EARTHSC 2GG3 Lecture Notes - Lecture 13: Subsidence, Gypsum, Clay Minerals
6 May 2016
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Document Summary
Types of ground movement: ground movements are not as dramatic as earthquakes or volcanoes, but cause far more monetary damage, deform and effectively destroy roads, utility lines, homes, other structures. Sinkholes form when overlying ground collapses into underground cavities. Land subsidence occurs when sediment becomes more closely packed, through groundwater or petroleum extraction, or earthquake shaking. Swelling soils form from alteration of volcanic ash to clays: sinkholes. Ground may suddenly collapse into sinkholes tens to hundreds of meters across. Some common sedimentary rocks are soluble in water (salt, gypsum, limestone, other carbonates) Areas with underlying limestone can have caves, springs, streams that sink into ground, sinkholes. Caverns form where carbonate rocks near water table dissolve in groundwater. Roof of cavern collapses if left unsupported where water table has dropped. Limestone dissolves in slightly acidic rainwater, at rate of millimeters per thousand years.
