Goh Cheng Leong Chapter 8: Limestone and Chalk Landform YouTube Lecture Handouts

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Goh Cheng Leong Chapter 8: Limestone and Chalk Landforms
  • Sedimentary rocks of organic origin from coral accumulation
  • Pure state – calcite or – soluble in rain water ( from air forms weak acid)
  • Along with magnesium called as dolomite
  • Also called karst topography – Karst district in Yugoslavia
  • Broken by precipitous slopes
  • Absence of surface drainage (most surface water is underground)
  • Streams on other rocks flow for short distance and then go underground & surface is dry
  • Water penetrates base of limestone and meets non-porous rocks it remerges on surface as spring or resurgence

Features

Limestone are well jointed

Rainwater finds the way through these cracks

Grikes (joints widened by chemical weathering)

Cracks enlarge into trenches as limestone pavements

Enlarged joints as grikes

Rectangular blocks as clints

Limestone Topography

Small depression on surface by rainwater – swallow holes

Where rainwater sinks into limestone at point of weakness – sink holes (example, Gaping Ghyll in Yorkshire) – these grow by solvent action

When water sunks into limestone it etches out caverns. When roof collapses limestone gorge as Cheddar Gorge is formed

Swallow holes coalesce to form large hole – Doline

Dolines merge to form – uvala (miles along with clayey soil)

Yugoslavia – large depressions of hundred square miles as polje due to faulting (during rainy season floor near water table become temporary lakes while drier areas are fertile & support large villages)

Topographic Watershed Divide

Streams descend through swallow holes into underground passage – with caves

Stalactites – from top or roofs and are downward pinnacles. Calcium carbonate is carried in solution, when water evaporates calcium carbonate solidifies

Stalagmites – from base – shorter, fatter and rounded

Stalactite and Stalagmite join to form pillars

Stalactite

Caves – Batu Caves (Kuala Lumpur) ; Mammoth Caves; Kentucky & Carlsbad Cave (New Mexico, USA) ; Postojna Caves (Yugoslavia)

Limestone Regions

  • Causses (S. France)
  • Pennines (Britain) – Yorkshire & Derbyshire
  • Kentucky (USA)
  • Yucatan Peninsula (Mexico)
  • Cockpit Country (Jamaica)

Human Activity in Karst Regions

  • Mainly barren
  • Thin soil
  • High porosity
  • Surface drainage is absent
  • Vegetative growth is difficult
  • Poor grass and short turf
  • In tropical areas – luxuriant growth with heavy rain throughout year
  • Scattered settlement
  • Sparse population
  • Lead occurs along with limestone
  • Used in building material for cement industry
  • West Malaysia – limestone outcrop of Kledang range & Main range is quarried for Pan-Malaysian and Tasek Cement Works

Chalk

  • Landform of chalk are different from limestone
  • Little or no surface drainage
  • Valleys once contained are now dry and called coombes
  • Low rounded hills in S & SE England
  • Called Downs in N. France
  • Covered with short turfs & woodland
  • Friable rocks – so swallow holes don՚t develop

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