They use the machine you see above. It’s called a Pipe Monster, and is made by a Swiss company called Zaugg. It’s used in all major events, like the X-Games, the Olympics, the U.S. Open of Snowboarding, etc. And it ensures that the half-pipe that is created is uniform and standard. The process goes a little like this: first, other machines make a giant snow bank. Then the Pipe Monster is called in.
“Its 22-foot arm features a bunch of augers that go into gearboxes which connect. The snow it chews travels down the arm and into a blower that allows you to control where you want the snow to be ejected (including in front of the vehicle, in the off chance that you need to fill in a hole). [The machine] is powered off of a single hydraulic motor and it’s able to cut up to 25 feet of 18 or 22 foot pipe per minute. It weighs 3250 pounds and attaches to the front end of a snow cat.
After multiple passes, you have a perfect half-pipe. When it’s been used up a little, the Pipe Monster makes another pass, smoothing it down, but in the process making the two banks a little further apart. The angle and height remains the same, but the flat part in the middle gets progressively larger as the competition drags on.
And now you know.