Can I request a change of custody if my ex leaves the state without notifying me?

We were divorced in 2007 with Joint legal and joint physical custody. I initially (with my ex's help) moved with the kids from Utah to Alabama in 2007 for two reasons: she was stalking me, and I got married. She continually harassed me- tried to break into my car, my house, tried to get me fired from my job, and she attacked me in front of the children (she was charged and convicted for domestic violence for that one). She has been in contempt of court at least 3 times over my custody rights. The day I left the state, she applied for child support- even though I had the kids. My ex refused to sign any paperwork, so the state attorney got involved in the case, and I voluntarily agreed to return the kids to Utah. I have summer visitation, fall break, Christmas break, spring break, and phone calls. She has had half dozen boyfriends since that time. The kids get carted off to grandma's house or their aunt's house every weekend. I'm pretty sure for the last 3 months they have all been living with grandma. Last year, she taunted me and said that she was moving to the Marshall Islands to be a massage therapist. She threatens me all the time that she is going to move, and I'll never see the kids again. My kids (10 & 11) are close to their cousins and extended family. Yesterday, my kids called and stated that they are moving to Ohio (they called from the Interstate, and said they are already in Ohio). She had a fight with her mom about paying the utilities, got a new boyfriend, and he has a job in Ohio apparently. She did not give any notice. Her family has a history of bipolar disorder and depression. Upon divorcing me, she disappeared for 6 weeks. From bank account records, she went to NY, TX, MI, WY, AZ with her boyfriend (a trucker). Even though the kids will now be about 8 hours away (instead of 27), I feel this is very unstable for them, based on her history. Obviously, this is the barest of details, but could this finally be the grounds for custody.