Building the Colorado snowpack

[pechelman]

What effects do vegitation and the local terain play in the pack formation?
What going on around these features: Is there a TG and related transformation? - or something else?
At what point does an "anchor" like feature do more harm than good? - or vise a versa?
Is there any relation that might make one feature "better" than another? - ie. A grassy slope vs. one covered with knee high willows.
Whats up with whumphing? Early season (in the base pack) I'd bet it's usually a TG layer letting go but what about later in the mid & upper pack.

Im by no means an expert, having only read books, but a lot of this seems to extensively crossover into my other areas of expertise, mechanical, materials, and composites engineering. Soo heres how Id try to answer the questions given my miniscule avalanche knowledge in conjuction with my engineering background.

Anchors only do good when they are disperesed in such a way that their distribution per area of snow pack is great enough to support the added stresses from the snow pack and disturbances, ie travel. The larger the anchor generally the better. A large conifer with 10foot diameter branches will do a lot more good than a very large rock for multiple reasons. The first Id think is a temperature issue, in that the TG would be larger with the rock due to its large mass and great proximity and contact with the warmer ground. Second, The shape of a conifer, generally cone shape, is the PERFECT shape to most evenly distribute any stress into the snow pack. Lastly, the confier is a flexible non-rigid anchor. What would you rather fall onto, a pane of glass or a trampoline? Additionally, your photos give clear illustration that when the distribution pattern of anchors is near the top and sides of a steeper (35-40deg) wind loaded slope, the fracture will generally occur at these anchors. Generally speaking since its the top of a ridge or something above tree line, these anchors are generally rocks. This ties directly into my engineering background that a fracture will propogate from stress concentration to stress concentration. I think its important to consider anchors also as stress concentrations in the snowpack because for them to work as anchors, they need to be supporting extra stress. Anchors imo just makes them sound too safe. I know thats the proper terminology, Im just offering my opinion here.

Regarding the grassy slope vs willow; Are you implying that the grass would act as an insulator in hope to reduce the TG from the ground? Im not so sure that would be the case, and it would definitely seem to hurt the ground\snow interface strength for potential full depth slides early\late season. All things being equal, it seems like the knee high shrubs ala scrub oak and bushes would be preferred.

Settlement cones seems like they might be working its way into this conversation as well with vegetation and local terrain features. I guess the important thing there is to not take them at face value like an anchor vs stress concentration and maybe see them as a settlement cone vs inconsistent snowpack. The new snow is nice and strong, but who knows the history below it without digging now or previous digging?

I thought whumphing was the weak layer collapsing under stress?
Wouldnt that follow that whumphing anytime in any depth of the pack would be the same thing? Im curious to know if thats the case.

Anyway hopefully this isnt too far from being correct and helping in the discussion. If its not, Ill delete it because I dont want someone to get wrong information that sounds logical. (i hope it sounds logical)

edit to make it more clear and stuff

[FrankZappa]

Regarding the grassy slope vs willow; Are you implying that the grass would act as an insulator in hope to reduce the TG from the ground? Im not so sure that would be the case, and it would definitely seem to hurt the ground\snow interface strength for potential full depth slides early\late season. All things being equal, it seems like the knee high shrubs ala scrub oak and bushes would be preferred.

What I meant is, (assuming that TG is relevent to vegitation like it is to ground), would the depth be more consistent and posibly less prone to triggering if the vegitation gets flattened before the build. Kind of lessening the total depth of the sugar snow. I tried to sketch it here.

[FrankZappa]

Also, now that I think about it, vegitation I don't think holds/generates much heat (or cold) by itself like th ground would, but I would think that it absorbs sunlight (heat) even when buried (like the big dust layer last season did) and thereby has an effect on the surounding snows transformation.

[FrankZappa]

Update: For a whole bunch of avy terms and some great explainations check out the Avalanche Encyclopedia at Avalanche.org
This Encyclopedia is brought to you in cooperation with:
National Avalanche Center and
The Friends of the Utah Avalanche Forecast Center.

------------------------------------------------------------
Here's some misc junk I found out there somewhere...

temperature gradient 
Meteorology rate of change of temperature with distance.
The rate of change of temperature with displacement in a given direction from a given reference point.
n : change in temperature as a function of distance (especially altitude)


from wiki
Hoar frost (sometimes hoarfrost) refers to the white ice crystals, deposited on the ground or exposed objects, that form when the air is moist and surface is cold. Hoar frost is often seen on cold, clear autumn nights.

