Snyper is correct, in that the action has loosened up in the bedding, and firing has caused the split. I would see about epoxy bedding it, and fixing the crack in the process.
The crack can be fixed, by allowing some thin slow-setting epoxy to run in or be injected into the crack, then you pull it together with some surgical tubing, etc. until it sets. Another way to clamp it is to use a piece of thick belt leather, and wrap that around the stock, leaving about a 1/2" wide opening at the crack, in the leather. Wrap a piece of iron stovepipe wire around the leather, then twist the wire, which will draw the crack tight on the epoxy.