BY Faizan Saleem BS-APPLIED GEOLOGY 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: Collapse 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 Russia Sinkhole in California

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. 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 Grikes Karren

Clints: Grikes: Karren/Lapies: 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: Zone of Saturation 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: Perched 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: Cold water has a higher potential of becoming more acid. 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: The Percentage of pore spaces in a given volume of rocks. Coarse and rounded sediments has more Porous than fine and angular sediments. Igneous and Metamorphic rocks are less porous than Sedimentary rocks. Permeability: It is the ability of a rock to transmit water through it. A rock may be porous without being permeable but can not be permeable without having pores.

(4) High rainfall: (5) Joints:  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.