In geomorphology, the resistance of a rock mass to rupture under stress. Strength varies with, in order of importance: the spacing of joints, the cohesion and frictional force of the rock, the dip of any fissures, the state of weathering of the rock, the width of fissures, the movement of water in or out of the rock mass, the continuity of the fissures, and the amount of infilling of soil within the fissures. See Jackson (2002) GSA Today 12, 9 on the ‘jelly sandwich’ view of the continental lithosphere; see also Townend and Zoback (2000) Geology 28, 5 on the way faulting keeps the crust strong.