Karst
What is required to develop a karstic cave system?
1. Lithology: Strong and pure rock: remain as rook of passageway. No buildup of insoluble material 2. Rock structure: ways by which groundwater can penetrate rock 3. Supply of water and sufficient topographic relief to generate a hydraulic gradient - determines the overall orientation of a cave
2 Classifications of karst Landforms
1. Surface features 2. Substrate features
2 Factors that determine the amount of CO2 in solution
1. Temperature 2. Partial pressure
How much of the Earth's mass does karst landscape cover?
12-15%
About ____% of the global population is supplied largely or entirely by karst water
25%
Cenote
A circular water filled shaft in subdued karstic plains; developed through cave collapse or upward solution along fractures
Karren
A term used to describe all superficial small features typically found on limestone pavement Are typically small solution pits, grooves, and runnels
What do Speolothems indicate?
Amount of growth is an indicator of how much ground water percolates into the cave Little growth: drought Rapid growth: heavy precipitation
Speolothems
Cave depositions of precipitation of cave calcite and other materials
Collapse Sinkholes
Collapse of bedrock into an underlying solution cavity. Form when the top of the sinkhole collapses because drop in groundwater levels
Groundwater
Comes from precipitation. Water filters down through the vadose zone to reach the phreatic zone. The rate of infiltration is partially a function of soil and rock type and time
Helicites
Demonstrate the power of capillary action
Phreatic Caves
Develop completely in the pheratic zone Evidence: in the passageways - equal erosion of ceilings, walls, and floors
Staligmite
Develop where drops fall to the floor
Poljes
Elongated basins with flat floors and steep rock walls; floors are often covered by alluvium Flood during wet periods These are the largest karstic depressions
Pavement
Extensive horizontal bare rock surface
Exsurgent Spring
Fed mainly by the diffuse flow of water seeping down through the rocks
Intermediate Zone
Flow-gravitational or under pressure
Cockpit Karst
Form in wetter regions Sinkholes may coalesce Upside down egg carton
Gorges
Form when large volume streams flow over rocks susceptible to chemical weathering but not mass wasting. Result is deep valleys with very steep sides well past the angle of repose
Stalactite
Formed by drips on ceilings, from water percolating through joints or other fractures
Suffosion
How sinkholes form Occur when unconsolidated overburden sediments infill preexisting cavities below them
Caves - frequently associated with faulting
Hydraulic gradient creates the overall orientation but individual cave segments typically follow bedding planes, joints or faults
Where do caves develop?
In the unsaturated vadose Zone
Pressure Grouting
Injection of a low slump grout, which mainly consist of cement, sand, fly ash, into soils at/below limestone layer
Tower Karst
Isolated carbonate hills surrounded by flat plains Produced by over steepening of soluble rocks If there is alluvium or other permeable rocks in the tower there are often springs at the base of the tower
Mammoth Caves
Large cave developing at contact between limestone and impermeable rock (fairly thin and essentially flat laying rock)
Features of a Sinkhole
Limestone, carbonate rock Oval or circular shaped with sloping vertical sides Occur as an isolated entity or in groups
Allocthonous Sediments
Materials brought into the cave - mud, sand, gravel
Autochtonous Sediments
Materials created in the cave - calcareous products of solution and redeposition of material
Keyhole Passage
Modification by flow in the vadose as water level drops, the more circular portion formed by water flow in the pheratic zone
Vadose Caves
Mostly develop above the water table. Drainage is free flowing under gravity; cave passages have air above any water surface Exist in the upper part of karst aquifer Eventually drainage goes into pheratic zone or out to the surface
Calcite Straws
Precipitation of circular rings of calcite
Flowstone
Produced by water running or flowing down the walls and over the floors of caves (also known as cave bacon)
Karst Springs
Receive drainage from all sinkholes and sinking streams within its groundwater basin. Conduits carrying water from each point where water sinks join together underground, forming successively larger passages with ever-increasing flow, which eventually discharges at a spring. LARGE DISCHARGE
Disappearing Streams; Sinks
Rivers can disappear and reappear in karst terrain Places where the stream disappear are called sinks or vents
Signs that you may be living with Karst
Slumping or sagging - tilting of vertical objects Structural failure: cracks in mortar/pavement, windows/trim developing spaces, floors become uneven Rainfall pooling Vegetative stress - lowering of the water table Exposure of tree roots and rocks
Solution sinkholes
Solution acting from the surface downwards on fracture or joints. Form when the bedrock continues to be dissolved
Caves - frequently associated with jointing
Tend to be high, narrow and winding
Solution
The process by which karst forms in carbonate rocks (limestone)
Dissociation
The process by which karst forms in evaporites. It is the separation of cations and anions and their dispersal in water
Vadose Shaft
Water flowing down vertical or steeply dipping fractures
Hazards involved with living near karst
Water resource contamination due to the fact that karst is porous Can damage property
Vadose Zone
Zone of aeration that is unsaturated. It varies in thickness; function of sediment. The hydrostatic pressure is less than the atmospheric pressure. Gravity is pulling the water downward
Phreatic Zone
Zone of saturation. The hydrostatic pressure is greater than the atmospheric pressure; water flows easily
Resurgent Spring
fed by conduit flow where surface rivers disappear underground; react to rainfall faster with much greater maximum flows
Downward Sinkholes
lowering of the water table, removes buoyant supports and increase weight of roof
Polygonal Karst
star-shapped depression separated by residual cone-shaped or pinnacle shapped divides Common in Jamaica.... May form as the result of higher rainfall intensity in tropical regions which cause rapid runoff, surface flow, runnel and gully development