I build snow jumps every year. The key is to form them so you dont use alot of snow. Last year I had this raised area that I tore down and got some huge snow chunks out of there and set them on top of my existing jumps, threw a bunch of snow on it all, put water on that and raked it out. It is easier to take up the space under the jump with hay bails or anything else, but they will definately not fall apart if they are just snow. Good luck, I will have epictures of mine up in the next month when we start getting snow.
It is easiest to use a snow blower, I literally snowblew my whole yard last year to make jumps. Pile stuff up and blow snow all over it, rake out the snow a bit, wait a few hours for it to start to freeze, put a few coats of water on it and use a leaf rake to rake it which makes it have tons of traction. If you follow those steps, you will have a rock hard landing or jump.
I built this one at the end of last season and never got to hit it, I had the other jumps back farther, you can kind of see them but they are really small because we were already tearing them down. When I was building that big jump the snow was kinda wet and I had a few big pieces of plywood I used to form it.
