Wednesday, December 31, 2008

Winter Corner - December 31st 2008

This the last day of the year, and I was itching to go touring today. More importantly, I was interested in checking the snow coverage, ski conditions, and take a look at the snowpack structure.

The snotel data for Mores Creek summit suggest that the average SWE and precipitation might be reached during the next 24-48 hours as a storm arrives during the night. Although the ski lines above the 7,000 feet are fine, the ski out can made more fun (read less BRUSHY!) if average snow depth is finally reached. Last time, as I was coming out of Freeman, a snow bridge collapsed under me. I do not know what was funnier; the visual of last third of my ski/skins encrusted in ice and snow or my "cat like" skin-up from the creek banks! More snow will make the snow bridges above Mores Creek more reliable.
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I decided to tour Winter Corner since I was limited in time. But I also wanted to get snow pit data from a NNW exposure at 7,000 feet. Below a picture from the top of Winter Corner looking to the north. This ski line drops 1,000 feet, where the top is an open slope and the lower half wide spaced old growth forest.
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The ski conditions were interesting. Skiing in open slopes and meadows was fast (it almost felt slippery) in top of two crusts, where the bottom wind crust was supportable on my Big Atua skis. If you ventured too close to the trees - snow melt from Monday warm temps formed GESTAPO snow, with an amazing level of instructional content! The top melt freeze crust was delicate, and my boards easily broke through. Above this crust there was an ample supply of graupel. The graupel is spread uniformly across the whole hill. I observed the same graupel yesterday (Tuesday) while skiing at the local resort (Bogus Basin). Check the picture of the graupel included below:
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The next picture is an experiment with mix results, where I used my camera in top of my magnifier. Kind of Cool! Notice the size of the graupel. The squares are 1 x 1 mm. We will have to pay attention to this potential weak layer with the new snow arriving tonite.
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The snow pit is chart is included below:
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This snow pit is almost identical to the snow pit data shared in this blog for Freeman peak last December 28th. The new 20 cm of snow was today's trail breaking and riding surface. Both snow pits were to the ground, thus the snow depth went from 1.2 to 1.4 meters.

Two compression tests failed failed today (CTM11-Q2, CTM12-Q2) at the basal facet layer 10 cm above the ground. Extended Column Tests (ECT) for fracture propagation did not failed, most likely due to the weak layer exceeding the 1 meter depth. I did not conducted the Propagation Saw Test (PST) for fracture propagation, but based on the PST performed at Freeman Peak few days ago, I expected same results - a very energetic fracture propagation. Below a picture of the second column about to be tested.
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During the two CT tests the full columns were displaced approximately 3-4 cm. See the picture below for the displaced column. The tests were conducted on a 28 degrees slope. It is possible that a similar test on a steeper slope would have fully displaced the column, deserving a Q1 rating. However I rated the energy (quality of shear) as Q2.
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Another compression test was conducted but with a column isolated only to a meter in depth. The result was CTH24-Q3 on a storm interface at 90 cm formed during the December 26th storm.

The pause in storms have allowed the snowpack to adjust to the sudden snow loading and warm temperatures have allowed for the the sintering of the snowpack. It is reasonable to expect that it will be more difficult to trigger the weak facet layer buried at 1.3 meters considering its depth, and the bridging effect of the denser snow above. Not many places in Mores Creek are steep enough and at the same time lack the ground cover to be able to trigger deep slab avalanches, but be very picky. I suggest a HIGH dosis of prudence and caution as it is NOW easier travel farther. I expect some of the mini-cirques at the 8,000 feet elevation to be spooky - to say the least.

I will be looking forward to see many of you next year.

Happy NEW year! And may the new year bring many face shots days, and many years of good health to all of you.

