In work that I've been doing, we've come across an interesting problem. In a manufacturing process, a highly viscous, non-Newtonian fluid goes down a vertical chute and then gets pushed horizontally out the bottom by some rotating screws. Sometimes, the fluid gets pushed out the bottom, but the fluid in the chute doesn't continue to come down. The company that has this problem calls it 'bridging' where you essentially get a little cave at the bottom, the 'bridge' forming the roof and preventing the fluid from continuing to come down. I would like to know more about this. Does anyone know what this type of phenomena is called and where I might look to learn more about it?