You said the crack was in the bark. If it is only in the bark, and not through the cambium, it is just the tree maturing. However, two inches is a bit much for one year, and I suspect you have the beginning of a seam starting into the wood. It will be on the south side of the tree, more than likely, and is caused by the sun's heat working with the freeze-thaw cycles in February and March.
There's not much you can do - red maple are prone to this, and at least half of my red maple here that are somewhat open-grown (trunks exposed to the sun in Feb) have these seams. As a general rule, they do not weaken the tree significantly. I have seen many branches fall from red maples on account of poor branch development, but I can't remember one trunk failure because of a seam. I have seen them grow closed too. Takes many years though.
