Avalanche

avalanchesavalanchingavalanche researchavalanche rescueavalanche risksavalanche transceiverClass 4 avalancheslab avalanchesnow scientistsnow slide
An avalanche (also called a snowslide) is a cohesive slab of snow lying upon a weaker layer of snow in the snowpack that fractures and slides down a steep slope when triggered.wikipedia
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Natural hazard

natural hazardsnaturalhazard
In mountainous terrain, avalanches are among the most serious objective natural hazards to life and property, with their destructive capability resulting from their potential to carry enormous masses of snow at high speeds.
Geophysical hazards encompass geological and meteorological phenomena such as earthquakes, volcanic eruptions, wildfires, cyclonic storms, floods, droughts, avalanches and landslides.

Powder snow avalanche

powder avalanche
The largest avalanches form turbulent suspension currents known as powder snow avalanches or mixed avalanches.
A powder snow avalanche is a type of avalanche where the snow grains are largely or wholly suspended by fluid turbulence.

Snowpack

snow packsnow quality
Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack (slab avalanche) when the forces of the snow exceed its strength but sometimes only with gradual widening (loose snow avalanche). After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow.
Assessing the formation and stability of snowpacks is important in the study and prediction of avalanches.

Mudflow

mudslidemudslidesmud flow
However, they are distinct from slushflows which have higher water content and more laminar flow, mudslides which have greater fluidity, rock slides which are often ice free, and serac collapses during an icefall.
Some broad mudflows are rather viscous and therefore slow; others begin very quickly and continue like an avalanche.

Rockslide

avalanchesrockslides
Slides of rocks or debris, behaving in a similar way to snow, are also referred to as avalanches (see rockslide ).
Fast-flowing rock slides or debris slides behave similarly to snow avalanches, and are often referred to as rock avalanches or debris avalanches.

Snow

snowfallsnow covernival
An avalanche (also called a snowslide) is a cohesive slab of snow lying upon a weaker layer of snow in the snowpack that fractures and slides down a steep slope when triggered.
A sub-specialty is avalanches, which are of concern to engineers and outdoors sports people, alike.

Angle of repose

the maximum possible sand slopean engineering termcritical angle of repose
The angle of the slope that can hold snow, called the angle of repose, depends on a variety of factors such as crystal form and moisture content.
It is also commonly used by mountaineers as a factor in analysing avalanche danger in mountainous areas.

Landslide

landslideslandslipdebris avalanche
However, they are distinct from slushflows which have higher water content and more laminar flow, mudslides which have greater fluidity, rock slides which are often ice free, and serac collapses during an icefall.
An avalanche, similar in mechanism to a landslide, involves a large amount of ice, snow and rock falling quickly down the side of a mountain.

Slush flow

slushflows
However, they are distinct from slushflows which have higher water content and more laminar flow, mudslides which have greater fluidity, rock slides which are often ice free, and serac collapses during an icefall.
While frequently compared to an avalanche, they have some key differences.

Gravity current

density currentdensity currentsGravity current box models
If the avalanche moves fast enough, some of the snow may mix with the air forming a powder snow avalanche, which is a type of gravity current.
Examples include avalanches, haboobs, seafloor turbidity currents, lahars, pyroclastic flows, and lava flows.

1999 Galtür avalanche

Galtür avalancheavalanche of GaltürGaltür avalanche disaster
Scientific studies using radar, following the 1999 Galtür avalanche disaster, confirmed the hypothesis that a saltation layer forms between the surface and the airborne components of an avalanche, which can also separate from the bulk of the avalanche.
This avalanche was considered the worst Alpine avalanche in 40 years.

Mass wasting

mass movementmass-wastingrotational slip
As an avalanche moves down a slope it follows a certain pathway that is dependent on the slope's degree of steepness and the volume of snow/ice involved in the mass movement.
These include avalanches, mudflows, debris flows, earth flow, lahars and sturzstroms.

Snow cornice

cornicecornicescornice of snow
Slopes in the lee of a ridge or of another wind obstacle accumulate more snow and are more likely to include pockets of deep snow, wind slabs, and cornices, all of which, when disturbed, may result in avalanche formation.
In avalanche safety, cornices are a high avalanche danger as they often break and trigger larger avalanches that permeate several snow layers.

Avalanche dam

Engineered drainages, such as the avalanche dam on Mount Stephen in Kicking Horse Pass, have been constructed to protect people and property by redirecting the flow of avalanches.
Avalanche dams (anti-avalanche dams, avalanche protection dams) are a type of avalanche control structures used for protection of inhabited areas, roads, power lines, etc., from avalanches.

Winter of Terror

1950–1951 winter-of-terror avalanchesin the winter of 1951
This series of avalanches killed around 265 people and was termed the Winter of Terror.
when an unprecedented number of avalanches took place in the Alps,

Wellington, Washington

WellingtonWellington DisasterAn avalanche in 1910
Two avalanches occurred in March 1910 in the Cascade and Selkirk Mountain ranges; On March 1 the Wellington avalanche killed 96 in Washington State, United States.
The Wellington avalanche was the worst avalanche in the history of the United States, marked by the total death count, which numbered to 96.

Depth hoar

When a temperature gradient greater than 10 °C change per vertical meter of snow is sustained for more than a day, angular crystals called depth hoar or facets begin forming in the snowpack because of rapid moisture transport along the temperature gradient.
Depth hoar crystals bond poorly to each other, increasing the risk for avalanches.

2012 Gayari Sector avalanche

20122012 Siachen Glacier avalancheavalanche hit a Pakistani military headquarters
Siachen Glacier
On 7 April 2012, an avalanche hit a Pakistani military base in Gayari Sector, near the Siachen Glacier region, trapping 140 soldiers and civilian contractors under deep snow.

Saltation (geology)

saltationsaltatingsaltation layer
Scientific studies using radar, following the 1999 Galtür avalanche disaster, confirmed the hypothesis that a saltation layer forms between the surface and the airborne components of an avalanche, which can also separate from the bulk of the avalanche.
Saltation layers can also form in avalanches.

Ski resort

ski areaski resortsaprès-ski
Preventative measures are employed in areas where avalanches pose a significant threat to people, such as ski resorts, mountain towns, roads, and railways.
With enough excess water, the likelihood of landslides and avalanches may be drastically higher.

Mark the Mountain Guide

Mark the Mountain Guide: Avalanche!: a children's book about an avalanche that includes definitions & explanations of the phenomenon
In the first book, Mark the Mountain Guide, this includes child-friendly explanations of what causes an avalanche, how mountains are formed and why stars are so bright at altitude.

Alps

Alpinethe AlpsAlpine region
During World War I, an estimated 40,000 to 80,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian-Italian front, many of which were caused by artillery fire.
In the 17th century about 2500 people were killed by an avalanche in a village on the French-Italian border; in the 19th century 120 homes in a village near Zermatt were destroyed by an avalanche.

Montroc

9 February 1999 Montroc avalanche
A large avalanche in Montroc, France, in 1999, 300,000 cubic metres of snow slid on a 30° slope, achieving a speed in the region of 100 km/h.
Montroc was partially destroyed on the 9th of February 1999 by a slab avalanche on the Mont Blanc massif, killing 12 people.

Entrainment (physical geography)

entrainedentrainmententrain
Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack (slab avalanche) when the forces of the snow exceed its strength but sometimes only with gradual widening (loose snow avalanche). After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow.

Serac

seracssérac
However, they are distinct from slushflows which have higher water content and more laminar flow, mudslides which have greater fluidity, rock slides which are often ice free, and serac collapses during an icefall.