HORST AND GRABEN

elongate fault blocks of the Earth's crust that have been raised and lowered, respectively, relative to their surrounding areas as a direct effect of faulting. Horsts and grabens may range in size from blocks a few centimetres wide to tens of kilometres wide; the vertical movement may be up to several thousand feet. They are bounded on both sides by steeply dipping normal faults, along which movement has been essentially equal, resulting in blocks that are scarcely tilted. The faults forming horsts generally dip away from each other: those forming grabens generally dip toward each other. Two or more horsts and grabens may occur adjacently. They are thought to be due to lateral tension possibly produced by regional uplift or salt dome formation; they often occur on the crests of domes or anticlines. Valleys formed in grabens are commonly called rift valleys and may exhibit features of vulcanism often associated with graben formation. Examples of grabens are the JordanDead Sea depression and Death Valley. The Vosges Mountains of France and the Palestine Plateau are typical horsts.