In next two turns, if i remember corectly ...
Lot of time to rip Tavs head off with last 7HP monster would not have if spell had proper damage rolls.
I'm not certain but I believe the first 1d4 is applied immediately on the creation of the surface and the next one on the target's next round beginning.
It's also annoying if you want to target an enemy that is engaged in melee with one of your allies. The surface will most likely also hit them, making thunder the only viable option in this case unless you don't care about hitting your teammates.
Evocation specialisation should mean your surfaces don't damage allies, really. I wonder if it does.
