Hey folks, armature baker here. I've been staring out with sourdough bread. My first two attempts have been coming out weird like the picture I've attached. I usually let the dough proof for 4 hours at room temp. then i leave it in the fridge overnight to proof longer. I then take it out and place in the oven. Would appreciate any feedback as to why the bread is coming out like this?
Cheers! 
Crust has formed too quickly and the gas needs to escape so it takes the easiest route which is now anywhere but the top. That and possibly some under proofing will cause blowouts.
Answer will be steam and perhaps longer proofing so it doesn't have runaway oven spring.
Brilliant, thank you for the feedback!
I think this problem is with shaping. Your loaf probably was very weak on the bottom.
Me Likey, you may have come up with a bread that will replace the Open Crumb craze with a new age chic abstract art bread. I can only try to imagine the skills necessary to produce such a masterpiece. LOL
It might make a great ladies hat for the modern woman ;-)
Apart from Abe’s guess, I can’t imagine how this came to pass.
Dan
A thought - did the bottom of the dough have any floured flaps and/or large creases that could have separated during the bake?
Abe's comment is spot on. The lack of steam is not only apparent in the way you loaf is setting on top and blowing out on the bottom but also by the dull look of the crust. With the right steam your crust should take on a little shine and perhaps some blistering.