Volcanic Chimney?

It looks to me as if you may have had a slow smoldering fire last time or maybe
you wood was alittle damp on the last burn. Looks as if it's just dry soot from the previous
burns. Burning a good hot fire just cleaned out your system...Humidity in the pipe will loosen up
that soot biuld up and when your burn your next hot fire, it blows it right out. :cheese:

The black all over on and around the cap on the pipe = wet wood, or too slow of a smouldering burn.

Never seen all the ash on the ground like that but it is probably creosote produced from what I said above.

just another theory, but what did you do? suck a sheet of burning newspaper up the flue???

I'm not sure that you didn't have a chimney fire. In any event, clean and inspect the entire flue before you start burning again.

I have noticed that burning a couple sheets of newspaper to prime the system at start up will lead to some fluffy flakes in the snow, and there is usually a bit of fly as in the snow here and there, but not to the extent and small size that is all over you deck. Out of curiosity is you chimney that is discoloured at the top like that all the way around, or is the view we are seeing on the leeward side. My outside chimney is like that on the leeward side from smoke eddying around, cooling and condensing. (also I have noticed this on others in the area). when was the last time you put a brush through the pipe (must be a bit of of a bugger with those offsets)?

I see the same thing sometimes on my deck.
I investigated and found my chimney cap was full of the crap.
It has to be smoldering fires-creosote.
I cleaned my chimney not to long ago, and after I come home in the day, and the girlfriends been burning I see it.
Hotter burns will stop that from happening