Chago

Friday, December 26, 2008

Freeman Peak 12.26.2008

This is the first blog post after Christmas Day. And what a Christmas present we received - lots of NEW snow. Today skiing was nice, but the snow was slightly creamier than last Monday. This is the result of NE winds densifying the snow and new snow in the 10%+ moisture content. During my ski out I found the best and softer snow under the protection of old growth forest trees.
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Some of you are aware, the Avalanche conditions in the Sun Valley area are rated HIGH. My last three visits to the West Central Idaho backcountry show a different picture.The lower elevation of the West Central Mountains compared to the Sun Valley area terrain (Galena Summit, Boulders, Smokey, and Sawtooth Mountains) limited the snow cover early in the season. And at elevations above 7,00o the weak layer is mostly interlocked with the ground cover.
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Today as I skinned up to Freeman via the East ridge, below 7000 feet , it was impossible not to notice the many local collapses and cracks. Below a picture of one of the many cracks from Today.
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Above 7000 feet I did not observed any more local collapses and crack propagation. It is likely that the reason behind the collapse below 7000 feet is the more than 2 feet of snow in top of brush and ground cover. Snow is just sitting in the "air" until collapsed by trail braking.
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Below a picture of today's snowpit at 7200 feet. The pit aspect was NNE, and it was located on Freeman main East ridge, well below the ridge to avoid wind loading effects. The pit location was selected away from trees. Notice that the pit location was not steep, only 25 degrees.
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I was expecting a more complex snowpit. That was not case as you can see in the "Full study" snowpit data included below.
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I would like to remind the reader that the above pictures and chart are magnified by "clicking" on them!
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The compression tests were fair (CT scores of 20 and 22). "Sudden Collapse" failures occurred at the facet layer above an ice crust with shear quality of Q2. This weak layer is buried below 100 cm. The facet layer was relatively thick, about 10 cm. I was surprised that unlike other winter packs, there was no defined "cup" shaped depth hoar. Furthermore, the 2 mm facets on this layer right above the ground is part of a 7 cm thick decomposing ice layer.
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The temperature gradients (showed in the pit chart above) are not sufficient to enhance the formation of depth hoar, or promote the growth of the existing facets.
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Two fracture propagation test were conducted; Extended Compression and Propagation Saw Tests. The ECT was negative - no fracture propagation was observed. The PST failed after undercutting a length of 20 cm the weak layer (below 100 cm). The PST fracture propagation was energetic and the full 1 meter column was displaced by 5 cm after the collapse. It is likely that the "false positive" of the ECT was caused by small brush at the base of the column. In addition ECT cannot effectively transmit stresses below the 1 meter.
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Finally a review of the snowpack structure suggest the following structural weaknesses:
  • Weak layer is a "Persistent Grain Type".
  • Difference of hardness greater than one step from layer above.
  • Difference of hardness greater than one step from layer below.
  • Difference in grain size greater than 1 mm.
  • Weak layer thickness less than 10 cm.
  • Weak layer buried below 1 meter.

It should be noted that the last three structural weaknesses are right on the "borderline". Considering that the PST column displaced downhill on failure, I am not willing to ignore the 10 cm weak layer thickness criteria. And that the standard two CT tests collapsed, again I am not ready to discount the 1 meter depth criteria.

Based on the above the above tests and pit evaluation, the stability quadrants can be summarized:

Mores Creek area has abundant ground cover to lock the snowpack in place for instabilities near the ground, which is the case at this time. There are some areas where that is not true, thus caution should be exercised on steep slopes in the 7500-8000 feet elevation range. During the summer I have observed such areas. Maybe next summer I should catalog those areas for future reference.
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As noted earlier, above 7000 feet in elevation I did not observe any signs of instability. But the 6000-6500 feet elevation at NE exposures, some fractures can be found. The layer released was a soft slab between 20-30 cm, very likely a storm interface. This layer was identified in the snow pit, but during stability tests it was unremarkable.
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The next picture from Freeman Peak ridge (6300 feet) shows another soft slab release (1/3 from the top).

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One last comment; I continue to be concern about how many continue to use the bottom of the creeks to skin-up to Freeman and Pilot Peaks during periods of potential instability. During my 14 years of touring this area, I have seen avalanches release and come down into the creeks from the south aspects above the creeks. And these creek bottoms are DEADLY terrain traps!

