First falling waterdrops were still in the air when water suddenly froze, not everywhere, just in some places, probably in one biome of the two:
On the surface the hell of a mess of ice, water, magma and obsidian is forming:
It grows:
An icy wall grew up near the edge of the map:
One flying glass leaf, damaged by falling ice, is leaking. Big icy things hang in the air not falling, I have no idea what the fuck is going on:
In the end of July all the water froze, hanging icy things finally fell. Flying deck's obsidian foundation got transparent where ice has formed over it:
Miners tried to dig out the ice that has been formed over the flying deck. When they finished any stripe of ice, strange thing happened: the obsidian foundation beneath the entire stripe suddenly collapsed, obsidian blocks fell on the ground, ice boulders disappeared but the ground where the blocks fell over, got covered with ice:
Dwarves built an outside mason workshop to make ice blocks, I didn't know that it's techically imposible:
Miners also dug out the permafrosted brook. The mysterious virtually solid surface of the brook fell one z-level down, the brook became the underground one. Miners had to pierce its cover with many stairs:
Miners penetrated ice conglomerates with stairs: