Sudden, often explosive, breaking of rock walls when stressed beyond their limits. It is a hazard encountered in some deep mines (below 1000 m), and may be accompanied by shocks, rock falls, and air concussion. It usually occurs in rocks having high elasticity and strength, so that when a face is exposed the unbalanced stress is great enough to cause failure. It can be controlled by systematic stoping, reduction of open spaces, use of strong supports, and retreating mining methods.