Shot this today with my telephoto across the dog park. This younger rider, must have been 16 or 17, was getting great air over the jumps. He's probably a solid ten feet off the ground here.
As an aside, I found out that one of my teacher's teenaged sons was practicing his jumps at the Polo Grounds where this shot was taken. He crashed very, very hard. He was wearing a helmet but not a full face MX style helmet and smashed his face into his handlebars causing massive bruising but did not, apparently, break any bones.
Unfortunately though, he hit hard enough to cause permanent damage to one of his ears and has since gone deaf on one side of his head.
The bottom line is, if you're going to launch yourself ten, twelve or more feet in the air, wear as much protective gear as you can possibly muster.