Hoar frost is similar in appearance to rime ice, but the two are distinct. In formation of hoar frost, the water vapour condenses through deposition directly to solid ice whereas rime ice is formed following initial condensation into liquid droplets. Thus, hoar frost is formed when the dew point is warmer than surface but colder than the air temperature, and colder than freezing point. The formation of frost is an example of meteorological deposition.



hoar frost (–noun frost (def. 2). )
frost 
1. a degree or state of coldness sufficient to cause the freezing of water.
2. Also called hoarfrost. a covering of minute ice needles, formed from the atmosphere at night upon the ground and exposed objects when they have cooled by radiation below the dew point, and when the dew point is below the freezing point.
3. the act or process of freezing.
...


Dew
1. moisture condensed from the atmosphere, esp. at night, and deposited in the form of small drops upon any cool surface.
2. something like or compared to such drops of moisture, as in purity, delicacy, or refreshing quality.
3. moisture in small drops on a surface, as tears or perspiration.
...


dew point 

the temperature to which air must be cooled, at a given pressure and water-vapor content, for it to reach saturation; the temperature at which dew begins to form.

Also called dew-point temperature.
Compare absolute humidity, mixing ratio, relative humidity, specific humidity.


relative humidity 
the amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature; the ratio of the actual water vapor pressure to the saturation vapor pressure. Abbreviation: RH, rh

[AltaPowderDaze]

I woke up before the crack of shit thinkin' about three more TG related things.

• Terrain - in a very Local sense
• Vegitation
• Whumphing

Some of the biggest whumphing I've run across seems to have happened (or have been triggered) where a combination of these things occur. And, as I recall, in quite a few of the avy reports I've read about and looked at, many times the crown fractures from one of these randomly placed features to another to another and so on.

Note that what I'm refering to as "local terrain" are faetures that extend above the general plane of the ground such as rocks, boulders or maybe deadfall...
And in terms of vegitation in this case generally I'm addressing the "lower level" stuff like grasses and bushes - lets say thigh high and lower.

So here's some of the assiciated questions:
What effects do vegitation and the local terain play in the pack formation?
What going on around these features: Is there a TG and related transformation? - or something else?
At what point does an "anchor" like feature do more harm than good? - or vise a versa?
Is there any relation that might make one feature "better" than another? - ie. A grassy slope vs. one covered with knee high willows.
Whats up with whumphing? Early season (in the base pack) I'd bet it's usually a TG layer letting go but what about later in the mid & upper pack.

if you are hearing whoomphing, you a experiencing a collapse in the snowpack. another words, a weak layer just failed. the slab may not fail due to slope steepness, anchors or the flanks, crown and stauchwall may provide sufficient cohesion.

the anchors often grow facets around themselves. firstly there is the temp gradient issue but there is also typically low density there, which allows for quicker development of advanced facets. that anchor/feature can only effect the snowpack up to its height. what it can do is cause inconsistencies in the snowpack, which are likley points for a crown to run since they weaken it. poke some holes in a line on sheet of paper and try to tear it near the first one. the path of least resistance often wins.


hacksaw should be you best bet for the flattened vs. standing vegitation. my take on it is just personal theories and probably more relevant to intercontinental snowpacks.

[homerjay]

Whumphing is an avalanche without a slope to slide on, essentially.

Pechelman, I don't necessarily agree with you. Rotten snow exists around trees all the time...size/shape doesn't matter. Sparsely spaced trees = trigger points and tight trees = anchors. Having wallowed through waist deep sugar in willows, I think they serve to transfer heat higher up into the snowpack, thus increasing the TG whereas grass is smaller, closer to the ground, and more uniform.

Oh, and it's raining like hell here, snow above 10k. No way anything above timberline and north facing is going to melt out this year before 'winter.'

[pechelman]

Pechelman, I don't necessarily agree with you. Rotten snow exists around trees all the time...size/shape doesn't matter. Sparsely spaced trees = trigger points and tight trees = anchors. Having wallowed through waist deep sugar in willows, I think they serve to transfer heat higher up into the snowpack, thus increasing the TG whereas grass is smaller, closer to the ground, and more uniform.

yea i suppose i was being a little too ideal with the trees in that I essentially ignored temperature effects, especially if a well were to form around the base. i think you summed up what i was trying to say in a few words, "Sparsely spaced trees = trigger points and tight trees = anchors."

[smitchell333]

So here's some of the assiciated questions:
What effects do vegitation and the local terain play in the pack formation?
What going on around these features: Is there a TG and related transformation? - or something else?
At what point does an "anchor" like feature do more harm than good? - or vise a versa?
Is there any relation that might make one feature "better" than another? - ie. A grassy slope vs. one covered with knee high willows.
Whats up with whumphing? Early season (in the base pack) I'd bet it's usually a TG layer letting go but what about later in the mid & upper pack.

