11/13/10, Bearpaw Mountain
11/13/10
3148
8
This trip report is not so much of a trip report as it is relaying of an experience I had with my friend Chuck on Saturday to help remind folks to pay attention to snow conditions even in early season. We observed some interesting stability issues during our day and triggered a wet slab that appeared to be sensitive to a rapid solar, or weather system, induced temperature change.
The Bearpaw Mountain area off Canyon Creek in the NF Nooksack drainage is a sledders playground once the snow pack is deep. But in early season, it is left to self powered folk. We headed up there early Saturday morning to take advantage of some fun skiing in the area.
Early in the morning we encountered an obviously shallow snow pack (15 to 24). A variety of tests found the recent snow (from Thursday and Friday) was well bonded to the older snow from late October. However, there were two storm layers (3 and 6 down) within the recent snow that sheared rather easily but was not really cohesive, at least not along our route early in the morning. We took note and decided to not ski anything steep or with consequences (exposure, terrain traps).
After our first run of the morning and on our skin back up, the sun started poking through the clouds and almost immediately the east facing black cliffs of Bearpaw Mountain started dropping its snow, creating some rather large pin-wheels where a few minutes ago it was cold snow. This was interesting, and something I would certain expect in spring months, but not that extreme in November. We stayed away from this terrain and skied a moderate angled, more west facing, slope with another group of skiers (the famous internet group thanks guys for breaking trail on the second run). On that run, the snow was much heavier and we mostly were concerned with obstacles wrecking our skis.
Our third run was a more north and east facing slope of pretty moderate angle (no greater than 30 degrees) and again with wetter but still fun snow. Chuck and I decided to ski that run again, but this time I skied more onto the steeper side of a shallow gully to avoid crossing earlier tracks and triggered a 6 wet slab at my feet. I suppose this is not particularly surprising given our knowledge of the storm layers and warming, but we were surprised at the propagation and ending size of the slide given the mellow terrain. It stepped into some wind deposited terrain so the crown was well over a foot in places and ran as a slab around 30 40 meters where it stopped not really in pile, but a slab. The terrain was such that burial was not really possible, and since it broke at my feet, I easily turned out of the slide when it broke. It wasnt a safety issue for this particular slide, but it did get me thinking more about our decisions throughout the morning with a view to apply any lessons learn for future trips.
Three lessons (2 that we didnt apply well this day) include:
1) Dont overlook solar temperature changes at any time of the year. They are not limited to spring time, as the sun increasing in strength later in the year. I know this but was none less surprised at the rapid change in snow. The temperature change on Saturday may have occurred with or without cloud cover. However, the cliffs were actively dropping snow as soon as the sun hit them, and the snow pack progressively changed to wetter and heavier throughout the day finally resulting in a new balance between stable or not stable. The Baker telemetry data shows a change in temperature from high twenties to mid-thirties during the time we were skiing. This was enough to change the snow pack from unconsolidated drier snow to wet and cohesive at least in places. We knew the snow pack was getting heavier. We under estimated its ability to create a slab and be unstable. If this had been April or May, I probably would have been thinking about these issues more.
2) Our earlier assessment of snow led us to ski options limited to moderate angle terrain with low risk of consequences. This was due to the layers we identified, but also largely due to our conservative approach to skiing in a shallow snow pack. We never really thought outside the conservative box because of this.
3) Continue to assess conditions throughout the day, even on runs you have already taken. We normally do a better job at this, but we were distracted with the shallow snow pack focused on obstacles that could damage the skis. The fact that 5 skiers had previously skied this same run also influenced our lack of paying attention. Where I triggered the slide was in overall mellow terrain, but it happened to be the steepest part of that terrain, and probably a bit more wind loaded than other areas. My trigger point also was classic near a shallow point in the snow where a talus block was only a few inches below the surface. We knew the snow was heavier and there were those storm layers, but we werent thinking it could slide in an area we just skied. We all know this is an error in thinking.
Have fun and travel safe.
The Bearpaw Mountain area off Canyon Creek in the NF Nooksack drainage is a sledders playground once the snow pack is deep. But in early season, it is left to self powered folk. We headed up there early Saturday morning to take advantage of some fun skiing in the area.
Early in the morning we encountered an obviously shallow snow pack (15 to 24). A variety of tests found the recent snow (from Thursday and Friday) was well bonded to the older snow from late October. However, there were two storm layers (3 and 6 down) within the recent snow that sheared rather easily but was not really cohesive, at least not along our route early in the morning. We took note and decided to not ski anything steep or with consequences (exposure, terrain traps).
After our first run of the morning and on our skin back up, the sun started poking through the clouds and almost immediately the east facing black cliffs of Bearpaw Mountain started dropping its snow, creating some rather large pin-wheels where a few minutes ago it was cold snow. This was interesting, and something I would certain expect in spring months, but not that extreme in November. We stayed away from this terrain and skied a moderate angled, more west facing, slope with another group of skiers (the famous internet group thanks guys for breaking trail on the second run). On that run, the snow was much heavier and we mostly were concerned with obstacles wrecking our skis.
Our third run was a more north and east facing slope of pretty moderate angle (no greater than 30 degrees) and again with wetter but still fun snow. Chuck and I decided to ski that run again, but this time I skied more onto the steeper side of a shallow gully to avoid crossing earlier tracks and triggered a 6 wet slab at my feet. I suppose this is not particularly surprising given our knowledge of the storm layers and warming, but we were surprised at the propagation and ending size of the slide given the mellow terrain. It stepped into some wind deposited terrain so the crown was well over a foot in places and ran as a slab around 30 40 meters where it stopped not really in pile, but a slab. The terrain was such that burial was not really possible, and since it broke at my feet, I easily turned out of the slide when it broke. It wasnt a safety issue for this particular slide, but it did get me thinking more about our decisions throughout the morning with a view to apply any lessons learn for future trips.
