Trigger is not confirmed but very much appears to be a snowmobile triggered avalanche judging by the tracks. There is a slight chance that after the riders were on the slope, it released naturally later on with additional wind loading. However, the tracks and the debris appear to have about the same amount of wind drifted snow on them. My money is on a sled trigger.
These avalanches are now to the point where they are very dangerous. We finally have added enough snow to them where they are breaking to the ground.