Large-scale Avalanches Research Articles

Effects of Snow Avalanche Disturbance on Regeneration of Subalpine Abies mariesii Forest, Northern Japan

We examined the effects of snow avalanche on stand structure and the subsequent regeneration of subalpine Abies mariesii Mast forest in northern Japan, and discussed whether gap formation after avalanche disturbance leads to immediate seedling establishment or not. Tree size and age, tree-ring chronology, and seedling density were compared between, on, and around a relatively large avalanche path, which was created in the mid-1980s within Hachimantai National Park. On the avalanche path, only smaller and younger trees (height <5 m, 50–100 yr old) escaped the mechanical damage of avalanche by leaning into the remaining snowpack, and old canopy trees were mostly killed by stem breakage. Tree size structure of the avalanche path, including both living and dead individuals, was relatively similar to that of nearby undisturbed forest, indicating that a mature stand (>ca. 200 yr old) had been previously developed on the avalanche slope without large-scale disturbances in the past. Most of the surviving, younger trees showed abrupt growth release during the few years (1987–1989) after the avalanche event. However, densities of both post-avalanche (<15 yr old) and pre-avalanche (≥15 yr old) seedlings were much lower on the avalanche path than in the nearby forest, especially at microsites covered with dense dwarf bamboo (Sasa kurilensis) shrub. The pre-avalanche seedlings on the avalanche path sharply increased annual height growth rates after the mid-1980s avalanche, but such positive growth response did not continue longer than 6 to 7 yr. These findings suggested that gap formation following the infrequent, large-scale avalanche disturbance did not necessarily lead to immediate seedling recruitment and/or further growth release of pre-avalanche seedlings. The constraint of seedling establishment was primarily explained by the lack of potential seed supply, and shading effect of the dwarf bamboo bush. Consequently, post-avalanche regeneration of the subalpine fir forest was likely to depend on the smaller individuals (2–5 m in height) that were able to avoid both the mechanical damage of avalanche and mortality from shading by the dwarf bamboo.

Large-Scale Avalanche Braking Mound and Catching Dam Experiments with Snow: A Study of the Airborne Jet

We report a series of ongoing large-scale experiments to studythe interaction of a snow avalanche with a dam and a row of mounds which are of a comparable height to the flow depth.The experimental results indicate that the behaviour of thesupercritical flow around the obstacles is governed by the large-scale properties of the flowing avalanche rather than micro-scaleproperties of the granular current.The experiments show that, similarly to smaller-scale experimentswith glass particles, the avalanche detaches from the top of the dam or mound and forms a coherentairborne jet, which can be modelled as a two dimensional ballistic projectile with negligible air resistance.We study the two parameters that define the trajectory of thejet, namely the speed at which the jet is launched from the top of the obstacle and the deflection of the jet by the obstacle, and compare the resultswith a theory for the deflection of a jet of an ideal fluid.

Avalanches in the draining of nanoporous Nuclepore mediated by the superfluid helium film

When capillary-condensed superfluid ${}^{4}\mathrm{He}$ drains from pore spaces in the nanoporous material Nuclepore, the fluid drains in a series of large-scale avalanches in which substantial numbers of pores (up to $\ensuremath{\sim}2.5%$ of the sample) drain as a single cooperative event. In this work we document the behavior of such avalanches in a number of different multiple-detector configurations in an effort to investigate the origin of the interactions among the pores that lead to the avalanche behavior. We conclude that the presence of a superfluid ${}^{4}\mathrm{He}$ film on the surface of the Nuclepore plays a significant role in causing the avalanche behavior. We also investigate aspects of the spatial distribution of pores that are involved in an avalanche event, and conclude that avalanche events involve pores that are distributed over the entire sample; avalanches do not typically involve a high-density cluster of pores in a local region of the substrate.

Avalanche behavior in the draining of superfluid helium from the porous material Nuclepore

Examination of the primary draining curve in studies of the capillary condensation of ${}^{4}\mathrm{He}$ in the porous material Nuclepore reveals that lowering the chemical potential when the helium is in the superfluid state causes the Nuclepore pore spaces to drain in a series of large-scale avalanches in which substantial numbers of pores (up to $\ensuremath{\sim}2.5%$ of the sample) drain as a single cooperative event, i.e., as an avalanche. In this work we document the behavior of such avalanches in this porous material for two characteristic diameter pore sizes 200 nm and 30 nm. We examine the relevance of various theoretical models which one might apply to the system and conclude that none is completely satisfactory.

Introduction to the Special Issue of the Symposium on deep-seated landslides and large-scale rock avalanches

Introduction to the Special Issue of the Symposium on deep-seated landslides and large-scale rock avalanches

１９９２年５月４日白馬大雪渓の大雪崩について

１９９２年５月４日白馬大雪渓の大雪崩について

Experimental Studies on a Powder-Snow Avalanche

To make clear the structure and behaviour of a large-scale avalanche, the impact force-data obtained in the avalanche project of 1972–78 were analysed in detail. The wave forms of impact forces are classified into two types. Type 1 is composed of many separate spikes each of which represents the collision of a snow block. Type 2 has wider peaks, caused by collisons of snow blocks mixed with fluidized snow. Most of the type 1 peaks were in the width range corresponding to 0.005–0.01 s duration, and most type 2 peaks fell into the 0.02–0.1 s range. The internal velocities of an avalanche were estimated by calculating cross-correlation spectra for a time series of impact-force records. It was discovered that these internal velocities varied from 10 to 50 m/s over time. The mean distance between snow blocks was found to be in the range 1.6–5.4 m in a type 1 avalanche, and between 0.7 and 3 m in type 2 avalanches. Sizes of snow blocks or snow clouds of type 1 and type 2 were in ranges 0.26–0.52 and 0.37–1.9 m, respectively. This paper also reports on the project created to initiate artificial powder-snow avalanches in the Shiai-dani area and to make systematic observations of a variety of physical aspects. Results obtained in 1988 for both artificial and natural avalanches are given.

Experimental Studies on a Powder-Snow Avalanche

To make clear the structure and behaviour of a large-scale avalanche, the impact force-data obtained in the avalanche project of 1972–78 were analysed in detail. The wave forms of impact forces are classified into two types. Type 1 is composed of many separate spikes each of which represents the collision of a snow block. Type 2 has wider peaks, caused by collisons of snow blocks mixed with fluidized snow. Most of the type 1 peaks were in the width range corresponding to 0.005–0.01 s duration, and most type 2 peaks fell into the 0.02–0.1 s range.The internal velocities of an avalanche were estimated by calculating cross-correlation spectra for a time series of impact-force records. It was discovered that these internal velocities varied from 10 to 50 m/s over time. The mean distance between snow blocks was found to be in the range 1.6–5.4 m in a type 1 avalanche, and between 0.7 and 3 m in type 2 avalanches. Sizes of snow blocks or snow clouds of type 1 and type 2 were in ranges 0.26–0.52 and 0.37–1.9 m, respectively.This paper also reports on the project created to initiate artificial powder-snow avalanches in the Shiai-dani area and to make systematic observations of a variety of physical aspects. Results obtained in 1988 for both artificial and natural avalanches are given.