In my experience Vegetation tends to rot the pack. Absorbs heat and radiates into the pack - thus more TG and depth hoar development

Rocks are similar - esp if they stick out above the snow surface as then they absorb sunlight's warmth rapidly

I dont think "anchors" are really beneficial for the most part. As you can see in the Trap Park slide pictures small trees often act as release points - as APD mentions with his analogy of the hole in paper - they act as weak points from which propogation can occur. People mention dense trees as evidence that anchors hold the pack. I think this is a fallacy - in my experience the reasons that denser trees can limit avalanches have more to do with 1) wind sheltering that limits slab development, 2) trees break up any potential slab into smaller areas which can be less likely to slide in avys of consequential size.

The only exception - when anchors might be beneficial is where the snowpack comes down very wet or becomes very wet and refreezes (ala spring) but since that isnt likely here in CO - I'd say forget it and consider them a potential menace.

Grass vs. willows - grass is a better bed surface - a slab will be more likely to slide on grassy then in a thicket of willows - although willows will tend to rot things out more.

As far as the "flattening effect" - I'd say its only likely with grasses or very small bushes and therefore inconsequential.

Back to the Colorado Snowpack - I havent been up since last Monday, but from one of the TR's posted it looks like the TG and D Hoar development is underway:

[FrankZappa]

Just some more samples of vegitation/terrain variables.

Think about what all this stuff's like in winter. & whats going on down there.

From MBSC's TR: Mtn Biking in Crested Butte, June & July thread... Grasses in the foreground and hillsides, but check out the willows in that path there.
You won't know that stuff's there in winter.


Some places the ground vegitation gets pretty thick (at least by Colo. standards).


and lots of times it's thin, but there can be lots of rock (terrain features)

[FrankZappa]

I got a couple messages like this one on this thread

Also, I like your snowpack thread! It's an interesting read. Thanks for keeping it going. I've stayed off b/c I don't really feel like I have enough experience historically to contribute, but it sure is an interesting read

This thing's gettin' a lot more reads than I expected and I just want to encourage everyone to participate and ask questions. I doubt anyone's gonna get JONGed for something like that. Besides, if they do that'd be better than not knowing or thinkin' the wrong way about somethin'. Who knows, maybe it'll save someones neck. Anyways, keep the thoughts flowin' through here so we can all learn more.

It seems to be a good time of year to be thinkin' about these things.

I'm no expert on this stuff, but I've been runnin' around in the Colo. BC for over 25 years without a mishap, so I must be doin' somethin' right.



Now I know why everybody claims to be a dentist around here - It's like pullin' teeth sometimes. Thanks to all who've tossed in thier two cents so far.

[iskibc]

It's good to see a lengthy and highly educational thread in this forum. Some really good points brought up and discussed. Nice work everyone.

As for the vegetation topic, I've found that vegetation and ground surface types play a big role in early season/thin snowpack situations, but slowlly become obsolete once a deep base is achieved. In some locations a deep base never comes about no matter what time of year, so knowing what you are standing on top of is really important. However, the opposite also holds true. Some areas build up a deep and thick base quickly and the ground surface quickly becomes a lesser concern. In the case of a deeper base, I'm more concerned with the mid-layers or the most recent storm/series of storms. There's quite a bit of variance from one bc location to another, especially here in Colorado since the wind factor, localized weather factor, and temperature variance factor all come into play.

I've found that tall grassy/willow areas tend to be weaker in nature and much more rotten than shorter, smoother surfaces. The reasoning is quite obvious as willows/tall-thick grass are stronger and create air pockets, variance in snow depth from one bush to the other, and an overall unevenness to the snowpack. Also, willows and tall grass tend to create a higher temperature gradient than most other surfaces. Of course, most of this is due to snow depth. If you have 10' sitting on top of a slope that has a lot of willows and tall grass, then most likely that vegetation will be flattened and the vegetation factor won't be as important as the same slope with only 2' on top.

[smitchell333]

...In the case of a deeper base, I'm more concerned with the mid-layers or the most recent storm/series of storms. There's quite a bit of variance from one bc location to another, especially here in Colorado since the wind factor, localized weather factor, and temperature variance factor all come into play... If you have 10' sitting on top of a slope that has a lot of willows and tall grass, then most likely that vegetation will be flattened and the vegetation factor won't be as important as the same slope with only 2' on top.

