It looks like a glue line has failed in the riser laminations.
Give Jack a ring, but I'm guessing he'll just run some this CA glue in there (as Rob suggested) & refinish the riser.
With a little patience& common sense, you can do it yourself.
If that's the extent of the crack, I really wouldn't worry about it too much. I had the same exact problem with one of my bows & the bowyer told me not to worry about it (Big name bowyer, PM me if you want to know who) it shouldn't affect the bow at all.