GEOG 1350 Lecture 6: Geography 1350 6th Lecture
9 Dec 2018
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Document Summary
Definition: nearly vertical downward movement of earth"s surface. The speed of subsidence an vary from very slow to very rapid. The subsidising area can be a variety of shapes. It is not usually life-threatening but is one of the most widespread and costly hazards. Subsidence is often associated with dissolution or limestone, marble, or gypsum. Other causes: thawing of frozen ground, compaction of sediment, shrinking of expansive soils, earthquakes, deflation of magma chambers. Some rocks dissolve in the vicinity of water. Karst is the most evident in areas of limestone because this is the most common of the dissolving rocks. Water containing carbon dioxide is acidic and thus aids in the dissolution process. Chemical reactions leading to dissolution: water + carbon dioxide = carbonic acid, carbonic acid + limestone = calcium carbonate. Limestone dissolution can result in the lowering of a surface by 1cm per decade. The process produces empty voids over a range of sizes.