Good thoughts - Add aspect and elevation to the variation that you can see in the pack. There have been times when higher elevation slopes have been pretty solid, but once you get below treeline the pack is totally rotten underneath and I'd be scared to death on a steep open slopes. Also another effect is that west facing slopes can get scoured and then later recieve thin coverage that goes TG/Depth Hoar rapidly.

I think one of the key lessons of this discussion that you always have to think, observe, and be ready to change your opinion of the snowpack and route selected based on what conditions are - esp here in Colorado where things can vary so severely.

[Ireallyliketoski2]

This is a great thread. I'm always amazed that an average 6 mile ~3,000 foot tour here in CO can yield a dozen different snowpacks, with maybe the best pack being at a moderate level of danger. This renders pit data completely useless sometimes as little as 50 feet away.

This uncertainity in the snowpack makes me believe that one of the biggest keys to staying alive in avalanche terrain here in CO is the ability to "read" terrain and evaluate route selection. I've found that when people come from a moutaineering background as well as a skiing, they are generally much better at this.

[FrankZappa]

OK. So how 'bout we get some new blood in here to see if we can sumarize what we've got so far? (preferably in 500 confusing words or less )

Then we'll build it up some more.

Volunteers...?

[Buster Highmen]

This uncertainity in the snowpack makes me believe that one of the biggest keys to staying alive in avalanche terrain here in CO is the ability to "read" terrain and evaluate route selection. I've found that when people come from a moutaineering background as well as a skiing, they are generally much better at this.

I'd agree, except:
0) That's true anywhere, not just CO.
1) It's more a function of being out in exposed areas a lot where you really need to pay attention. Then one begins to develop a sense of what's more likely to side than not and what exposure really is.

[FrankZappa]

Lets see whats up with some layering. I'll borrow a lil' example from CAIC's site again. Specifically the slab and weak layers.

This is in the form of what I consider the typical "early" season build that we can expect to see over the next few months.

Kelso Mountain
December 22, 2005
2 hikers caught, 1 partly buried, 1 buried and killed

Avalanche
Though very broad, this combination soft slab and hard slab avalanche was classified as medium-sized relative to the avalanche path (HS/SS-AF-R3/D3-O). The avalanche fractured 750 feet across the east-facing slope, but only released about 2 feet deep. The weak layer was a 3-4-inch thick layer of small, loose, faceted grains. The avalanche ran at least 460 vertical feet with the north end spreading across the summer trail. Along the summer trail the slope was very shallow but steepened to 37 degrees. Because of the weather conditions, it is very reasonable that this avalanche was a natural release.

This photo shows the slab and weak layers just above the fracture line (that was buried by drifting snow). The top slab was one-finger hard. Below was a 4-finger weak layer of small faceted -- sugar snow -- grains. Below this layer was another firm layer -- 1-finger-- of wind-drifted snow. Below was another weak layer of faceted grains. The rest of the snow cover of strong, hard, consolidated snow to the ground.

The avalanche likely fractured on the upper-weak layer as this was consistently the weakest layer in stability tests -- compression tests ranging from 7 to 12 with quality 1 and 2 shears -- in the starting zone). The slope angle is 37 degrees in steepness.

Photograph, Dale Atkins 12/24/2005

Sooo... Here's some questions to ponder.
What's kinds of things are causing the formations in there? You know, where did those weak faceted layers come from?
Are they all over the place or just in localized areas?
What's goin' on with the temperatures in the different depths of the pack? - What does this do?
What else is effecting this build?
What are these lurking layers gonna be like mid to late winter?

Maybe having these weak early layers can be a good thing. If there is a big dump and some wind, hopefully these will let go & wipe out all this junk. Then we'd get a clean slate to rebuild, right? Or... what else can we expect over the next few months?

[Ireallyliketoski2]

Maybe having these weak early layers can be a good thing. If there is a big dump and some wind, hopefully these will let go & wipe out all this junk. Then we'd get a clean slate to rebuild, right? Or... what else can we expect over the next few months?

That certainly can happen and is often nice when it does. However, the next few months are going to see consistent deep snow falls throughout all Colorado mountain areas, the storms will come in warm and end cold for maximum adhesion and blower. By February we will have a 12' deep isothermic snowpack with no depth hoar or weak layers.

[FrankZappa]

That certainly can happen and is often nice when it does. However, the next few months are going to see consistent deep snow falls throughout all Colorado mountain areas, the storms will come in warm and end cold for maximum adhesion and blower. By February we will have a 12' deep isothermic snowpack with no depth hoar or weak layers.

I like the way you're thinkin' here.


but...


is that it? Thats all the feedback I can get out of you guys?