Avalanches capable of burying people seem to be rare at Mores Creek Summit area, but they happen! Keep in mind that these south aspects have thinner snowpack, sparser ground cover, experience radiation recrystallization (near surface faceting) as well as Melt-freeze top layers are formed. All of this factors make the south aspects risky during periods of significant snowfall.

Below a topographic map of Pilot Peak , Freeman Peak, and Winter Corner areas. The red lines denote safe ridge access I use during instability and/or periods of snowfall. The ski runs in yellow are steep enough to slide during periods of instability. Keep in mind that these are NOT the only areas of avalanche danger!

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Enjoy the rest of the Holidays!

Monday, December 22, 2008

Pilot Peak - The Glades - 12.22.2008

Skiing at Mores Creek Mountain was fun today; cool weather, fantastic snow and great friends!
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As expected and typical of unconsolidated snow, trail breaking required considerable work. Depending on elevation between 40-50 cm of new snow was sitting on top of a poorly bonded and facetty snow, that kept collapsing under the skis.
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Below 6600 feet the snowpack showed lots of cracking and collapsing. But at higher elevations the snow was surprisingly non-cohesive, even when the water content was in the ~ 8%. The snow was not sufficiently "Champagne" light to guarantee face shots on every turn, but on the steeper runs, if you allowed the skis to run you could get "near" face shots!
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During our drive, as we approach Mores Creek Summit, several south facing road cuts showed signs of instability with recent fracture crowns from the the storm snow. However, no natural releases were observed anywhere in the Pilot Peak South, East, and North exposures at all elevations we skied. As noted earlier cracking and localized whumpfing was experienced elevations below 6600 feet, but no fracturing or local collapses were observed between 6600 and 7400 feet of elevation.
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Stability assessment on the slopes we skied is summarized in the chart included below.
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This is also a good opportunity to encourage the use of Rose diagrams. Included below today's observations captured in a Rose Diagram.
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On this link you can get a pdf version of the Rose diagram for your personal use:
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The conventions used to record snow observations can be found at American Avalanche Association website:
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The snowpack across Idaho mountains have a very WEAK structure. Today we did not find evidence of instability on the slopes we skied, but we were conservative. We did not skied anything steeper than 32 degrees, and for the most part we skied two north-east facing glades with sparse trees.
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As the snowpack continues to be loaded the triggering likelihood in the Idaho West-Central mountains area will augment, as well as the shear energy, in particular for steeper slopes. Furthermore, time will allow for the formation of cohesive slabs due to sintering metamorphosis. Please do not let your guard down!
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Feliz Navidad!

Sunday, December 14, 2008

2008-2009 Backcountry Ski Season

Today was my first ski day of this season. A late start considering that last year I was already skiing late in October.

Fritz, my son, and I toured Big Creek Summit today Sunday.



We found almost a meter of snow at the 7400 NNE aspect. The top 400 feet of skiing consisted of epic face shots. But below the 7000 feet the low density snow did not have a base. We managed to avoid serious damage to the boards, but it was definitely sketchy with the many rocks, deadwood, and stumps barely covered by the recent snow.

The snow pit for Big Creek is included below. Click on the image for a better view of the pit profile.



Stability tests (ECT and CT) and snow pit analysis suggested stable conditions. The weak layer below 60 cm deserves to be monitor. This facet weak layer might become reactive as the snowpack continues to be loaded and the top 60 cm gain strength thus becoming cohesive.

The snotel for Big Creek (6589 feet) reported a snow depth of 21.9 inches. That was consistent with our observations at the same elevation.

Mores Creek summit snotel reported today a snowdepth as high as 37 inches, considerably higher than the low 20 inches reported for Big Creek and Banner summits. Did anybody skied Mores Creek or Banner summit areas this Sunday? Can we get a ski and snow conditions report for Pilot/Freeman Peak or Copper mountain?

Wednesday December 17th I will conducting an Avalanche Awareness Session at the Fish and Game (Walnut Street). The event starts at 7:00 PM. The avalanche awareness topics to be covered are summarized in the following document Avi Awareness v2.pdf and it can be found in th efollowing link

http://santiago.livedrive.com/files

During the season I will continue posting useful documents.