Does this make any sense to you?

[Roo]

Wikipedia's entry on the Galtur Avalanche of 1999.


"The Cause

The cause of the avalanches puzzled scientists for a long period of time. Although the area was prone to avalanches, never before had they occurred on such a scale as this, reaching the village. A complex sequence of events led to the event: 4000km away, on the 20th of January, an Atlantic storm was forming. Turbulent warm air from the tropics headed north, and, cooling, it swung back towards Europe. This started a series of storms.

Combined with cold arctic air coming from the north, there was a very dry, light snowfall exceeding 4m. A massive snowpack formed on the mountains above Galtür. Northwest winds piled the snow to increasing depths. A melt-crust developed in late January, formed when solar energy thaws the upper snow layers in the day, but it then refreezes at night. At Galtür, it bonded with ice and hence lasted longer than they were generally known to. The resulting powder avalanche contained a central layer scientists were not previously aware existed. Known as the saltation layer, it was primarily responsible for the destruction of buildings[3]."

[Arno]

That reads like a much longer bit of prose which has been precised by someone who doesn't really understand the original

[StevieG]

Reads like the voiceover for a TV doc. I remember watching one on the Montroc slide which possibly had a similar preamble - was Galtur the same season?

[CookieMonster]

No, this doesn't make sense unless you can fill in the missing pieces. Generalities notwithstanding, a dry flowing avalanche is:

Dense Core ( Granular Flow Mechanics )
Powder Cloud ( Fluidised Air/Snow Mixture )

Both components can cause damage, but the density of the powder cloud is usually very low, even if it moves very fast, relative to the density of the flowing core. Highly destructive avalanches need a combination of high density and high velocity to produce high impact forces.

I have heard the Galtur disaster referred to as a "powder avalanche" but many destructive avalanches have both a powder cloud and a dense core ( the powder cloud is produced because the snow is dry; the powder cloud obscures the dense, flowing core ). The term "powder avalanche" is frequently misused and often applied to any avalanche with a powder cloud, regardless of whether or not the avalanche is actually a true "powder avalanche".

The author of the Wikipedia text may be referring to some notion that the Galtur avalanche was composed entirely of snow suspended in the air.

Saltation refers to a type of particle motion, and while I have heard of this term used in reference to avalanche dynamics, the term usually refers to wind-transported snow. I.E. Most wind transport occurs through saltation in the lowest metre above the snow surface. Snow that is carried up into the wind is subject to evaporation and/or is deposited outside avalanche starting zones.

Saltation may occur on the top of the dense core of the avalanche. Saltation as a "layer" in the snowpack? No.

Link

[Hacksaw]

Saltation refers to a type of particle motion, and while I have heard of this term used in reference to avalanche dynamics, the term usually refers to wind-transported snow. I.E. Most wind transport occurs through saltation in the lowest metre above the snow surface. Snow that is carried up into the wind is subject to evaporation and/or is deposited outside avalanche starting zones.

Saltation may occur on the top of the dense core of the avalanche. Saltation as a "layer" in the snowpack? No.

Maybe the author is trying to explain how slab formation can happen...

[CookieMonster]

Maybe the author is trying to explain how slab formation can happen...

Agreed. Just idle speculation while I avoid doing real work!