Structures

Geological structures, such as jointsJoint, folds (including anticlinesAnticline, monoclinesMonocline and synclinesSyncline), faultsFault, and domes, are highly important in determining the role that rocks play in landform development. JointsJoint are a type of rock fracture, which unlike a faultFault, show no evidence of movement on either side. JointsJoint can be formed by a number of factors, including tectonic stresses, changes in the temperature of a rock mass, and release of pressure by erosion of overlying rocks (unloading). Folds are structures that originally were planar, like a sedimentary bed, but which have been bent by horizontal or vertical forces in Earth’s crust. FoldsFoldmountain can occur at scales that range from mountain ranges to small crumples only a few centimetres long. FaultsFault are breaks in the surface rocks of the earth’s crust as a result of sudden yielding under unequal stresses. Faulting is accompanied by displacement along a fault plane. There are also many different types of igneous massesIgneous mass. Some are very large and are known to have sizes up to 1600 × 160 km. The scale can decrease down to that of a volcanic plugVolcanic plug eroded out from its surrounding ashAsh beds. Some are intrusive and some are extrusive. The former are rocks which cool and solidify within the crust, whereas the latter are those which are poured out on to Earth’s surface. Among the consequences ofSalt (halite)dome intrusion are domes, dykesDyke and ring structures. Some other distinctive structures are associated with rocks composed of salt (halite).