Geography Chap 8 (Goh Cheng Leong + NCERT)

Chapter 8

Limestone and Chalk Landform

Limestone and Chalk:
--Sedimentary rocks + Organic origin
--Limestone forms =Marble = through sedimentation.
--Why Organic = accumulation of corals + shells in sea.
--Limestone =CaCO3
-- Dolomite= when Magnesium is also found with Limestone.
--Chalk= pure Limestone + Soft +white color.
--Weak ACID= Limestone is Soluble = in Water---When CO2 absorbed from atm =Forms weak acid.
--Karst region= A region with large stretch of limestone.
           >>Why Karst= a district “KARST” in Yugoslavia.

Features of Karst region:
--a bleak landscape ===occasionally broken precipitous(steep) slopes.
--Absence of surface drainage èmostly H2O flows under surface.
--Stream rising over other rocks-à pushes water to come to surface ---again goes underground limestone is encountered below.
--therefore Appearance=short distance water stream over surface.
--Going underground ?
         >water streams encounters “fissures / cracks /joints” on limestone surface ==further cuts its way to underground.
         > Swallow holes= when cracks enlarges.
         >Dolina= when many swallow holes merges.
         Uvala= Dolina merges to form Uvala.
         >Moves till it reaches a layer = non porous ===emerges as spring(on surface) .
--Limestone pavement= Cracks on surface enlarges to form= enlarged joints =Grikes; islolate block of lime stone= clints
         > these limestone pavement= formed below surface= come out @ weathering.
--Limestone George= when underground water channel collapse by surface weight.
--(Image : Limestone pavement↓):



(Image = Limestone  pavement diagram ↓):



--Limestone Cave:
à -- when subterranean stream(underground)------descends(goes down) through swallow holes === forms various structure in Caves(underground)
à-- structure= Stalactites + stalagmites + Pillars
à--Stalactites = A long pointed piece of rock hanging down from the roof of a cave.
à-- Stalagmites = A piece of rock pointing upwards from the floor of caves. ===formed by moisture dripping from Stalactites -----therefore lies just below.
à-- Pillars= when both Stalactites and stalagmites meets===forms pillar.
à===Example = Baratang island (Andaman island)
à -- (Image : Limestone cave↓):


--(Image: Limestone scenery ↓):

Human activity of Karst region
--(thin layer of soil) + (negligible surface water) = less vegetative growth.
--Poor grass ------sheep grazing usually.
--In tropical region = rainfall ↑ = more vegetation.
--Minerals= Lead( in veins of limestone) + Limestone(for cement).


Landform of Chalk
--AKA coombes.
--extremely dry à no surface water.
--No swallow holes and Underground caves= as Chalk are friable(easily broken).