Large holes in landscape when disconnected.

Not sure where to report or to get help at. While playing Mindcraft, a couple of times my computer has been shut down due to power outage in the area while playing. So I don't get a chance to save the game or time I was playing. That doesn't seem to bother, but there is one big problem when it has happen. When I log back on there are now large dug out holes ranging able 15x15 block, but it goes deep. So deep there is no bottom. I can't go into that area, but when it happened a second time I tried jumping into it to see what happens. Now I'm in a hole I can't get out.

Is there a way to reset, without losing all the long hours spent building and doing the work I have done to the world I'm in? I mean I spent a lot of time doing things and collecting items. It happened a long time ago, but I never reported it. I just gave up and stopped play for a while cause I really got bummed out. Lost some much work. I hope it's not going to happen again....... can you help?