Download karst topography

BY
Faizan Saleem
BS-APPLIED GEOLOGY
Objectives of this Presentation
 Chemical Weathering
 Dissolution
 Karst Topography
 Karst Features/Landforms
 Groundwater
 Factors in development of Karst Landforms
Weathering
 The Physical or Chemical break down of rocks is called
Weathering.
 It has two types:
(1) Mechanical Weathering
(2) Chemical Weathering
Here I discuss Chemical Weathering.
Chemical Weathering
 The process in which rocks break down into sediments and
their chemical composition also change.
 It has different types but according to Presentation Topic
(Karst Topography) the most important is:
Dissolution:
In this process CO2 from atmosphere react with water to form
Acid
(H2CO3),that
reacts
with
Carbonate
rocks
Limestone,Dolomite etc. to dissolve them and forms different
features/landforms which termed as Karst Landforms.
KARST TOPOGRAPHY
Karst topography is named for the Kras plateau in
Slovenia. Karst is derived from the German word Kras
meaning "barren land."
Karst Topography is a landscape that has been formed by
dissolution of carbonate rocks such as limestone or
dolomite, or evaporates such as rock salt or gypsum.
Chemistry of Karst Topography
When CO2 reacts with water:
(i) CO2 + H2O -------> H2CO3
(ii) H2CO3 + CaCO3 --------> Ca + 2HCO3
Karst Landforms/Features
There are following Karst Landforms:
 Sinkholes/Dolines
 Caverns
 Stalactites, Stalagmites and Column
 Disappearing Streams
 Karst Springs
 Limestone Pavements
Sinkholes/Dolines
 A doline, sink or sinkhole is a low area or hole in the
ground that is formed especially when soil and rocks are
removed by flowing water.
 It can be cylindrical, conical, bowl- or dish-shaped
 There are two different mechanisms for the forming of
dolines/Sinkholes:
1) Collapse
2) Solution
Collapse:
Collapse sinkholes form when surface materials suddenly
sink into a subsurface cavity or cave. The cavities form
slowly over time, as groundwater moves along fractures
in soluble bedrock
and enlarges them through
dissolution
Solution:
The corrosive solution of limestone by rainwater is very
high in the area of crack, allowing the water to run into
the rock. This normally forms the bowlshaped type of
dolines.
Sinkholes by Solution
Sinkhole in California
Sinkhole in Russia
Caverns
 Caverns are formed by erosion caused by rain. The water
would seep down into the ground, dissolving rock
material, creating the caverns.
 These are interconnected in Limestone.
i.
ii.
If Caves linked horizontaly,then these called Galleries.
If linked vertically then these called,Shafts.
How a Cave Forms
Cave in Slovenia
Stalactites , Stalagmites and
Column
 When underground in a cave, you may find cone-like
limestone structures on the ceiling and the floor. On the
ceiling are Stalactites. (They hold on tite.).
 On the floor are Stalagmites.
 Where they meet, the combined structure is called a
Column.
Disappearing Streams
 A disappearing stream is the term used to describe a
stream or a river, which flows into a sinkhole or a crack.
Karst Springs
 Springs. A spring is a natural flow of groundwater from a
rock opening that results when the water table intersects
a sloping land surface.
 Springs can be seasonal—for example, during the wet
season the saturated zone is closer to the surface because
of increased rainfall, often resulting in more springs.
Limestone Pavements
 A horizontal or gently sloping expanse of bare limestone,
consisting of large blocks separated by deep eroded fissures.
 They formed by dissolution of Limestone by rainwater on
earth surface.Limestone is exposed on ground.
 There are following features of Limestone Pavements:
Clints
ii. Grikes
iii. Karren
i.
Clints:
A section of a limestone pavement separated from
adjacent sections by solution fissures.
Grikes:
A solution fissure, a vertical crack about 0.5 m wide formed
by the dissolving of limestone by water, that divides
an exposed limestone surface into sections or clints.
Karren/Lapies:
Small hollow that forms on the surface of a limestone clint
Groundwater Occurence
Groundwater occurs in 2 zones in subsurface:
i. Zone of Saturation
ii. Zone of Aeration
Zone of Saturation:


It is that zone of rocks where all rocks are saturated
with groundwater.
All the openings and pores are fully filled with water in
this zone.
Water Table:
“The top surface of Zone of Saturation is called as Water
Table.”
Perched Water-table:
“A perched water table is an accumulation of groundwater
located above a water table in an unsaturated zone.”
Zone of Aeration:
 The zone which is above the Water Table and below the
surface of the earth.
 The openings and pores in this zone are partially filled
with water.
 In this zone, Chemical action on rocks takes place.
Groundwater Zones
Aquifers:
 “A body of permeable rock which can contain or transmit
groundwater.”
 Aquitards. Impermeable formations such as shale, clay, or
unfractured igneous rocks that retard water flow are
called aquitards or aquicludes.
Aquifer
Factors in Development of Karst
Landforms
(1) Warm Temperatures:
 High temperature: Increases biochemical activity so that more
CO2 and organic acids are formed
 Low temperature:
a. Cold water has a higher potential of becoming more acid.
b. In cold regions dissolution is actually less because there is
less CO2 available to dissolve in water due to low
biochemical activity.
(2) Pressure:
 Water under pressure can dissolve more CO2 and
therefore hold more CaCO3 in solution.

Release of pressure will result in deposition of
CaCO3from water previously under hydraulic pressure
(e.g. travertine).
 Turbulence may also result in deposition (e.g.tufa
deposits in rivers)
(3) Rocks Properties:
There are two properties of rocks that affects development of
Karst Landscapes.
Porosity:
i. The Percentage of pore spaces in a given volume of rocks.
ii. Coarse and rounded sediments has more Porous than fine
and angular sediments.
iii. Igneous and Metamorphic rocks are less porous than
Sedimentary rocks.
Permeability:
i. It is the ability of a rock to transmit water through it.
ii. A rock may be porous without being permeable but can not
be permeable without having pores.
(4) High rainfall:
More water more solution,less precipitation less water.
(5) Joints:
 If small joints present between rocks then less water
enters in them, causes less dissolving.
 If joints are large then more water seeps in them and
more limestone dissolve.