The Geochemistry of the Solvent:
The influence of the solvent in the Greenbrier Valley karst system is similar to Mammoth Cave area which involves karst development by epigenic process. The Great Valley is both by epigenic and hypogenic processes, but there is debate on epigenic versus hypogenic in the maze caves in southwest Virginia in Devonian units (Palmer, 2009). How much cave development is epigenic versus hypogenic is a debate especially outside of the Greenbrier Valley karst.
- Epigenic means that the caves are formed by acid creation that occurs at or near the surface of the Earth. Hypogenic processes involved processes of dissolution that come from below, usually sulfuric acid (Palmer, 2007).
- Dissolution in the Great Valley started from dissolution well below the water table, but as erosion as exposed more of the karst surface epigenic processes can also contribute to dissolution from above. There is debate in the Great Valley and especially in caves with maze morphology on whether or what level hypogenic dissolution influenced cave development.
- Geochemical conditions in the Laurel Creek Cave area which is part of the Greenbrier Karst group were attributed to mass transfer on Calcium mostly, but with small concentrations of Magnesium ions into Laurel Creek (Groves, 1997). In the Great Valley area where is more dolomite you would expect to see some more Magnesium Ion concentration in solution.
Hydrological Variables:
- Structural Controls exert a major control on the hydrology especially in the Great Valley which includes things like such as; residence times, discharge, location of recharge points, location of discharge points, which all can all influence the water chemistry and water management (Doctor et al., 2008; Palmer, 2009)
- Great Valley has more diffuse flow versus the Greenbrier Valley which has more conduit flow (Kozar and Mathes, 2001)
- Recharge points are sinkholes(mostly subsidence sinkholes), sinking streams(in Greenbrier Valley but not as much in the Great Valley), and swallet holes. Discharge points are through springs which are lithological and structurally controlled.
- Ground water occurs moves through fractures of lower permeability areas and then is collected over broad highs or higher permeability that are the major structural features.
- The Hydrological system in the Great Valley is considered to be Anisotropic and not Isotropic. This means that the permeability is greater in one direction versus another and not equal permeability throughout. These form caves that are typically maze like caves and have an elongate pattern and typically follow the strike of the strata (Palmer, 2009).
Discharge values from (Kozar and Weary, 2009) at Opequoun Creek in northeastern West Virginia and far western Virginia include:
- 390 mm/yr in an area where intensive downcutting by the Potomac River takes place and has a higher density of cross-strike faults
- 280 mm/yr for carbonate formations in the Great Valley
- 150 mm/yr when underlain by the shales of the Martinsburg Formation
Hydraulic Conductivity Values for two lowest values:
Martinsburg Formation: 0.6 m/d
Conococheague Limestone: 0.8 m/d
- Values can go up to 120 m/d due to fractures along major fault zones. Especially cross-strike faults and some oblique faults.
Hydrology in Relation to Cave Development:
- Cave passages in the Great Valley are commonly phreatic, lack sinking streams, and contain sediment filled passages. This signals the development of karst passage well below the karst table that is now being exposed closer to the surface by deep seated (hypogenic) processes are now being exposed due to erosion, which is leading to more epigenic processes (Doctor et al.,2008 ).
- Cave passages in the Greenbrier Valley are both vadose and phraetic. These caves are interpreted to be more epigenic in nature. Recharge can be from sinking streams, swallet's, or sinkholes.
Concerns:
- The Shenandoah Valley which is the eastern extent of the Great Valley is experiencing population growth and is located along the I-81 corridor. Because of this there is an enhanced concern for groundwater pollution.
- Pollution sources include agricultural runoff, industrial pollution, landfills, septic tanks, or any other underground storage tanks (Orndorff, Harlow, Jr., 2002)
- The Great Valley contains a significant amount of regolith (10 meters thick or more), can cause for water and pollution to be stored especially if the pollution source is being spilled over an extended period of time (Doctor et al.,2008 )
- Also sinkhole development is a concern in this area especially adjacent to any structural features such as folds, faults, or joints.
