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Author Topic: Avalanches, their causes, destructive power and so on.  (Read 11430 times)

paul.fr

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Dear people of the Geology section.

What are the main causes of Avalanches? How much force does an Avalanche pack? can i start one simply by shouting "helllooooo" whilst skiing? which one has killed the most people? where are they most frequent?

Thank you for your time, i know it's precious...
« Last Edit: 31/01/2008 02:20:28 by paul.fr »


 

Offline JimBob

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« Reply #1 on: 01/02/2008 23:10:13 »
Gee Paul, I thought it was self evident - avalanches are caused by snow. Do you need a more specific answer? Ask our ski instructor-geo. type person. I could tell you but I am too da** lazy. (or tired- can't tell which Driving yesterday and this morning was like driving down the Fort Collin to Pueblo Colorado in a Chanook wind. In my hi profile pick-up winds of 40-50 mph and gusting to 65. Not a refreshing drive.


 

Offline Bass

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« Reply #2 on: 03/02/2008 00:22:08 »
Dear people of the Geology section.

What are the main causes of Avalanches?

Too much snow pack on an unstable slope.  Virtually all avalanches happen on slopes between 30o and 45o  Any steeper and the snow doesn't stick, shallower slopes are stable.  The snowpack can become unstable for several reasons:

Too much snow- large storms or a buildup over time creates too much weight for the slope to hold.  This can be deep, dry snow, or thinner layers of "wet" heavier snow.

Layers can develope in the snowpack, which creates instabilities.  Dry sunny weather can crate a hard "crusty" layer on which subsequent snows will slide easily.  Wind and rain can also create layers.
The government avalanche folks around here are contstantly venturing into the hills to dig great, huge pits in the snow, which they then jump in to stare at blank walls of white for hours.  What they are trying to do is identify layers to help in avalanche prediction.

Wet snow on top of dry, light snow creates an ideal shear surface for snowslides.

Wind can increase the snow pack on the lee sides of mountains, and can pack the snow.

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How much force does an Avalanche pack?
Don't know the answer expressed in terms of physics- but I've seen avalanches knock down buildings and hurl vehicles hundreds of feet.  Also seen steel/concrete bridges destroyed and large forests leveled.
 
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can i start one simply by shouting "helllooooo" whilst skiing?

Possible, but not likely.  The avalanche would have to be on the verge of collapsing for the tiny force of your voice to set it off.  Most man-made avalanches are caused by skiers or snowmobilers cutting tracks across unstable slopes.  A 30 foot high (8 meters for you tea-sippers- SHEESH) is sufficient to bury a skier or snowmobiler.

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which one has killed the most people?

Don't have a clue.

 
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where are they most frequent?

In the mountains (DUH).  More common on the lee side of moutains or on the northeast sides- because of more snow due to wind and less sun.  Avalanches can occur any time of year, but happen most often in the spring due to heaviest snow loads and layering.

 

paul.fr

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Avalanches, their causes, destructive power and so on.
« Reply #3 on: 05/02/2008 07:17:17 »
Thanks, Bass
for a while there i thought i was going to have to rely on a decent answer from Jim!

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where are they most frequent?

In the mountains (DUH).  More common on the lee side of moutains or on the northeast sides- because of more snow due to wind and less sun.  Avalanches can occur any time of year, but happen most often in the spring due to heaviest snow loads and layering.



I mean where in the world, what mountain range...
 

Offline JimBob

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« Reply #4 on: 05/02/2008 18:14:37 »
I don't know if there has ever been a survey to determine this. It would be interesting.
 

Offline DoctorBeaver

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« Reply #5 on: 06/02/2008 12:03:14 »
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A 30 foot high (8 meters for you tea-sippers- SHEESH)...

I should like to point out that tea is most-commonly drunk in England and the Commonwealth countries where we still use feet & inches (a notable exception being China). It is the European coffee quaffers who prat about with metres due to their inability to calculate other than in tens.
 

Offline JimBob

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« Reply #6 on: 06/02/2008 15:41:32 »
Good for Old England - Up the EU!
 

Offline Bass

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« Reply #7 on: 18/02/2008 01:17:15 »
I mean where in the world, what mountain range...

Cobination of high snow loads, winds and open slopes would suggest mountain ranges like the Olympic Range in Washington, coastal range in B.C., or Alaska mostly due to their proximity to oceans and more than abundant rainfall/snow.  Southern Chile, southern New Zealand would also fit this profile.
 

Offline Exodus

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« Reply #8 on: 02/03/2008 15:12:13 »
Thanks, Bass
for a while there i thought i was going to have to rely on a decent answer from Jim!

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where are they most frequent?

In the mountains (DUH).  More common on the lee side of moutains or on the northeast sides- because of more snow due to wind and less sun.  Avalanches can occur any time of year, but happen most often in the spring due to heaviest snow loads and layering.



I mean where in the world, what mountain range...

Avalanches happen anywhere in the world... and the decisive factor is not their geographical location but its more down to the meteorological conditions... some areas may get a huge dumping of snow after a period of warm weather which has resulted in crust forming, this provides a perfect slip plain... all you need then is for wiond cornices to form higher up the slope and for a little to break off or a skiier/snowboarder to help it on its way.

The important thing is to not ride/ski alone, wear a tranciever if riding off piste/backcountry and carry a probe pole set and a shovel to and if you are caught in an avalanche, whilst you are moving try and swim your way towards the surface and as you feel the snow coming to a stop, you need to get your arms/hands in front of your face in order to create a breathing space... you then may have a chance to enlarge that upon standstill. It is important to move quickly if a friend is caught in an avalanche as people die pretty quickly! Fact is, if you stick to the trails and monitor the avalanche risks when you head out then the chances of getting caught in one are minimal... most resorts have people who go out early in the mornings and mortar dubious slopes to carry out controlled avalanches.
 

Offline Make it Lady

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« Reply #9 on: 06/03/2008 20:15:45 »
The biggest are always on cartoons, like the Simpsons and are caused by a really quiet noise after brass bands have been playing and klaxons have been sounding.
 

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« Reply #9 on: 06/03/2008 20:15:45 »

 

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