in Japan indicated the presence of oscillatory behavior in the dilute avalanche regions (Shimizu et al, ). The presence of snow balls of different sizes at different heights in the avalanche frontal region was studied by Schaer and Issler ().…”

Section: Introductionmentioning

confidence: 99%

The Intermittency Regions of Powder Snow Avalanches

Sovilla¹,

McElwaine

Köhler³

2018

JGR Earth Surface

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Powder snow avalanches are typically composed of several regions characterized by different flow regimes. These include a turbulent suspension cloud of fine particles, a dense basal flow, and an intermittency frontal region, which is characterized by large fluctuations in impact pressure, air pressure, velocity, and density, but whose origin remains unknown. In order to describe the physical processes governing the intermittency region, we present data from four large powder snow avalanches measured at the Vallée de la Sionne test site in Switzerland, which show that the intermittency is caused by mesoscale coherent structures. These structures have a length of 3–14 m and a height of 10 m or more. The structures can have velocities as much as 60% larger than the avalanche front speed and are characterized by an air/particle mixture whose average density can be as high as 20 kg/m3. This average density increases the drag on large granules by a factor of up to 20 compared to pure air, so that each structure can maintain denser snow clusters and single snow granules in suspension for several seconds. The intermittency region has importance for the dynamics of an avalanche, as it provides an efficient mechanism for moving snow from the dense layer to the powder cloud, but also for risk assessment, as it can cause large forces at large heights above the basal dense layer.

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A Study on High-Speed Avalanches in the Kurobe Canyon, Japan

Cited by 16 publications

References 0 publications

Inferences on Mixed Snow Avalanches from Field Observations

Inferences on Mixed Snow Avalanches from Field Observations

Velocity distribution in snow avalanches

The Intermittency Regions of Powder Snow Avalanches

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