This makes perfect sense, and it makes perfect sense why it causes less turbulence as well, the answer is fluid Dynamics.<br><br>Normally, because a screw is moving, it acts like a wedge. When you push a wedge into something, it moves it sideways, and a screw is a very long wedge. Usually the screw has to be very close to the edge, because if the stuff has somewhere to go, it won't go up as much, it'll just spend it's energy rotating. But when you move the CASING then all the outside particles want to move with the casing, and because the wedge is stationary, they are pushed up the wedge, instead of the wedge pushing them up.<br><br>This is essentially a pump, because you have fluid pressure at the bottom, and then you use a scoop to force it to go into a smaller area, and the pressure increases. As long as the pressure the scoop generates is greater than the pressure from all the sand above it, it will continue to push sand upwards.