Screen cracked through the middle, when touched there's waves?

This morning when I got to school, I went on my phone and noticed there's a GIANT crack right through the middle of my phone. It's not too deep but when I touch it I can see some sort of waves near the crack. I'm not concerned about the phone as I'm getting a new one and I have my Mac and iPad to substitute for a while, but why is there waves showing up on my screen? I'm not sure how else to describe it, but it's like when you touch a non-touch screen computer screen and you see waves around your finger. Phone still works, slow as usual, the screen is just a bit weird.