Avalanche on Flagpole

TL;DR: I easily had enough time to ski away from the slough. The low light made it difficult to gauge the size and speed of it.

On the night of 1/22/2019 we (two skiers) went on a "full moon" run on Flagpole. With an advisory level of 2 and having skied Echo that morning and found no instabilities, we were comfortable with the risk level.

We skinned up the trees to take advantage of established skin tracks, and traversed lookers left from the summit to descend the open terrain. No red flags were observed on the skin up or on the traverse, but the illumination level impeded visual observations.

In the photo I am lookers right and entered the run first. A minor slough was triggered (but not seen) a few turns in. When stopping below that, the slough went over my skis and caused a loss of balance, but I was not entrained. At this point I traversed lookers left to a "safe zone", a small cluster of trees. Skier 2 then made a few turns and set off a bigger slough ("start of slide") before cutting sharply to lookers right. Skier 2 encountered unexpected rock drops on that traverse but was unscathed. 

The slide continued straight down to me. I thought I would be able to maintain my balance by holding onto the small tree, but when the slough hit my skis it immediately pulled me off and I slid approx 30 feet downslope to "arrested". I remained upright and was able to stop by digging into the slope with my skis. Had I not made any attempt to stop, or been separated from my skis, I could have followed the slide to the bottom. 

This photo was taken the morning after. It wasn't until that time that we realized how wide (100+ feet) and far (400 feet) the slide had gone. It was a slow moving affair of unconsolidated snow with no risk of burial on the open terrain, but could easily have swept me over the rocks below where I was caught.

Lessons learned or reinforced:

• always terminate a pitch at a "safe zone" that will be protected from a slide
• never ski directly above your partner if there's any concern about snowpack stability
• if you do see a slough approaching your position, ski away from it
• ski down the same (or similar) slope as the skin up to better gauge the conditions
• be more conservative in risk analysis when skiing at night
• when skiing conditions are less stable than your analysis predicted, exit the terrain at the first opportunity