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Geog375Gmphlgy > Karst and Karst Terranes > Flashcards

Karst and Karst Terranes Flashcards

1
Q

The word Karst stems from?

A
  • German form of the Yugoslavian term “Kras”

- Meaning ‘bare stony ground’

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2
Q

In modern geomorphology, Karst refers to what?

A
  • Landscape formed by dissolution of the underlying bedrock

- Characterized by distinctive landforms that don’t typically occur in any other circumstance

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3
Q

The term ‘pseudo-karst’ refers to?

A
  • Karst-like development in non-carbonate lithology
  • Exhibits characteristics similar to karst landscapes
  • But lack dissolution as a primary means of landscape formation
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4
Q

Major known global karst regions

A
  • Mexico, Mid US,
    Canadian Rockies, SE Asia, Parts of Australia, Spain, Italy, etc.
  • Equatorial areas from high temps and are areas of both limestone formation and dissolution
  • Exception is SA, not much there
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5
Q

BC carbonates

A
  • Rockies

- Some on Van Isle and Haida Gwaii

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6
Q

Factors that affect Karst development

A
  • Solubility of limestone (percent calcite)
  • Climate (temp and moisture)
  • Structure of limestone (joints, fractures, porosity)
  • Mineralogy/Lithological content (percent classics, percent spar vs. micrite vs. skeletal)
  • Vegetation/non-carbonate geology (acidity/pH of groundwater from humic acids)
  • Atmospheric CO2 (affects solubility of carbonates)
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7
Q

What is the main thing karst topography requires?

A
  • Limestone!
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8
Q

Overview of karst formation

A
  • CO2 in air and soil combine w/ water to form carbonic acid, dissolves limestone, especially along fractures
  • Subsurface dissolution/erosion forms water-filled caves
  • Water table lowering drains caves, carbonates precipitate
  • Cave roofs collapse, cause sinkholes/ other landforms
  • Over time, erosion and dissolution lead to remnant rock towers (Asia)
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9
Q

Carbonate geochemistry

A

Rainfall is acidic (pH 5.6) b/c atmospheric CO2 and water produce carbonic acid

  • Carbonic acid dissociates into hydrogen and bicarbonate ions
  • Equilibrium equation
  • Carbonic acid dissolves limestone to produce calcium and bicarbonate ions
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10
Q

Other controls on groundwater acidity and carbonate geochemistry

A
  • Soil water gets highly enriched in CO2 from respiration of plant roots and microbe decomposition of organic matter
  • Cold water can dissolve/hold more CO2 than warm
  • More CO2 is dissolved in water as the partial pressure of the air increases (e.g. in soil pore space,), increases CO2 in oceans
  • More limestone increases bicarbonate
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11
Q

What temperature of water can hold more CO2?

A

Cold water

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12
Q

Dissolution of carbonates

A
  • Process by which rock is dissolved in water (assisted by carbonic acid)
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13
Q

What does increased CO2 in water do?

A
  • Decreases pH

- Increases rate of dissolution

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14
Q

What does increased biological activity do?

A
  • Enhances dissolution b/c it generates CO2

- CO2 generated by respiration of plant roots and decomposition of organic matter by microbes

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15
Q

What is the dominant ion in runoff?

A
  • Bicarbonate, HCO3-

- Due to carbonate dissolution

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16
Q

Precipitation of carbonate is what?

A
  • Opposite to dissolution

- Occurs when CO2 evaporates from water, e.g. in caves

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17
Q

Dissolution of Dolomite

A
  • CaMg(CO3)2 breaks down to Ca2+, Mg2+, and 2C032-

- Rate of dissolution is higher if carbonic acid is involved, just like limestone

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18
Q

What are examples of other minerals that can dissolve in water?

A
  • Dolomite, chalk, gypsum

- Break down into constituent ions

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19
Q

Karst landscapes are shaped through…?

