Large avalanche full length of slope

Witnessed a group of 6 that triggered a large avalanche. North aspect. I approached the group asking if they needed help while they were probing the debris. No injuries and only 1 buried to the neck. As seen in pictures, an obvious large crown with skier tracks leading to the trigger. Only a ski was lost apparently. I skied a different slope. No evidence of any movement but plenty of surface sluff. Chose more coverage and trees over an open heavily wind loaded slope