They don't have it in boxes. There are also no guardrails. You might be looking at the conveyor belt in the picture with trees. That's not the Bou Craa belt.
Check out this video of a 10.5km limestone conveyor belt in China [0]. Notice the rollers have a tilt to them? I found a better photo of the belt itself on PBS. [1] if you look on the left hand side of the photo you can make out a cylindrical object beneath the belt. That is the roller, it has the a tilt to it, just like the Chinese belt. Any vibration will result in the load gathering toward the bottom the the belt. Most of what we see on the ground is small particles that are swept off of the belt by wind (Used to live near a port and a concrete factory. Lovely air quality, S&W Ready Mix.)
Check out this video of a 10.5km limestone conveyor belt in China [0]. Notice the rollers have a tilt to them? I found a better photo of the belt itself on PBS. [1] if you look on the left hand side of the photo you can make out a cylindrical object beneath the belt. That is the roller, it has the a tilt to it, just like the Chinese belt. Any vibration will result in the load gathering toward the bottom the the belt. Most of what we see on the ground is small particles that are swept off of the belt by wind (Used to live near a port and a concrete factory. Lovely air quality, S&W Ready Mix.)
[0] http://youtube.com/watch?v=Iq5TN_H_C4o
[1] http://www-tc.pbs.org/prod-media/newshour/photos/2012/12/21/...