Lava Flow

An expression that describes a morbidly obese person's rolls of fat, usually, but not limited to, the torso of their body. Typically, these rolls of fat are spilling over pants, shirts, or any other articles of clothing, resulting in a visual analogy to lava flowing over a wall, embankment, or into a body of water.

"Oh my, look at that person's lava flowing over their pants!"
Or, "Holy crap, that person is so fat, its like lava flow!"