why has catterick been abandoned?

Fumigators

Unsafe ground apparently.

ahh cheers, Couldn't find the info anywhere!

Finellas Fortune , who finished second in the 4-20, fell just after the winning post and jockey Andrew Mullen was lain prostrate for a couple of minutes. It appears he was winded but also seemed to have hurt his arm or his wrist. After the race they sanded the area where the horse had fallen, but  a delegation of jockeys and trainers decided that it may have still been unsafe to continue. The stewards were left with no option but to abandon the last two races.