EARTHSC 2GG3 Lecture Notes - Lecture 13: Stalagmite, Mining, Permafrost
5 Sep 2014
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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. 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. Slightly faster rate in humid areas sinkholes and caverns more common in tropical climates: air pollution makes rain more acidic, increases rate of dissolution.
