GEOG M109 Lecture Notes - Lecture 6: Permafrost, Pore Water Pressure, Lithology
Document Summary
Land subsidence is the surface sign, and the last step, of a variety of subsurface displacement processes. Land subsidence is a gradual settling or sudden sinking of the earth"s surface owing to subsurface movement of earth materials. Tectonic movement, compaction, drying-up of lacustrine basins, oxidation of highly organic soils, karst cavern collapse, thermokarst depression. 50 land subsidence collapse/year by natural causes. The transfer of subterranean fluid (oil fracking, water pumping for irrigation); removal of solids (soil/coal/mineral ores, salt, sulphur); disruption of permafrost; compaction and reduction of sediments. 2000 land subsidence collapse/year by man-made activity. Land subsidence will occur only where the deposits involved are mostly composed of unconsolidated sediments of high initial porosity. Almost all the subsiding areas are characterized by underlying semi- confined/confined aquifers made up of sand/gravel of high permeability and low compressibility, inter-bedded with layers of clay/silt of low vertical permeability and high compressibility (aquitards).
