dodgy rise?

was it fully proved?

Looks like your slashes solidified, and then the bread started rising, cracked around the bottom, and lost some of its gases. I’d like to see the internal structure if you have the chance to post a picture. It looks like a combination of at least 2 factors, e­.g. oven not hot enough in the beginning (are you baking on a pizza stone or a dutch oven?), perhaps underproven dough, very high hydration, "grainy" flour (not retaining gases), etc. Can’t tell for sure just by looking at the crust like that.

Hi,

I had this happen a couple of weeks ago when I was trying to bake 2 loaves side by side on a stone (happened twice). They blew out between the loaves. I am fairly sure they were underprooved because I was in my usual hurry but what made it worse was that there seemed to be a moist "microclimate" between the loaves so the tops hardened normally but there was a weak spot on each at the adjacent sides that ruptured at about the 15 minute mark. The recipe was my normal one, the difference to normal was that i was going out so tried to hurry things up. The split bread was terrible as there were huge holes inside- just as well the family likes that Italian bread salad that hides any dodgy loaf.