Three lessons (2 that we didnt apply well this day) include:
1) Dont overlook solar temperature changes at any time of the year. They are not limited to spring time, as the sun increasing in strength later in the year. I know this but was none less surprised at the rapid change in snow. The temperature change on Saturday may have occurred with or without cloud cover. However, the cliffs were actively dropping snow as soon as the sun hit them, and the snow pack progressively changed to wetter and heavier throughout the day finally resulting in a new balance between stable or not stable. The Baker telemetry data shows a change in temperature from high twenties to mid-thirties during the time we were skiing. This was enough to change the snow pack from unconsolidated drier snow to wet and cohesive at least in places. We knew the snow pack was getting heavier. We under estimated its ability to create a slab and be unstable. If this had been April or May, I probably would have been thinking about these issues more.
2) Our earlier assessment of snow led us to ski options limited to moderate angle terrain with low risk of consequences. This was due to the layers we identified, but also largely due to our conservative approach to skiing in a shallow snow pack. We never really thought outside the conservative box because of this.
3) Continue to assess conditions throughout the day, even on runs you have already taken. We normally do a better job at this, but we were distracted with the shallow snow pack focused on obstacles that could damage the skis. The fact that 5 skiers had previously skied this same run also influenced our lack of paying attention. Where I triggered the slide was in overall mellow terrain, but it happened to be the steepest part of that terrain, and probably a bit more wind loaded than other areas. My trigger point also was classic near a shallow point in the snow where a talus block was only a few inches below the surface. We knew the snow was heavier and there were those storm layers, but we werent thinking it could slide in an area we just skied. We all know this is an error in thinking.
Have fun and travel safe.
Thanks for this excellent writeup sharing your observations of variety in snow stability in a very small area depending on terrain, wind affect, and sun.
nice report, thanks for the heads up
Thanks ebeam. We had a similar experience that day as we walked out from our northwest facing ski near there at similar elevation - we left as powder was transitioning to styrofoam - but just before crossing a rock rib on a 35 + degree NW facing windpocket, I popped a slab 10 inches deep that didn't run anywhere, but instantly shot a crack out to my partner 10 yards in front of me on the other side of the gentle rib, popped on the windslab around shallow rocks. Not what we were expecting but not surprising in hindsight.
Hmm, that is interesting. I was up taking a few runs off table that morning. I did notice a couple of flat spots that had small wind slab like characteristics and there was obvious compacting as I skinned up. Other than that nothing moved while I skied or tried to kick things off. I left at 10am and there was a big difference in the snow lower down by the parking lot. It was getting heavy and sticky about that time. What elevation were you at and what time of day did the slide happen?
There were so many people up at baker it was like homecoming ball. Also curious if any of them saw things change up there later or found any of the farther chutes loaded.
There were so many people up at baker it was like homecoming ball. Also curious if any of them saw things change up there later or found any of the farther chutes loaded.
I was with Eric and what supprised me with the slide was we were continuously monitoring the snowpack and discussing slide potential but the snow wasn't "that slabby" and the different bed layers were not that clean. We thought that yes there could be a point release on the steeper parts but probably not a slab. As the day progressed the snow pack settled and changed its bonding.
When the slab cut loose the crown line didn't propagate perpendicular to the fall line but was about 45 degrees off the fall line. I don't think the snow was bonded strong enough to be able to crack across the slope but instead due to it settling and being a little moist (it wasn't what I would call wet) it held together enough to be able to crack. The snow had not cooled enough to bond into a stronger slab where it had enough tensile strength to "pull" the latterly across the crown line but instead the fracture move downhill as much as across the slope. Viewing the bonding of the slab it was almost like it behaved between a point release and a slab. But I must say it was an impressive crown line and as Eric mentioned it started at a weak (shallow point) right at the crown (convex) spot of the run. In viewing the crownline one could really read the cross loading - the crown varied from about 6" to 18" in a number of places.
I guess the point of this post is it is avi season!
When the slab cut loose the crown line didn't propagate perpendicular to the fall line but was about 45 degrees off the fall line. I don't think the snow was bonded strong enough to be able to crack across the slope but instead due to it settling and being a little moist (it wasn't what I would call wet) it held together enough to be able to crack. The snow had not cooled enough to bond into a stronger slab where it had enough tensile strength to "pull" the latterly across the crown line but instead the fracture move downhill as much as across the slope. Viewing the bonding of the slab it was almost like it behaved between a point release and a slab. But I must say it was an impressive crown line and as Eric mentioned it started at a weak (shallow point) right at the crown (convex) spot of the run. In viewing the crownline one could really read the cross loading - the crown varied from about 6" to 18" in a number of places.
I guess the point of this post is it is avi season!
Just curious if you took pics of the slide, surroundings, or skiing?
Where did you go up? How far were you able to drive?
Did you go up Whistler Creek or to the end of the outlet of Bearpaw Mtn. Lake?
Did you go up Whistler Creek or to the end of the outlet of Bearpaw Mtn. Lake?
author=RonL link=topic=17957.msg75993#msg75993 date=1289916356]
What elevation were you at and what time of day did the slide happen?
We were around 5600 ft elevation and approx. noon for time of the slide.
TobyT - no pictures, but if you look on a map we were skiing off the small summit (6K elevation) south of Bearpaw Mountain and following the drainage that first runs NE and then turns N (heading toward and ending at Church Lake). This is the summit immediately south of the saddle that sledder's use to access the Whistler Creek basin
Stefan - Yes, we used the Whistler Creek Rd system; drove to about 3700ft. Others went further later in the day.
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