I had a similar situation over the weekend. I'm fermenting in 7.5 gal plastic bucket. Pitched the yeast Saturday afternoon and noticed a little foam coming up the airlock last night. This morning I woke up to find the airlock blown off and a large mound of foam coming out the hole. I'm hoping it settles down today and it still turns out okay, on the plus side it is smelling very good. My question is, what causes this to happen and what can I do to avoid this in the future.