After climbing the first pitch on the lower headwall we found a small crevasse to belay from. Brian led the next pitch, placing a couple pickets while I belayed, imagining how sweet this would be on harder snow or ice. Nearly at the end of the pitch and a short distance from placing something more reliable in solid rock, the soft snow at the top of the headwall suddenly broke away from the crest. It didn't look like much at first, just a benign pile of slush creeping slowly down slope, but it rapidly gained momentum, transforming simultaneously into a dangerous slide as I screamed "AVALANCHE!" Brian saw for a brief moment what was coming before it knocked him backwards, sending him cartwheeling down the fifty-degree slope, a blur of red fabric, yellow boots and swirling snow. The dubious picket placements never stood a chance, and standing at the belay I was helpless to do much more than watch while he tumbled past, bouncing off some rocks on his way to the glacier basin below. I feared for the worst, yet miraculously he was alive although firmly cemented in the wet snow. His cries for help confirmed he was alive, though not too happy with his situation, trapped in the middle of a major debris zone. Yet, by the time I reached him he had nearly extricated himself, though was in obvious pain and in shock. Chris and Dave joined us soon after, having heard us from below, and after assessing Brian's condition we all retreated immediately to base camp. Surprisingly, he had sustained no life-threatening injuries and was capable of descending unassisted. We arrived back in base camp a few hours later.