[smitchell333]

Maybe having these weak early layers can be a good thing. If there is a big dump and some wind, hopefully these will let go & wipe out all this junk. Then we'd get a clean slate to rebuild, right? Or... what else can we expect over the next few months?

Would be nice - but I dont think it wipes it out if it slides - slide paths have been known to run multiple times on the same layer of facets/DH at the bottom. The only things that really alleviates it once it develops are either very warm temperatures or lots of snow.

[AltaPowderDaze]

The only things that really alleviates it once it develops are either very warm temperatures or lots of snow.

don't forget about the rain.

[AltaPowderDaze]

Would be nice - but I dont think it wipes it out if it slides - slide paths have been known to run multiple times on the same layer of facets/DH at the bottom.

repeaters are often self sustaining. if it slides down to less than 4' of snowpack left, you will see rapid development of facets w/o lots of snow in the next 48hrs. more next time it gets loaded it can release on the newly developed facets from the temperature gradient.

[lemon boy]

don't forget about the rain.

Rain? In the winter? UNPOSSIBLE. (it is a lot rarer here than in UT)

FZ- to turn things yet again: what would be the best situ given that the Sept. snowfall is likely gonna stick around and were gonna get a bit more this w/e....?

[smitchell333]

what would be the best situ given that the Sept. snowfall is likely gonna stick around and were gonna get a bit more this w/e....?

A LOT more snow as in 3-4' base ASAP

[FrankZappa]

Rain? In the winter? UNPOSSIBLE. (it is a lot rarer here than in UT)

FZ- to turn things yet again: what would be the best situ given that the Sept. snowfall is likely gonna stick around and were gonna get a bit more this w/e....?

As I remember it has rained in CO right around New Years day the last two winters in a row. - at least I know it did 2 years ago & I seem to remember it at least trying to last winter.

...que words on global warming now.


As for the best situ from here on, I would still fall back to the series of smaller storms that have the chance to bond well to each other. I would think something a few feet thick that is cohesive throughout and has had the time to settle while it's been building (hence the smaller storms) would provide the least amount of stored energy.

Plus we still have some fairly mild temps goin' on when it's clear which is more similar to when it storms - reducing huge thermal fluctuations.

And I don't think the wind is up to it's full on forces like we get mid winter - at least not as consistent - so that might help by reducing the loads here and next to nothing there. You know, make the build over the junk more consistent throughout.

So, lets say that that happened 'til we got up to around 50" on the ground by... mid Dec. Then we get some good ol' big(er) dumps. Some places will cycle & some won't, but if bonding happens and we get up a nice deep pack (like 7-8 feet) in late Jan-ish I think we'd have a pretty strong thick build in general that someone on the surface would have a hard time triggering the deep crap at the bottom. At that time I think we need to be more concerned with the upper layers and whats going on up there. But... triggering the upper stuff can definately lead to stepping down into that junk below.

Course by then we have stuff like creep, loading... changing the energy components within the pack. But I think the TG at the base then becomes less of a concern. And there's faceting going on up in these mid/upper layers too. I don't know much about these buried mid pack facet layers but I assume they occur much the same way the depth hoar at the ground level happens = TG. - at least that makes the most sense to me, with the temp variations that hapen throughout the entire pack. Different layers seem to "store" different temps (up and down temps - not one continous gradual change from surface temp to ground temp). or maybe due to different densities in different layers the rate of change in the temps happens at different speeds throughout the pack. (?)

Sooo, in my own conclusion: I dunno for sure, Whatdya think?
Que "Call bullshit" here. I won't ever learn something new if somebody doesn't speak up.

[AltaPowderDaze]

Course by then we have stuff like creep, loading... changing the energy components within the pack. But I think the TG at the base then becomes less of a concern. And there's faceting going on up in these mid/upper layers too. I don't know much about these buried mid pack facet layers but I assume they occur much the same way the depth hoar at the ground level happens = TG. - at least that makes the most sense to me, with the temp variations that hapen throughout the entire pack. Different layers seem to "store" different temps (up and down temps - not one continous gradual change from surface temp to ground temp). or maybe due to different densities in different layers the rate of change in the temps happens at different speeds throughout the pack. (?)

the mid pack layers were once the near surface facets or possibly surface hoar. they grow the same as the depth hoar you see at the bottom but in the opposite direction. the crystal builds layer upon layer in what resembles a trapazoid. the widest end is the most recent and the direction of the vapor transfere.

frank, if you'll look back through the avalanche review of about 2 yrs ago, there's a really good article on vapor trasnsfere and faceting around crust layers/impedence layers (above and below).