My dough is cracking while it rises.

I think the sponge is underprepared and you have used more water than required for a proper dough. Also it may be overproofing.

I'm wondering if you are letting the dough autolyse long enough and before adding salt.  After first mixing up the dough let it stand covered for 20-30 mins. Autolyse allows for better absorption of water and helps the gluten and starches to align and so help with shaping. After autolyse I usually mix and fold my dough a few minutes in the bowl while I'm folding in  the salt. This helps develop the gluten strands which are the structure of your bread and will help your bread hold it's shape and have more volume. See these links also: 

www.thefreshloaf.com/lessons/tentips_8_autolyse

www.abreadaday.com/

You might also have a look at your slashing method. If you slash long strokes down the length of your loaf then it will naturally spread out even more. Try some more shorter slashes on an angle on either side of the loaf (sort of like gill slits) and slash upwards as this helps it keep the loaf shape.

Lastly, the time between slashing and placing into your oven should be as short as possible. Any dough will spread out after slashing so that is why you need to be quick to get it into the oven.

My experience is that rather than underproofed dough it is overproofed dough becomes too slack and won't hold a shape (Something to do with the enzymes having broken down too much of the starches which are what help with structure).

cheers..Johnny

Many things could have gone wrong. Give as a full recipe and technique so we could decide more accuretly what the problem is.

The gluten in degraded for some reason. Maybe long fermentation and high acidity, maybe the flour is not top quality and has many proteases, maybe your don't develop the gluten correctly, maybe the hydration is too high and you need a good scale... :)

I had this problem reasently and my problem was the flour. When I tried a simple bread flour I had 100% success, but the one I bough that was strong flour from a local mill was always a failure...

 when are you adding your salt? When you see the cracking at the sides during proofing, stick your finger in there and taste to see if it is salty. Could be that the salt is not incorporated enough. At work we call them salt veins. 

Or could just be too acidic.

 To me just guessing and that is all I can do yet ... Is that there are several possibilities.

1- too much starter to dough ratio

2- like Johnny said, autolyse or salt too early

3- over proofed or proved at too high a temp (i guess that might be two different guesses!)

4- too much liquid to dry

5- are you using a lot of rye?  Or Spelt perhaps?

So spill it if you really want us to help.  You've got our attention we need your help now:)

 Okay - Please spill it! We need details :)

I'd suggest first find some very good quality flour, I had a problem recently and it was the flour...though it was strong flour it was from a local mill and full of protease that broke down my gluten.

Then I'd weight my ingredients with a good scale(that weights 1gr) and watch the things millciti says.

 Hope we didn't scare you off!   Actually I think you may have updated your original post explaining part of your process..   I really think the problem is Temp related or your starter is more active than it was to start with, and you may have less than perfect flour.  When you fold and stretch the dough, if your temp is too warm your dough may be developing too much between folds.  This could be allowing too much protease development as Dukegus said.  I found this article at the fresh loaf which is very interesting about the problem and the process...

http://www.thefreshloaf.com/node/12057/sourdough-starter-impairs-gluten-...

When I switched seasons this year going from  cool to toasty I needed to switch up something.  I tried a few different things - different flour combinations,starter hydration levels and amounts.

Try changing one factor at a time taking note of what you try.  See what works and what doesn't.  What worked for me was a combination of less starter and a higher hydration starter I went from 75% to 100% mostly.  I have 2 starters.  Also another thing that I am doing right now is shorter stretch & fold times, a short rise in the bowl, form loaves and another short rise and overnight proof in the banneton in the Fridge. The whole process is under 12hours.  With the heat in full swing here I set the timer and pre-start my oven in the morning and bake before work.

I actually refresh my starter when I bake and store in the fridge - less than 12 hours on the counter.  Then I warm it up for an hour or so before I bake.  But I bake every other 1-2 days, so my starter is still very active.

This was this mornings bread... Hopefully will post picture later.

Terri

 Just looking at your pictures I notice that while your dough looks mixed - It just might not be mixed enough.

You kneed (pun intended) to kneed it well to let the gluten do it's job.

While saying that - if you have mixed it cotrrectly then it might be that your flour is inferior.

Looking at your baked photo.... It looks like it has overproofed. Too much steam/ humidity while prooving.

It almost looks like it collapsed while baking. 

If you do not have the luxury of a proover and the humidfying elements then I would definatly say that it's flour problem.

And maybe just a tad too much water.

Please consider all before me. Their comments bear great weight.

Just a matter of elimination my dear Watson.

I was getting something very similar when I was turning out my dough from the banneton just before baking. A shorter ferment time solved the problem for me. I was fermenting for 4 hours before placing in the refrigerator. Going to 3 hours was all it took. 

below is what I was getting:

farm8.staticflickr.com/7141/6413658275_da13ef56f4_z.jpg

Good luck!

what humidity are you proving the bread at?

is the surface tending to dry out?