GEOG 1350 Lecture 6: Subsidence
2 Dec 2017
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Document Summary
Definition: nearly vertical downward movement of earth"s surface. The speed of subsidence can vary from very slow to rapid. The subsiding area can be a variety of shapes. It is not usually life-threatening but is one of the most widespread and costly hazards. It is often associated with the dissolution of limestone, marble or gypsum. Other causes: thawing or frozen ground, compaction of sediment, shrinking of expansive soil, earthquakes, deflation of magma chambers. It results from the dissolution of rock, some rocks dissolve in the vicinity of water. Karst is most evident in area 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 1 cm per decade.
