shallow snow avalanche?

[Blakej]

When snow is only 2-3 ft deep is there likely to be a significant slide? I'm assuming so. Also considering a block test wouldn't be possible in snow of that depth what is the best test for this fall snow we are experiencing. I noticed some small slides while out this weekend but even with the different consistancys of snow it seemed pretty stable but I hate to assume its safe by just trauncing around on the unexposed parts. Just doesn't seem too scientific. Comments?

[cj001f]

Why wouldn't a block test be possible? Cut block, jump. Analyze results.

 

With the melt/freeze cycle we're going to see shortly things are perfect for slides.

[snoboy]

Hmmm, a lot of questions all wrapped up in your post there Blake...

 

At this time of year, I really like to know what is under the snow, 2-3 feet of snow on top of a grassy slope is a lot more of a hazard than 2-3 on top of a field of large talus. The underlying "texture" can make a big difference to how well things are anchored.

 

I don't see why a rutschblock would not be possible in that snowpack? Perhaps you could explain why you think it would not work?

 

I would be wary anytime I see natural slides occuring, this is obviously an indicator of some sort of instability. I really wouldn't be describing something as "pretty stable" if I saw slides occuring! In fact I would call it quite unstable.

 

Sticking to unexposed areas is a great way to be safe, if by that you mean areas that are not possible to slide, and are not exposed to possible slides from above.

 

There are really a couple of elements at play in the winter risk management game - probability of an event (avalanche) and consequences (if one happens.) The probability is the tricky one to predict, but there are sometimes obvious signs (whoomphing, cracks propogating, natural slides occurring) and other times you need to dig in and have a look at the snow.

 

The second part of the question is easier to answer, Look around you, get your head out of the snow pit, and ask your self, "What if?"

 

What if the slope in question slides? Is there enough snow to bury me? Is there a terrain trap (gully, bench, streambed) that could make for a deeper burial? Maybe there is a cliff just below you, and a slide that is not big enough to bury you could still knock you off and kill you.

 

Unfortunately there is little science in avalanche prediction, at least at the level of techniques available to the backcountry traveller. That said there area lot of things that you can do to make your trips safer, and more enjoyable. Taking a basic avalanche awareness course is a good first step, and getting out in the b/c with experienced people is vital IMO.

[Blakej]

Ok so to clarify better here is the situation that triggered the question.

While doing a climb this weekend we acended a fairly steep (maybe 50 degrees at times) reentrant that was about 200ft wide. At times we would post hole through soft stuff to our knees and hit solid ground but as we got further up the slope the snow was crusty on top at times but we would break through to softer stuff and then more regularly straight up hard to kick steps into. There were some obvious small slide areas in the center which we avoided by staying close to the rock and shallower snow.

The reason I though a block test wouldn't work is that I would hit dirt before I was able to get a decent size block to jump on. Secondly the inconsistantacy of the snow didn't seem like it would give an accurate depiction of the overall snowpack. I guess I could just dig to dirt and then jump and try this on each different consistancy of snow I found but I didn't think that would be very dependable at the time. Perhaps I was wrong. Though I feel pretty confident in the saftey of the approach we took and my partner who is far more experienced in snow travel was not concerned it did raise the question.

[catbirdseat]

I am not familiar with the term "reentrant".

[Macson]

Look up reentrant gully on google. Also look up "reentrant angle". In my mind, I picture a steep gully leading to a ridge with inward facing walls of less than 90 degrees.

[cracked]

Two or three feet is enough to create a 1 foot thick slab that can take you for a ride, maybe even bury you if the terrain is right.

[savaiusini]

Two or three feet is enough to create a 1 foot thick slab that can take you for a ride, maybe even bury you if the terrain is right.

Cracked, how would you know? Do you have some sort of first hand experience?

[Blakej]

sorry reentrant is more of an orienteering term. maybe wide couloir would have been a better way to say it.

[cj001f]

Two or three feet is enough to create a 1 foot thick slab that can take you for a ride, maybe even bury you if the terrain is right.

Depending on the sliding surface (grass or granite being prime) 2 or 3 feet is enough for a ..... 2 or 3 foot slab.

[bDubyaH]

we had a woman die up here in a shallow snowpack (<2-3') she was cutting across a slope on snowshoes, when it released and buried her in a terrain trap. this was at a time when much of the area was fairly bare. if there is enough snow to cover the ground, then there is enough to slide. treat early season snowpack the same as you would mid-winter. analyse it (dig a pit), look for any instabilities, play it safe until your brain gives you the green light to drop in on the big lines. best to lilve another day.

cheers

[Gaper_Jeffy]

treat early season snowpack the same as you would mid-winter. analyse it (dig a pit), look for any instabilities, play it safe until your brain gives you the green light to drop in on the big lines. best to lilve another day.