A
  • Dissolution of soluble bedrock
  • Commonly limestone or dolomite
  • Sinkholes develop and cavities are dissolved below ground
  • Surface water may become limited
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20
Q

3 Cycles of karst terrain erosion

A
  • Youthful (Normal surface drainage, to dry valley’s, swallow holes, underground streams)
  • Mature (Roof collapse, surface hollows)
  • Old age (Hums, and remnant rock towers, worn down to impermeable basement in areas)
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21
Q

Landforms that form above the water table

A
  • Collapse sinkholes, karren, grikes, abandoned caves, speleothems
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22
Q

Grikes

A
  • Kluftkarren
  • Solution enhanced vertical fractures
  • Divide surface into distinct pieces referred to as Clints
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23
Q

Speleothems

A
  • Cave deposits
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24
Q

Landforms that form below the water table

A
  • interconnected caves, tunnels, other cavities, solution sink-holes, springs
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25
Q

Karrens

A
  • Large tracts of limestone karst terranes that are devoid of unconsolidated material
  • Often solution enhanced vertical fracture/ joint sets
  • Can be filled w/ debris from dissolution or devoid of residuum
  • Not good for growing, sometimes loess may provide nutrients for plants to grow in cracks
  • Openings known as grikes, kluftkarren or solution grooves
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26
Q

Ireland

A
  • Karren, grikes and clints
  • Limestone pavements, rugged and bare w/ flat areas of rock
  • The Burren in county Clare formed during carboniferous (355-290Ma)
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27
Q

Formation of grikes and clints

A
  • Water drainage and flow concentrates along joints, fractures and structural weaknesses
  • Dissolution preferentially along the cracks enlarges them
  • Joints/ fractures may connect at subsurface and underground drainage systems develop
28
Q

Karst collapse landforms

A
  • Sinkholes, Dolines, Cenotes, Cockpits
  • Often funnel shaped
  • From as material above cavity becomes too thin to support weight
  • Sometimes filled w/ colluvium from edges or overlying strata
  • Can form circular lakes
  • Entrances to karst caves are often old sinkholes
29
Q

What are the 2 categories of sinkholes?

A
  • Collapse, usually form when water level drops

- Solution, form due to dissolution at surface

30
Q

Cenotes

A
  • Sinkholes (Yucatan, Florida)
  • Flood and dissolve during high SL interglacials
  • Collapse during low SL glacials
31
Q

Cockpit

A
  • Sinkhole surrounded by hemispheroidal residual hills

- Ex. Arecibo Radio Astronomy observatory, Puerto Rico

32
Q

Compound sinkholes

A
  • Uvalas
  • Several sinkholes coalesce, form larger structure (up to km scale)
  • Sometimes floored w/ alluvium from subterranean streams, called karst gulf or polje
  • Can develop quickly to >100m depth, can cause destruction/ death
33
Q

Polje

A
  • Large (25km^2) elongated basin in karst terrane
  • Flat floor, steep walls, structurally controlled
  • Formed by coalescence of many sinkholes (Uvulas)
  • Often w/ disappearing streams
34
Q

Drainage in European karst region

A
  • Polje basin

- Flooded and backed up into overflow channels

35
Q

Drainage characteristics of Karst terrain

A
  • Chaotic or deranged pattern
  • Few, if any, through flowing streams
  • Blind valleys, lost rivers, tributaries and other surface streams
  • Streams disappear into ‘swallow hole’ (called ponor, swallet or a sink)
  • Often reappear as karst spring or gw rise
  • Surface drainage replaced by underground
36
Q

Australian karst terrain

A
  • Karren plains w/ blind valleys and numerous sinkholes
37
Q

Swallow holes

A
  • AKA Ponor, swallet, sluggas
  • River reaches permeable rock, Disappears down grikes
  • Grikes enlarge through dissolution
  • Forms swallow hole
38
Q

Dry valley

A
  • Remains of river valley downstream from sinkhole

- If river reappears at surface, its called ‘River of Resurgence’

39
Q

River of Resurgence

A
  • Reappearance of a stream downstream of a dry valley/ sinkhole
40
Q

Mitchell Plain and Chester Escarpment

A
  • Karst terrain w/ sinkholes, hummocky

- Equivalent in Kentucky

41
Q

Karst surface water features

A
  • Karst regions noted for ‘lack of well-established surface drainage’
  • Surface streams tend not to flow very far
  • Become ‘Disappearing streams’
  • Can reappear at surface as springs, usually from a cave
42
Q

Underground landforms, cave formation

A
  • Surface water enters through swallow holes, grikes, etc.
  • Passages enlarge via carbonation and dissolution, leads to large caverns
  • Water erodes rock by abrasion and hydraulic action
  • Caves develop at or below zone of saturation
  • Water table lowers/ tectonic uplift drains cave
  • Cave may continue to enlarge via rockfall
43
Q

