Home > Trip Reports > February 26, 2009, Cascade East Slopes

February 26, 2009, Cascade East Slopes

2/26/09
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Posted by John Morrow on 2/26/09 9:28am
Probably wouldn't even be worth a TR today except that I had something interesting happen when I dug a pit.  Started the day with a skin track right out of the parking lot which was nice.  When it veered to other pastures, I continued up a rib that is very enjoyable skinning.  A couple of steep rolls on this rib provide a bit of a test slope opportunity with little consequence if something should move.  Nothing did.  At 5700 feet one has to continue on an east facing, sometimes windloaded, slope about 35 degrees steep.  Here I dug a pit, not expecting much, and mostly curious.  This is what I thought I found:  (Sorry, I work in rough inches and am not really scientific about it)

East aspect, 5800 feet, 35 degree slope
8" new, uncohesive fist hard on top
8" to ten inches of pencil/knife hard mega-crust"
Deep large grained facets below the crust.

The crust had a rough surface as I evidenced during the skin up.  So I really did not expect much movement upon it.  Planning a compression test, after sawing the sides I began my back cut.  I wasn't even through the back cut when it "popped" out atop the crust.  Not only that, but my supposedly cohesion less new snow came off in a uniform slab.  I looked at the bed surface for the answer to the fast and clean shear and there was about a 1/2 inch of finer grained facets on top.  I almost made the mistake of not studying the block that slid out.  I am glad I did because it solved it:  A second crust, one inch thick, separated from the mega crust by the 1/2 inch facetted layer.  In my haste looking at layers in front of the pit I wrongly assumed the crust to be one, based on the January rain.  The new snow on top was, in fact, uncohesive but "rode" that one inch crust off the facetted layer.

The real profile was more like this:
8" new fist
1" pencil crust
1/2 inch, 4 finger fine grained facets
6 to 8" pencil/knife mega crust
Lower facets

Fortunately, none of my switchbacks showed any movement or cracking on this slope and I never penetrated the top crust throughout the climb.  The thinner crust never collapsed under my weight.  Though it is not so good an indicator, the slope had been skied by more than a number of skiers as well.  Probably the only time I will ever ski a slope with a result of a zero in the compression test!

My first run was this east facing slope from 6000 feet to 5000 feet.  Mostly staying on top of the crust and floating in the new snow until toward the bottom 1/3.  This was a fun run.
My second run was same altitude on a north aspect where I found deeper snow and at times on steep slopes, up to 38 degrees, my thinner skis got caught in the soft crust.  I had a report from a friend that on fatter skis this wasn't problem.
Below 5000 to 4000 feet I was penetrating the crust regularly but in lower angle slopes. 
I guess a better teleier on fat skis would have had no problem today, and certainly an ATer on fat skis.  But I have had consistenly great snow for the past four weeks nearer to the crest and didn't really expect to be thrown a bit in a crust layer.   Still, a fun and interesting day none the less.  Thought I'd share my test results.
author=John_Morrow link=topic=12468.msg52077#msg52077 date=1235698111]
Probably wouldn't even be worth a TR today except that I had something interesting happen when I dug a pit.  Started the day with a skin track right out of the parking lot which was nice.  When it veered to other pastures, I continued up a rib that is very enjoyable skinning.  A couple of steep rolls on this rib provide a bit of a test slope opportunity with little consequence if something should move.  Nothing did.  At 5700 feet one has to continue on an east facing, sometimes windloaded, slope about 35 degrees steep.  Here I dug a pit, not expecting much, and mostly curious.  This is what I thought I found:  (Sorry, I work in rough inches and am not really scientific about it)

East aspect, 5800 feet, 35 degree slope
8" new, uncohesive fist hard on top
8" to ten inches of pencil/knife hard mega-crust"
Deep large grained facets below the crust.

The crust had a rough surface as I evidenced during the skin up.  So I really did not expect much movement upon it.  Planning a compression test, after sawing the sides I began my back cut.  I wasn't even through the back cut when it "popped" out atop the crust.  Not only that, but my supposedly cohesion less new snow came off in a uniform slab.  I looked at the bed surface for the answer to the fast and clean shear and there was about a 1/2 inch of finer grained facets on top.  I almost made the mistake of not studying the block that slid out.  I am glad I did because it solved it:  A second crust, one inch thick, separated from the mega crust by the 1/2 inch facetted layer.  In my haste looking at layers in front of the pit I wrongly assumed the crust to be one, based on the January rain.  The new snow on top was, in fact, uncohesive but "rode" that one inch crust off the facetted layer.

The real profile was more like this:
8" new fist
1" pencil crust
1/2 inch, 4 finger fine grained facets
6 to 8" pencil/knife mega crust
Lower facets

Fortunately, none of my switchbacks showed any movement or cracking on this slope and I never penetrated the top crust throughout the climb.  The thinner crust never collapsed under my weight.  Though it is not so good an indicator, the slope had been skied by more than a number of skiers as well.  Probably the only time I will ever ski a slope with a result of a zero in the compression test!

My first run was this east facing slope from 6000 feet to 5000 feet.  Mostly staying on top of the crust and floating in the new snow until toward the bottom 1/3.  This was a fun run.
My second run was same altitude on a north aspect where I found deeper snow and at times on steep slopes, up to 38 degrees, my thinner skis got caught in the soft crust.  I had a report from a friend that on fatter skis this wasn't problem.
Below 5000 to 4000 feet I was penetrating the crust regularly but in lower angle slopes. 
I guess a better teleier on fat skis would have had no problem today, and certainly an ATer on fat skis.  But I have had consistenly great snow for the past four weeks nearer to the crest and didn't really expect to be thrown a bit in a crust layer.   Still, a fun and interesting day none the less.  Thought I'd share my test results.

John,
good sleuthing on the snowpack analysis out east.    what you discovered is a classic NW feature initially described by Mark Moore (NWAC) in his PHD dissertation many moons ago.
Woody & I saw the same build up back in  the last weeks of Dec in the same neck_of_the_woods.  The ultimate revelation will be what happens to promote or degenerate the existing mega crust and the basil layer as we move towards inevitable melting...

Stop by some time at the 2nd st house after 1700h

author=fogle link=topic=12468.msg52127#msg52127 date=1235798061]
John,
Woody & I saw the same build up back in  the last weeks of Dec in the same neck_of_the_woods.  The ultimate revelation will be what happens to promote or degenerate the existing mega crust and the basil layer as we move towards inevitable melting...


Thanks for the reminder, Steve.  Last year in May we sure did have some dramatic slides after intense warming like the before and after shots below!  Good to keep it in mind...

Sounds like that half inch layer may be the same layer of rounds that was moving easily around Alpental today.  Could be a nasty one this week if the snow keeps coming.

author=Marcus link=topic=12468.msg52152#msg52152 date=1235877944]
Sounds like that half inch layer may be the same layer of rounds that was moving easily around Alpental today.  Could be a nasty one this week if the snow keeps coming.


Funny Marcus, I dug a hasty pit around Kendal Stump yesterday at 3800 feet, and found when I gave it a hand tug it moved on a good shear, but with a pretty hard tug on that south aspect: on those same rounds.

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february-26-2009-cascade-east-slopes
John Morrow
2009-02-26 17:28:31