Crash after loading world

Put the summary of the bug you're having here

What I expected to happen was...:
My world would load.

What actually happened was...:
It began to load, framerate dropped to one frame every several seconds, then it eventually crashed

Steps to Reproduce:
1. The world was a tunnelers dream superflat with a large minecart roller coaster and it was snowing. I have no clue which of those things made it crash. Could have been all of them.