Cave development

A
  • Dissolution along joints/ bedding planes
  • Cave erosion and expansion
  • Caves surface at artesian or gravity springs
  • Drainage and abandonment, inactive
44
Q

2 examples of large N. American caves

A
  • Mammoth cave, KY

- Hall of Giants, Carlsbad Caverns, NM

45
Q

Speleothems

A
  • Cave deposits

- Soda straws, stalactites/ stalagmites, drapes, columns, flow stones, pool spar and shelfstones

46
Q

Dripstones, speleothem

A
  • Water drops containing dissolved limestone seep through cracks and fissures in cave roof
  • Water enriched in CO2 from soil
  • When exposed to cave air, water loses CO2 and deposits calcite
47
Q

Stalactite

A
  • Common interior cave formation
  • C = ceiling, ceiling icicles
  • Water dripping from cave top loses CO2 and deposits calcite, initially as delicate soda straws
  • Over time deposition forms large hanging features
48
Q

Stalagmite

A
  • Common interior cave formation
  • G = ground
  • Water droplets fall to cave floor and lose more CO2, deposit more calcite
  • Over time forms pillars growing upward from cave floor
  • Directly below stalactites, usually thicker
49
Q

Column

A
  • Cave formation

- When stalactite and stalagmite combine/ grow together

50
Q

Pool spar

A
  • Common interior cave formation
  • Crystallization of dissolved limestone in water
  • Looks like spiny starbursts
51
Q

Shelfstone

A
  • Common interior cave formation

- Develops when spar attach to side of cave pool

52
Q

Growth of stalctites

A
  • Soda straws initially hollow, allow for dissolved limestone to travel through tube
  • Dissolved solid can plug tube
  • Forces dissolved limestone to ‘back-up’ and flow on outside of straw
  • Thickens and becomes stalactite
53
Q

Largest free-hanging stalactite in N. hemisphere

A
  • Doolin Cave Ireland

- 7.3m long

54
Q

Soda Straws

A
  • Delicate, hollow tubes of calcite deposited and hanging from cave ceiling
  • Initiation of stalactite formation
55
Q

Pillars

A
  • Dripstone features
  • Stalactites and stalagmites grow toward each other
  • Eventually join in a pillar or column
56
Q

Curtains

A
  • Water drips from long cracks in cave roof

- Form continuous strips of calcite called curtains/ drapery

57
Q

Flowstones

A
  • Sheets of calcite deposited on the floor or walls by flowing water
58
Q

How are mini-terraces formed in caves?

A
  • Increased turbulence at flowstone margins release more CO2

- Encourages precipitation and development of terraces and calcite ‘waterfalls’

59
Q

Mature karst terrains

A
  • Humid regions (Puerto Rico, Jamaica, SE Asia/China)
  • Form towers, mounds, cockpit karst
  • Erosional remnants of thick sequences of limestone that have been greatly degraded
60
Q

Tower Karst

A
  • Formation due to combo of tectonic uplift and tropical erosion
  • China, Vietnam
61
Q

Importance of Karst

A
  • Covers approx. 10 percent of earth
  • 1/4 of world population depends on water from karst areas
  • Highly vulnerable to gw pollution, rapid rate of water flow into aquifer and lack of natural filtration
  • Tropical karst w/ extensive forest canopy hosts 100’s of unique plants and animals
  • Coastal wetlands rely on complex hydrological dynamics of karst to function properly
62
Q

Why is much of the 10 percent of karst earth surface w/o surface features?

A
  • Due to mantling of non-soluble strata
63
Q

Engineering solutions, Applied science building at UCSC example

A
  • Foundation cement kept disappearing into subsurface karst
  • Solution was structural pillars sunk deep into solid rock
  • Large cement pillars part of building foundation all the way to the top floor
64
Q

Van Isle cave examples

A
  • Horne Lake Caves Provincial Park
  • Sinkholes (funnel shaped) beside trails
  • Relict carbonate flowstones in Central Van Isle
65
Q

Stratification in caves…?

A
  • Records depositional history

- Paleoclimate reconstruction

66
Q

University of California, Santa Cruz

A
  • Built on dolines (sinkholes) formed by dissolution of bedrock or collapse of shallow caves
  • Home to Empire cave, formed by uplift of Santa Cruz mnts. and marine terraces, erosion of Cave Gulch
  • N-S orientation of passage way reflects other canyons and joints in quarries that are N-S
  • Much construction has to be modified to withstand dangers of landforms

Geog375Gmphlgy (9 decks)

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