The influence of the solvent in the Greenbrier Valley karst system is similar to Mammoth Cave area which involves karst development by epigenic process. The Great Valley is both by epigenic and hypogenic processes, but there is debate on epigenic versus hypogenic in the maze caves in southwest Virginia in Devonian units (Palmer, 2009). How much cave development is epigenic versus hypogenic is a debate especially outside of the Greenbrier Valley karst.
- Epigenic means that the caves are formed by acid creation that occurs at or near the surface of the Earth. Hypogenic processes involved processes of dissolution that come from below, usually sulfuric acid (Palmer, 2007).
- Dissolution in the Great Valley started from dissolution well below the water table, but as erosion as exposed more of the karst surface epigenic processes can also contribute to dissolution from above. There is debate in the Great Valley and especially in caves with maze morphology on whether or what level hypogenic dissolution influenced cave development.
- Geochemical conditions in the Laurel Creek Cave area which is part of the Greenbrier Karst group were attributed to mass transfer on Calcium mostly, but with small concentrations of Magnesium ions into Laurel Creek (Groves, 1997). In the Great Valley area where is more dolomite you would expect to see some more Magnesium Ion concentration in solution.
Hydrological Variables:
- Structural Controls exert a major control on the hydrology especially in the Great Valley which includes things like such as; residence times, discharge, location of recharge points, location of discharge points, which all can all influence the water chemistry and water management (Doctor et al., 2008; Palmer, 2009)
- Great Valley has more diffuse flow versus the Greenbrier Valley which has more conduit flow (Kozar and Mathes, 2001)
- Recharge points are sinkholes(mostly subsidence sinkholes), sinking streams(in Greenbrier Valley but not as much in the Great Valley), and swallet holes. Discharge points are through springs which are lithological and structurally controlled.
- Ground water occurs moves through fractures of lower permeability areas and then is collected over broad highs or higher permeability that are the major structural features.
- The Hydrological system in the Great Valley is considered to be Anisotropic and not Isotropic. This means that the permeability is greater in one direction versus another and not equal permeability throughout. These form caves that are typically maze like caves and have an elongate pattern and typically follow the strike of the strata (Palmer, 2009).
Discharge values from (Kozar and Weary, 2009) at Opequoun Creek in northeastern West Virginia and far western Virginia include:
- 390 mm/yr in an area where intensive downcutting by the Potomac River takes place and has a higher density of cross-strike faults
- 280 mm/yr for carbonate formations in the Great Valley
- 150 mm/yr when underlain by the shales of the Martinsburg Formation
Hydraulic Conductivity Values for two lowest values:
Martinsburg Formation: 0.6 m/d
Conococheague Limestone: 0.8 m/d
- Values can go up to 120 m/d due to fractures along major fault zones. Especially cross-strike faults and some oblique faults.
Hydrology in Relation to Cave Development:
- Cave passages in the Great Valley are commonly phreatic, lack sinking streams, and contain sediment filled passages. This signals the development of karst passage well below the karst table that is now being exposed closer to the surface by deep seated (hypogenic) processes are now being exposed due to erosion, which is leading to more epigenic processes (Doctor et al.,2008 ).
- Cave passages in the Greenbrier Valley are both vadose and phraetic. These caves are interpreted to be more epigenic in nature. Recharge can be from sinking streams, swallet's, or sinkholes.
Concerns:
- The Shenandoah Valley which is the eastern extent of the Great Valley is experiencing population growth and is located along the I-81 corridor. Because of this there is an enhanced concern for groundwater pollution.
- Pollution sources include agricultural runoff, industrial pollution, landfills, septic tanks, or any other underground storage tanks (Orndorff, Harlow, Jr., 2002)
- The Great Valley contains a significant amount of regolith (10 meters thick or more), can cause for water and pollution to be stored especially if the pollution source is being spilled over an extended period of time (Doctor et al.,2008 )
- Also sinkhole development is a concern in this area especially adjacent to any structural features such as folds, faults, or joints.