Paleocollapse
Encyclopedia
Paleocollapse is a rock structure resembling the karst
landform, but is formed essentially by the dissolution of underlying sedimentary rock
. It has also been called paleo-karst collapse. , . This has the effect of collapsing the formerly intact rock above, forming extensive fractures, debris pipes, and open caverns. Normally, the process was started and completed in the geologic past.
The mechanism of its formation is relatively simple. As in the illustration, a deeper layer of salt
(or other evaporite
) is dissolved, through some process. The support for the upper rock vanishes, and starts the collapse process. This is much like the subsidence associated with old coal mines. Eventually, the caving process reaches the surface, and can be associated with debris pipes, rock fractures, and open caverns. At some later date, undisturbed sediments, or glacial till may fill the collapse zone.
Paleocollapse geology can be remarkably stable (unlike karst), but poses some serious challenges to engineering
or environmental geology
. Primarily, the collapse zone is extremely permeable
. This can provide a conduit for groundwater, or contaminant transport . As well, these zones may only be marginally stable, in that they can be reactivated by human activity, or events such as earthquakes. In China, underground mines have become suddenly flooded, due to paleocollapse features.
In order to fully characterize the hazard, investigations may be undertaken, using dye tracers, or exploration geophysics
. Of particular importance is understanding the true stability of the region. The paleocollapse process may continue at some future date, due to deep groundwater flow changes. Or perhaps, the reason that a certain evaporite zone has dissolved, is because of underlying faults in the bedrock.
KARST
Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...
landform, but is formed essentially by the dissolution of underlying sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
. It has also been called paleo-karst collapse. , . This has the effect of collapsing the formerly intact rock above, forming extensive fractures, debris pipes, and open caverns. Normally, the process was started and completed in the geologic past.
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
(or other evaporite
Evaporite
Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...
) is dissolved, through some process. The support for the upper rock vanishes, and starts the collapse process. This is much like the subsidence associated with old coal mines. Eventually, the caving process reaches the surface, and can be associated with debris pipes, rock fractures, and open caverns. At some later date, undisturbed sediments, or glacial till may fill the collapse zone.
Paleocollapse geology can be remarkably stable (unlike karst), but poses some serious challenges to engineering
Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
or environmental geology
Environmental geology
Environmental geology, like hydrogeology, is an applied science concerned with the practical application of the principles of geology in the solving of environmental problems. It is a multidisciplinary field that is closely related to engineering geology and, to a lesser extent, to environmental...
. Primarily, the collapse zone is extremely permeable
Permeability (fluid)
Permeability in fluid mechanics and the earth sciences is a measure of the ability of a porous material to allow fluids to pass through it.- Units :...
. This can provide a conduit for groundwater, or contaminant transport . As well, these zones may only be marginally stable, in that they can be reactivated by human activity, or events such as earthquakes. In China, underground mines have become suddenly flooded, due to paleocollapse features.
In order to fully characterize the hazard, investigations may be undertaken, using dye tracers, or exploration geophysics
Exploration geophysics
Exploration geophysics is the applied branch of geophysics which uses surface methods to measure the physical properties of the subsurface Earth, in order to detect or infer the presence and position of ore minerals, hydrocarbons, geothermal reservoirs, groundwater reservoirs, and other geological...
. Of particular importance is understanding the true stability of the region. The paleocollapse process may continue at some future date, due to deep groundwater flow changes. Or perhaps, the reason that a certain evaporite zone has dissolved, is because of underlying faults in the bedrock.