Sudden Airlock Bubbles... Thoughts?

Hi BA HB'ers,

I brewed a stout with an OG of 1.070 and re-pitched slurry of S-04 taken from a 3 gallon batch of brown ale I had brewed previously (1.050-->1.018, yeast kept in fridge about a week). I let the wort chill in a swamp cooler overnight, since the apartment i just moved to is pretty small and i'm still figuring out chilling techniques. When I went to sleep on brew day, the wort was in the mid 80's, and I woke up and pitched first thing in the morning at about 65-66F. There was no airlock activity for about two days, so my first thought was that the yeast was still cold. I took the bucket out of the swamp cooler and i guess the agitation shook the airlock enough and caused a few bubbles, but it just kept going and actually sped up within about ten seconds. I left it out for about a half hour to see if it was just blowing off a little bit of pressure but it just kept firing away, even after I put it back in the swamp cooler, and it's sitting right next to me right now at 68 F, with star san bubbles rising through the holes in the lid of the airlock. I'll add that there isn't a lot of head space in the bucket, as we had almost 6 gallons going into a regular plastic bucket fermentor like the ones that come with starter kits.

I'm just surprised by how suddenly and vigorously this thing started fermenting, and I'm wondering if it's a sign of something specific, and if anyone else has seen this before. Thanks!

 

yeah, i've had beers wait a while to get going, but once they do it's usually at least a little bit gradual. this started going nuts in a matter of literally five seconds, which seemed strange to me.