Big air pocket in my sourdough loaf.

Big air pocket in my sourdough loaf.

Hi all, I am having an issue with my sourdough lately.I am hoping someone can give me some advice on how to fix the problem. I am getting a huge air pocket in my loafs, it is from the top crust down to the middle 

any help would be great.

Thanks, wristen

Source: Fresh Loaf