Large avalanche in Cypress backside

There's a hard 5cm thick snow layer underneath 5-10cm of powder. Riding conditions not too great because of the heavy snow. Observed a massive size 2 slab avalanche with one partially buried person, unharmed. Not sure if self or over distance triggered. The top 20cm teared over a width of around 400m, below Mt Strachnan and slid trough the gully.