Snowmobiler triggered avalanche size 2-3

Sledding most of the day, few snowboard runs, backcountry south of Panorama Ski Resort, in the Purcells. We tried to play safe, avoiding steep and convex slopes as much as possible. I mean as much as possible. Riding east facing slopes most of the day, with not much sun exposure on the slopes. At the end of the day around 3pm, we moved to another bowl, mostly south facing. With the snowmobile, my friend went pretty high reaching the summit in the alpine, high marking. Then a big fracture occurred, causing a 20-30 cm slab. Myself and the 2 other friends at the bottom quickly went to a safe spot. No one got hurt. Scary event.