Observation Date: 11/09/2013
Carlton Ridge and terrain nearby.
Skied a 250 ft NE 30 degree facing chute. Wind loaded with nice consolidated powder.
Dug Pit 40 ft down from entrance on approx 34 deg slope, skiers left of gut. 18 inches powder on top of 6 inches of consolidated (firm) snow.
CT22 on a traverse (diagonal and crumbly) plane @ 18 inches. “Lets go skiing!” (Right?)
Perfect Ski Weather. 30 degrees and grey bird to sunny.
Very little wind.
New Snow: No New Snow
Snow from Mid-week had settled into nice bouncy powder on less wind affected slopes. Signs of significant wind affect from previous 3 days. Wind had likely transported significant amounts of snow recently (wed, thurs, fri).
from above… “Whuumphh!”
Upon entrance to the chute, a crack propagated 40 ft across the top of entire chute. The top 18 inches shifted maybe a 1/4 of an inch and stopped.
Had this gone… our skier would have likely been seriously injured or worse.
Observed Danger Rating:
We had been on North, South, Southwest, and west slopes all less than 30deg with no signs of instability.
Pit results were good.
What did I do wrong?
1 Lulled into false positive by lack of complexity of snowpack.
2 Lack of concentration while executing test.
There probably was a failure @ < 10 that I missed in the snowpit test. Most likely on a buried surface hoar or facet. Though I have dug hundreds of pits, I was a bit too excited this day. I had expected a positive result due to lack of numerous layers. I didn’t closely observe the one interface that was present. The column probably shifted ever so slightly, but because the top 18 inches of powder compressed significantly on taps 1-10, I didn’t notice.
The Pit test did probably describe the stability fairly accurately. Though there was an interface failure, the slope didn’t slide. In the pit (steeper than gut) the column probably failed, but did’t move due to enough friction after failure.
This of course was mostly luck.
I got an early reminder this season (first day) that hundreds of pits an hundreds of successful days in avalanche terrain doesn’t guarantee a proper pit interpretation. Please be very careful out there. Never expect positive results. If you only dig one pit – pay 100% full attention. Better yet dig two with 100% full attention.
Observer: Steven Geiger