Tree bark splitting
There is nothing you can do about this situation now. It may take a while for the tree to die, so I wouldn't cut it down right away. I would not recommend using gravel mulch in general around plants. Gravel does nothing to enrich the soil and provide organic matter, the way any organic material (like hardwood bark mulch or composted yard waste) does as it decomposes. Also, it looks like the gravel is fairly deep because I don't see a root flare at the base of the tree. That could also be because the tree was planted to deeply 14 years ago. Trees that are planted too deeply or have mulch mounded at their base often suffer.