Red Flags In Reality is a Jones Avalanche Awareness Month series detailing live-from-the field stories about five of the most common signs of avalanche danger-the Red Flags. First up, learn about the dangers of wind loaded snow from an experience Seth Lightcap went through in Hakuba, Japan.
There was a slight breeze at the trailhead, but nothing striking. Same story climbing up through the trees – just a gust of wind here and there. But when we gained the ridgeline, some 2000 feet above the streets of Hakuba, Japan, it was a whole different story. The wind was nuking.
It hadn’t snowed in a few days but there was enough loose snow around to make strong gusts the icy equivalent of a shotgun blast to the face. Our drop-in point was only a couple hundred yards down the ridge so we pulled up the masks, flipped up the hoods and charged into the wind. All things considered, compared to the winds we face in the High Sierra, it wasn’t all that uncomfortable for me. I’d struggled through nastier wind storms for a lot longer before. Maybe that’s why I missed the sign, or rather, the slap-in-the-face.
Climbing up we had seen no evidence of natural avalanche activity. No whumpfing, no shooting cracks, no crown lines, no roller balls – just 3-6 inches of three day old fresh snow that was seemingly well-bonded to a buffed base layer. We had seen enough avy activity in our week in Hakuba to be on guard, but when I dropped off the ridge I was not in full-danger mode. My gut thought was that the conditions weren’t that dangerous because there was not very much fresh snow and we hadn’t seen many explicit avalanche “Red Flags” that day…except for the most obvious one of course – the icy shotgun sprays to the face.
The Five Red Flags of Avalanche Danger include: 1) Recent/current avalanche activity 2) “Whumpfing” sounds or shooting cracks 3) Recent/current heavy snowfall 4) Strong winds transporting snow 5) Rapid warming or rain on snow.
The combination of my comfort in high winds and casual assessment of the available snow for transport led me to make a grave mistake when I rolled off the ridge. No, I didn’t kick off a massive slide two turns into a wind-loaded panel, but I did plant myself in a very stupid spot and proceed to get swept by a six inch deep slab avalanche set off by another rider entering the slope.
I was carried a 1000 feet down a gully and beat within an inch of my life because I failed to recognize an obvious red flag. The ridge top winds were more than enough to load the gully with a shallow soft slab and to my surprise, a slab doesn’t have to be that deep to carry some serious energy. I am not alone in the mistake I made that day. Unrecognized wind slabs cause a majority of avalanche accidents and fatalities worldwide. The sensitivity of wind deposited snow catches a lot of backcountry shredders slipping.
I look out for all the Red Flags when I am touring, but strong winds have become more like a ‘hot pink with flashing strobe lights’ kind of avy danger flag for me. When there has been fresh snow and it’s windy or has been windy, I tip-toe into the mountains until I make observations that show limited danger.
A working knowledge of how wind transports snow will help you understand the potential for wind deposition relative to the wind speed. There are three ways wind can move snow – Creep, Saltation and Turbulent Suspension.
Creep is the rolling of snow crystals along the surface of the snow (within 1/2 inch). Creep occurs at low wind speeds (under 12 mph) and accounts for about 10% or less of snow transported by wind.
Saltation is the transport of snow within about three feet of the snow surface. Saltation occurs at moderate wind speed (12-30 mph) and by most studies, accounts for the majority of the snow transported by wind.
Turbulent Suspension is when snow particles get taken up into the wind column and carried a longer distance by high winds (over 30 mph). At mid-high wind speeds (30-60 mph) a lot of snow gets transported by suspension but at high wind speeds (greater than 60 mph) much of the snow is either transported beyond avalanche start zones or lost to sublimation (the snow changes into water vapor).
Wind speed determines the amount of wind loading. Winds between 20 and 60 mph are ideal for transporting snow. Winds less than 20 mph can only transport very low-density snow (< 5%) on the ground. Average speeds between 30 and 40 mph will deposit snow of almost any density onto avalanche start zones and have the greatest potential to build dangerous slabs.
The combination of new snow and wind-deposited snow increases the snow accumulation rate exponentially. The snow depth can easily double or even quadruple on leeward slopes. If snow falls at a rate of 1 inch per hour for 8 hours, there would be 8 inches on the ground but if winds average 30-40 mph throughout that period there could be snow depths of 16-32 inches on leeward slopes.
Check out the chart above to better understand the effects of wind speed on wind loading danger and keep these facts in mind the next time you head into the backcountry on a windy day or after a windy storm. I ignored that icy, slap-in-the-face, red flag of wind loading, and nearly paid the ultimate price. Don’t let it happen to you.