The miner operator on the east mains, left section, MMU 007-0, received fatal crushing injuries when portions of the right rib and corner fell unexpectedly. This occurred suddenly while the miner operator was cleaning the second cut in the 5 to 6 crosscut. The rib anomaly was approx 8.5' X 4.5' X 4.5' in the 5 to 6 crosscut and fell pinning operator against shuttle car.