my ipod freezes then crashes whenever i play games such as Asphalt 8

my ipod freezes, lines show up on my screen, then the whole thing crashes like its restarting. this happens when I play games like Asphalt 8 and Angry Birds Go and it has also happened on safari. it has been happening for a week now. it does this when i'm on it for at least an hour more or lees

please help