Chapter_15 Limestone Environmet
Transcript of Chapter_15 Limestone Environmet
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Chapter 15
Limestone
Environment
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Limestone landscape
• A limestone region characterised by sinkholes and
caves is known as karst
• It is formed by the chemical weathering (carbonation
and solution) of limestone rocks
Formation of karst
• When rainwater reacts with carbon dioxide in the air or
in the soil, it forms carbonic acid
• The acid changes the calcium carbonate in limestone tocalcium bicarbonate which dissolves in water
• This rocess results in the formation of karst features
on the surface and beneath it
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Importance of understanding karst systems
• !arst landscaes make u about "#$ of the %arth&s
surface
• They are most abundant in troical humid regions but
also occur in temerate, troical, aline and olar
environments
• A 'uarter of the world&s oulation deend on water
sulied from karst areas
• owever, karst systems are vulnerable to groundwater
ollution due to the relatively raid water flow and the
lack of a natural filtration system
• ocal drinking water sulies risk being contaminated
as a result
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Limestone pavements
• *lat areas of exosed limestone
• +esemble artificial avements
• omrise large rectangular blocks called clints
searated by long grooves known as grikes
• A result of chemical weathering along the -oints andcracks in the limestone rocks
• The grikes will deeen
and widen over time
Chapter 15: Limestone Environment
A limestone pavement in Malham Cove,
England
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Sinkholes
• .eressions in the land surface
• aused by the dissolving of underlying limestone and
the collase of surface material
• A river that flows over a limestone area may disaear
down a sinkhole
• hemical weathering couled with erosion by the river
may enlarge the grikes on the surface until they become
holes, causing the river to disaear into underground
caverns and channels
• The art of the original channel downstream where the
river formerly flowed is called a /dry valley&
• The river returns to the surface at the /resurgence oint&
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Chapter 15: Limestone Environment
Sinkholes
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Dry valleys
• 0tee1sided valleys that no longer have water flowing
over the surface
• .uring the last ice age, limestone was fro2en to great
deths
• As the climate warmed, melting ice formed rivers that
carved out valleys over the still1fro2en rocks
• When the rocks thawed, the water infiltrated down
through the rocks and the valleys were left with no
surface water, resulting in dry valleys
• 3nderground caves may form below dry valleys
• The caves may collase to form a gorge
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Chapter 15: Limestone Environment
• A small deression
formed when one cave
collases is called adoline
• When several dolines
coalesce, they form a
ol-e or uvala
Sinkhole Plain, a limestone
environment near Mammoth
Cave, USA
ater
ta!le
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Stalactites and stalagmites
• Water that dris from the roof of a cave contains
calcium carbonate
• When the water dros fall, they leave behind some
calcium carbonate
• The water dros also deosit calcium carbonate on the
floor of the cave
• These deosits accumulate to form stalactites (hanging
from the roof) and stalagmites (on the ground)
• When water flows down the walls and over the floor of
the cave, flowstone or rimstone deosits are formed
• When water dris over the edges of ledges, thin sheets
of deosits called draeries are formed
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Chapter 15: Limestone Environment
Stalactites and stalagmites in a cave
Stalagmite
Stalactite
"nderground
pool
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#rotecting karst resources in the Cari!!ean
• The aribbean has one of the world&s remier karst
landscaes (which make u more than half of the total
land area of the region)
• About 4#$ of the karst is in the 5reater Antilles
• 6ther significant areas are in the 7ahamas, Anguilla,
Antigua, the ayman Islands, the 8irgin Islands,
5uadeloue, 7arbados, Trinidad and Tobago, and the
9etherlands Antilles
• :ost countries have adoted conservative strategies in
the establishment of arks, reserves and sanctuariesencomassing karst landscaes
• +egionally, there are ";" rotected karst areas,
covering "<=>$ of the total karst
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Chapter 15: Limestone Environment
Economic value of karst
1. Agriculture
• 0ome karst regions have rich and highly roductive soils
• The caves may be used for secialised agricultural activities
such as fish breeding, mushroom growing and cheese
roduction
• In 0outheast Asia, limestone caves are an imortant sourceof bird&s nest
2. Industry
• imestone is an imortant raw material for steel1making and
cement
• It is also used to reduce some forms of industrial ollution,
e=g= by removing sulhur dioxide from gases
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Chapter 15: Limestone Environment
3. Tourism
• Annually, about ;#
million eoleworldwide visit
limestone caves
• The 5reen 5rotto
aves in ?amaica,
arrison&s ave in7arbados and
5asaree aves in
Trinidad are tourist
attractions
• Tourism is animortant source
of income for the
residents in karst
areas
$arrison%s Cave
&asparee Caves
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Scientific value of karst• !arsts are a key source of information on landform evolution and
climate change• The caves contain imortant archaeological and alaeontological
material
• !arsts host various endangered lant and animal secies, both
underground and on the surface
'ecreational value of karst• !arsts offer oortunities for caving, which has become a oular
recreational activity
• This contributes to tourism
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(hreats to karst systems
• .rawing of water within karst areas disturbs the
hydrological system
• The water level and the water 'uality are threatened
• :oisture within the cave microclimate is affected
• The lant and animal secies in the caves aresubse'uently affected
• @uarrying for recious minerals such as bauxite
destroys the caves
• .uming of sewage and domestic and industrial wastecan lead to groundwater ollution as there is little
natural filtration in karst regions
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Case study: (he )amaican karst landscape *
Cockpit Country
• :ostly located in Trelawny, but sreads through the
neighbouring arishes of 0t %li2abeth and 0t ?ames
• haracterised by a regular series of round1toed
conical hills and its
Chapter 15: Limestone Environment
The landscape of Cockpit
Country
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*ormation
• ockit ountry is a massive limestone lateau with an
elevation of about ##m above sea level
• According to one theory, its characteristic toograhy is
the result of heavy troical rain washing through the
fissured lateau over millions of years
• The water dissolved and eroded the fissures andwashed the debris through the sinkholes into the sea
• Another theory ostulates that water moves slowly at the
to of the hills with little erosion
• As the water flowed downhill, it icked u momentumand gathered debris, resulting in a more ronounced
scouring action
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*eatures of a karst landscae
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Identifying karst features on a topographical map• 3ndulating landscae as indicated by the irregular
contour attern• .ry valleys• .eressions B as indicated by
short hash marks inside circles• .isaearing streams
• 0rings at the foot of steeescarments and lace namesthat begin with /sring& such as/0ringvale&=
• .ee gorges
• *eatures and symbols that reresent 'uarries andcement1making, since limestone is an imortantingredient for cement roduction
• ittle or no surface drainage
Chapter 15: Limestone Environment