I think it is clear what happened here. As the skiier was enjoying a good solid few inches of pow he got caught up in the moment. As he drifted in and out of consciousness, his snowboarder friend stopped, completely blocking the narrow trail. When the skiier looked up, it was too late. He had no choise on such tight a run other than to ram his friend and hope for the best. Upon impact, the skiiers side mounted gopro was knocked off due to force. As the skiier's impact pushed the snowboarder down the mountain things got nasty. At 10 seconds we can observe the boarder's avalanche awarness take effect. He pulls his air bag pack and proceeds to roll down what one gaper may call the "backcountry". At this point the video cuts out and no further conclusions can be made