My 7 year old girl threw a huge tantrum recently too. It was very violent and pretty scary!! I read somewhere that, aside from toddlerhood, tantruming can peak again at age seven. It really didn't give an explanation as to why, however, I know that 7 is a big transitional age for many. They are shifting in their consciousness and recognizing themselves as part of the world vs. the center of the world. Puts a lot of pressure on some as they compare themselves to others, see the unjustice of the world around them, feel less important, etc.
So handling tantrums with an older child is similar to how you handle them with a toddler. Safety is priority #1. I actually restrained my dd until I was sure that she wasn't going to come at me or otherwise inflict harm. Also, it is very important to NOT engage emotionally. It is really helpful to remember that people in that heightened of an emotional place can generally not reason through it. This is the hardest one for me to do. Remain present if she seems to need that (at some point I could tell that my presence was keeping her going s0 i left her to deflat). Don't allow the tantruming to dictate your choice (i.e. don't give in).
Then, later, when she is completely calm and removed from the tantrum you could gently discuss temper management. Give her some ideas how to recognise and deal with her anger before it blows into a trantrum. My daughter really recognized how absurd her behavior was and was even embarrassed by it. It didn't ridicule it though. She obviously needed a big release and was really content when it was all over. I "get this" from personal experience. I myself tantrum sometimes. They of coarse are more refined, (usually swear words under my breath or something similar).
Best of luck, it's not easy!