 

Always good advice.

 

To reiterate what snowboy and cj100f said, when the snowpack is shallow it's important to consider what is on the ground. Vegetation and rocks may play a significant role in anchoring the slope. A permanent snowfield on a volcano may not have any anchors and should warrant more caution.

[alienPDX]

There is a great recent example of a shallow slide (with photos) here

http://mtnphil.com/ORock3/ORock3.html

[iain]

wow, this thread got edited heavily! I still think my (deleted) advice stands. Apparently someone does not think so.

[fern]

Iain said:

anyone making decisions in avalanche terrain based on advice from cc.com is out of their friggen skull.

[fern]

catbirdseat said:

You are badly misleading a lot of newbies who may not understand your joke. A suitable terrain trap could take that 2"-3" of snow, funnel it and concentrate it as it slides, to produce enough snow to bury you under feet of snow. People need to learn to recognize terrain traps. There is a good example of one up near Paradise that buried a snowboarder when snow funnelled into a gully.

[fern]

blakej asked:

 

to add on to the questions. I know that soft hard soft can lead to disaster but what about a hard inch thick crust on top of a foot or two of softer snow. I understand the top crust could break and slide but is it a significantly less danger?

[iain]

Perhaps I could have worded that better, I apologise...

 

I would take a skeptical approach to comments on cc.com, particularly those involving your life safety. You can't be sure of who you are talking with, what their background is, and even what the intention of their post was. Likewise, the poster can't possibly predict the variables that will be presented to you on a given day when you have to make those life-dependent decisions, even if the poster is an acknowledged expert in the field.

 

It's been said a million times, but nothing can replace hands-on training under the supervision of experienced teachers. I would consider any advice here supplementary at best, highly suspect at worst. But you probably already know that.

 

As Twain wrote: Be careful about reading health books. You may die of a misprint.

[iain]

blakej asked:

to add on to the questions. I know that soft hard soft can lead to disaster but what about a hard inch thick crust on top of a foot or two of softer snow. I understand the top crust could break and slide but is it a significantly less danger?

 

And now for a suspect response

 

The quality of shear in your hasty pit analysis will help guide you to your decisions on whether a given interface will slide. It is only one data point among many, and pit work really should only confirm what you already suspect about a snowpack. However, quality of shear on compression or shovel tests will go a ways towards determining the stability of an interface you have questions about.

[Gaper_Jeffy]

anyone making decisions in avalanche terrain based on advice from cc.com is out of their friggen skull.

Well said. I completely concur with this advice.

[MisterMo]

blakej asked:

 

And now for a suspect response

 

 

To which I will add an even more suspect response: the very closest I have come to being offed in an avalanche happened on a Thanksgiving weekend, in MRNP, at about 5000'. The snowpack wasn't very deep but apparently it was deep enough as I sent off a helluva slab. Sooo: If it's deep enough to ski on it's probably deep enuff to slide.

[mattp]

Several years ago, I was skiing up on Granite Mountain in the Spring and got caught quite unaware of the hazard on a south facing slope where rocks and grass were showing through the surface in such profusion that I had no idea there was anything that could slab. Also, the snow that I was skiing on was pretty much bulletproof, and this gave me an even greater sense of security.

 

However, I heard a loud crack as a hard slab released in a shallow gully that I hadn't even identified as a gully, and the slide ran several hundred feet to pile up blocks the size of file cabinets at the bottom. Had I been just a little more aggressively skiing the slope when it went off (I had met a patch of rocks I didn't like as I was skiing downhill and was slowly traversing onto the slab as it released from the tips of my skis forward - rather than skiing downhill at full speed and ending up on top of it), I would have been severely pummeled or killed.

 

By the way, I'll add that there is plenty of good advice to be had here on cc.com. Obviously, nobody says you should take anonymous posters word for it when it comes to making your own life-or-death decisions, but it is equally dis-serving to suggest that one should not ask about such things on this site or that there is no value in asking about or discussing matters of safety.

[iain]

I'll add that there is plenty of good advice to be had here on cc.com ... it is equally dis-serving to suggest that one should not ask about such things on this site or that there is no value in asking about or discussing matters of safety.

 

Of course, I was not suggesting there is no value in these discussions. However I could see, for example, someone posting the blanket statement "there is no avalanche danger on mt st helens" w/o really thinking about it. I didn't mean to appear overly negative - you can learn a lot on cc.com. I know I have.

[fern]

just so its clear iain, your post was removed accidentally because it was sandwiched in some nonsense that was drifting an otherwise good thread off-track. Thank you for your contributions

[Blakej]

Lets see so what I got is baby steps and don't be an idiot and drown in a shallow bathtub... Seriously thanks for all the ideas to add to my though process.