Theory question 306
Earth Movements and VulcanicityWith the aid of diagrams, describe the mode of formation of the following features: (a) stack; (b) fold mountain.
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(a) Stack: waves attack a headland of resistant rock along joints and faults by hydraulic action and abrasion; caves form on both sides of the headland; the caves meet to form an arch; continued wave attack and weathering make the roof of the arch collapse, leaving a pillar of rock standing in the sea: a stack (later worn down to a stump). Diagrams: cave, arch, stack.
(b) Fold mountain: sediments accumulate in a geosyncline (sea basin) between two land masses; earth movements push the land masses together (compressional forces, plate convergence); the layers are squeezed and buckled into anticlines and synclines; continued compression produces overfolds, recumbent folds and nappes, raising high fold mountains, e.g. Alps, Himalayas, Atlas, Andes. Diagrams: before and after compression.
Draw the stages in order.