The reason for cutting slits in top of bread

Hi,

Been quite awhile since I was here but I need some tips. I made a loaf of sourdough bread today. Last time I made the recipe I made them as round free standing loaves and cut the necessary slits in the top of each load. Loaves came  out beautifully.  Today I dedcided to use a loaf pan for my sourdough bread and I forgot to slit the top of the loaf before baking. After the first 10 minutes or so I looked thru the oven glass and found not only had the bread risen the usual extra rise from the heat but one side of my loaf had busted out at the seam. Could it be the reason be that I did not cut the  slits for gases, etc to escape? or Could it be some other reason?

Thanks in advance for any respone.

Doug Mathis