Karst Geomorphology

Question 1

Importance of karst

Answer 1

• regions provide aquifers that are capable of providing large supplies of water (springs)
• > 25% of the worlds population either lives on or obtains its water from karst aquifers
• vital to understand its structure due to potential harzards:
• sinkhole, ground subsidence, groundwater contamination, variable water supple.

Question 2

Karst defined

Answer 2

a landscape formed mainly by rock being dissolved by surface or groundwater

• rock (typically limestone or salt)
• acidic surface water

Question 3

Karst distribution

Answer 3

• world distribution of surficial carbonate rocks
• formation (lakes/shallow marine systems)
• deposition (algae, shells, skeletal material, coral)
• precipitation of dissolved CaCO3
• chalk is very weak = no underground drainage

Question 4

what is karst

Answer 4

• terrain with distinctive geomorphology and hydrology arising form a combination of high rock solubility and well developed secondary porosity
• the key to karst is the unusual subsurface hydrology
• also pseudokarst, thermokarst and vulcanokarst

Question 5

Dissolution

Answer 5

process of rock dissolving when it comes into contact with water

Question 6

karst process

Answer 6

• dissolution
• rock/mineral is dissolved by surface or groundwater and transported in solution
• karst mostly occurs in humid regions where carbonate rock is present
• (karst does occur in every region; temperate, tropical, polar)

Question 7

Karst hydorlogy and geomorphology main processes

Answer 7

• solution
• precipitation
• subsidence
• collapse

Question 8

Karst processes

Answer 8

• true karst
• holokarst
• fluviokarst
• Glaciokarst
• thermokarst

Question 9

Karst drainage

Answer 9

• surface/near surface (epikarst)
• subsurface (endokarst)
• water table follows topography
• changes depth with changes in precipitation

Question 10

Vadose

Answer 10

aerated zone above water table

Question 11

Phreatic

Answer 11

saturated ground water zone

Question 12

solution in Karst

Answer 12

• carbonate rocks dissolve in weakly acidic water
• rainwater becomes acidic by dissolving CO2 = carbonic acid
• soil water are often acidic through the release of organic acids from rotting vegetation
• weathered minerals may also release acids

Question 13

carbonic acid formation

Answer 13

H2O + CO2 = H2CO3
- rainwater picks up carbon dioxide
H2CO3 = H+ + HCO3-
- carboic acid dissociates to produce hydrogen ions = acid (lowers pH)
- solution processes are more effective in warm/wet tropical climates

Question 14

solution of silicate rocks

Answer 14

• crystalline quartzite has low solubility (10%)
• dissolution of weak amorphous (non-crystalline) silica = increasing porosity = weakening (glass)
• less common, slower process

Question 15

cycle of development

Answer 15

• W.M.Davis, 1893
• Grund, 1903
• Cvijic, 1918

Question 16

factors effecting Karst processes

Answer 16

• solubility of bedrock, % calcite
• climate, temp and moisture
• structure of limestone, joints, fracture, porosity
• vegetation/non carbonate geology, pH of groundwater
• atmospheric CO2, affects solubility of carbonates

Question 17

surface Karst features (The Dinaric region, Slovenia)

Answer 17

• doline (depression in the land surface)
• ponor
• polje
• disappearing stream
• uvala
• limestone pavement
• fluting and grooving
• karst towers
• karst cones
• cave in karst tower
• resurgent stream with tufa bed
• cavern with stalagmites and stalactites
• subterranean channels

Question 18

Karren

Answer 18

• bare forms and covered forms
• small scale solution/sculpturing of ground surface or caves
• grikes, gutter, decantation flutings

Question 19

clinks and grikes

Answer 19

can develop into bogaz, corridors and streets (gorges)

- solution rates: 1mm/10-20 years

Question 20

covered karren

Answer 20

develop where you have full or partial soil cover

- acts like an acidic sponge

Question 21

limestone pavements

Answer 21

• juxtaposition of glacial and chemical weathering processes
• polygentic karst

Question 22

closed depressions formation process

Answer 22

• surface solution, concentration around a joint = positive feedback
• cave collapse: underground solution = collapse
• piping, joint widening
• subsidence, dissolution of salts

Question 23

Polje

Answer 23

• enclosed, flat bottomed, steep-sided depressions
• can extend over 100km
• based in bedrock or unconsolidated sediment
  3 types:
• border, (Dominated by allogenic sediment)
• Structural (geologically controlled graben)
• Base level, (controlled by water level)

Question 24

Polje can also be classified by hydrology characteristics related to their drainage pathways

Answer 24

• closed polje (subterranean drainage)
• upstream open polje (subterranean drainage)
• downstream open polje (surface and subsurface drainage)
• up and downstream open polje (surface and subsurface drainage)

Question 25

Polje uses

Answer 25

• characterised by seasonal flooding
• wetland areas favoured location for palaeolithic humans availablity resources)
• good source of palaeo-environmental and archaeological information

Question 26

Cone karst

Answer 26

• dominant in tropical environments
• dolines interact under intense chemical weathering = cone karst
• high run-off rates and thick soil = >soil CO2 = more acid

Question 27

fluvial karst

Answer 27

• karst landscapes dominated by subsurface water courses
• sinks through to the bed
• where water present, it is more effective agent than slope processes
• dry valleys, peak district Dorset

Question 28

Dry valley formation

Answer 28

• postglacial meltwater and permafrost thawing
• large amounts of fluvial action
• high volumes of water, unable to sink as ground saturated, channels blocked or flow rate too high
• depending on context, seasonal flooding and drying can take plate today

Question 29

cave formation

Answer 29

• kinetic: capillary flow = solution
• inheritance: pre-existing cavities are exploited
• hypergene: chemically enriched hydrothermal waters create cavities

Question 30

Speleogenesis (cave formation)

Answer 30

• chemical solution
• fluvial erosion
• tectonics
• microorganisms
• pressure
• atmospheric influences
• human

Question 31

cave types

Answer 31

classified based on their position relative to the water table:

• vadose
• deep phreatic
• water table or epiphreatic

Question 32

speleogen type

Answer 32

• potholes & current markings (erosion flowing water)
• rock pendants & scallops (solution features)
• larger = slower flow
• smaller = faster flow
• directional indicators

Question 33

speleothems

Answer 33

depositional features

• dripstone, straws
• flowstone (sheet-like, walls/floors)
• stalagmites/stalactites/columns

Question 34

formation Lechuguilla

Answer 34

• tectonic uplift = ground expansion/cracking
• known for oil reserves (release H2S)
• H2S combines with groundwater = sulphuric acid
• acid dissolved limestone = cave system
• unusually created bottom up rather than top down

Question 35

Karst landscapes are characterised by:

Answer 35

• Limited surface drainage
• Can form and be influenced by a multitude of contexts (Fluvial, Solution, Glacial, Thermokarst…)
• Extensive surficial and subterranean solution and erosion systems (evaporites, carbonates and occasionally silicate rocks)
• Range of scales of erosional and depositional features from microscopic karren to gorges and polje, straws and columns
• Karst landscapes are important as they act as sub-surface reservoirs of water
• They are also potentially hazardous if the subsurface systems are not well-mapped or understood.