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

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• 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

• 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)

• 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

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

-Manishika