Whitehorn II – D GullyPosted: January 14, 2012
Blue skies greeted avalanche control teams as they made their way to Whitehorn II yesterday morning to make the first foray of the season into D Gully. With no snowfall in the few days leading up to yesterday, there was little control work required in terrain that had already opened, and crews had the chance to continue work in closed terrain, getting it ready for its eventual opening.
In Whitehorn II, control work always begins at the far skier’s right, at A Gully. This gully, along with B Gully, starts lower than the rest, and is accessed by skiing along the fence line on skier’s left of Whitehorn I toward Rodney’s Ridge, then hanging a left where the fence turns to head down the fall line. Barely recognizable as a gully, A Gully is treated as a part of Rodney’s Ridge, and has been open for most of this season. Control teams will always leave a buffer next to open terrain – in this case, B Gully. In other words, for A Gully to open, B Gully needs to be controlled, too.
As one gully opens, teams move to the next, and so it goes until all of Whitehorn II opens. Yesterday marked the first control efforts in D Gully, and the start of a long process of control for a piece of terrain that is steep, complex, and, in addition to the main pitch of the gully, contains a few smaller cells that have characteristics all their own. This is true of all Whitehorn II gullies, and many rounds of explosives, bootpacking, and ski cutting are required to get the area ready to open.
D Gully has the largest start zone of all Whitehorn II gullies, and a number of explosive shots were used in this area. A start zone is where the bulk of wind-loaded snow usually ends up, and is therefore where most avalanches start. Two types of explosives were used – the usual dynamite-style charges, as well as bags of ANFO (ammonium nitrate & fuel oil). The smaller charges are thrown onto the slope and ideally will penetrate the surface layer so that the explosion has a better chance of reaching deeper into the snowpack, which is where the troublesome layers usually exist. On big slopes where the desire is for an explosive to cover a much greater area, ANFO is the ticket, as each charge can be built bigger or smaller depending on the wishes of the avalanche forecaster. The one used yesterday, for example, was about 7kg and packed a much larger punch than the usual hand charge would have, both outward and downward. If a slope doesn’t avalanche after an ANFO shot or two, control teams have that much more confidence in the stability of the slope and their ability to move safely on it, especially in the earlier stages of control work.
Prevailing winds generally blow across the slope from the skier’s left, which means that half of the gully will have more snow and therefore a greater potential for avalanches. With this in mind, five of us made our way down the right side, using ski cuts as we moved and stopping often to throw explosives on the left side. Happily, none of the shots produced significant results, which bodes well for the continued improvement of the slope. Much more work is needed, but good progress has been made, and every lap control teams make gets us closer to opening and having it available for all to enjoy.