Goh Cheng Leong Chapter 4: Weathering, Mass Movement and Groundwater YouTube Lecture Handouts

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Watch video lecture on YouTube: Goh Cheng Leong Chapter 4: Weathering, Mass Movement & Groundwater Goh Cheng Leong Chapter 4: Weathering, Mass Movement & Groundwater
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Earth crust undergoes changes:

  • Internal forces – orogenesis (folding and faulting)

  • External forces – interaction of constructive an destructive forces (lowering and levelling out) – denudation

Weathering – disintegration

Erosion – wearing away by moving agents

Transportation – removal of eroded particles

Deposition – dumping and accumulation to form new rocks

Watch video lecture on YouTube: Weathering & Erosion - 3 Types and 6 Agents Weathering & Erosion - 3 Types and 6 Agents
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These depends on:

  • Relief

  • Rock

  • Climate

  • Human interference

Weathering

Chemical Weathering

Slow process with gradual decomposition of rocks

Air and water contain chemical elements that accentuate the process

Malaysia – Granite (quartz, feldspar and mica) which is pitted and rough; feldspar is quickly weathered than quartz – quartz loosen and form sandy residue

Regolith- mineral remains of decomposed rocks with organic residue (has corestone which is most resistant)

In presence of soil cover – chemical weathering enhances (soil absorbs rainwater and is in contact with moisture)

Solution

  • Minerals are dissolved by water – contains to make weak acid

  • Common in limestone region – calcium carbonate

  • Solution is affected by composition and structure

  • Tropical nations – heavy rain and warm climate promote rapid chemical reactions (warm wet promotes while dry weather inhibits)

Oxidation

  • Reaction of oxygen in air and water with minerals in rock

  • Oxidation of iron and rusting (crumbles and erodes)

Decomposition by organic acids

  • Bacteria that thrive on decaying plants and animals

  • Produce acids that speed up the process

  • Absorb chemical elements from rocks and produce organic acids

Physical Weathering

Repeated temperature change

  • Desert area – constant heat and sudden drop of temperature in night

  • Rock split or breaks into rectangular blocks

  • Shales and slates split into platy fragments

  • In crystalline rocks – quartz, mica, feldspar expand and contract

  • Maximum stress and pressure near rock surface and where sharp angles are there in the rocks

  • Onion peeling – exfoliation (peeled in layers)

Repeated wetting and drying

  • Tropical regions of Malaysia – short downpour saturate the rocks and hot sun dries it again

  • Occurs in coastal area where rocks are dried by sun and wind between tides

Frost action

  • Seen in temperate areas

  • Temperature drops in night and in winter – water expands by 1/10th its volume and exerts pressure

  • It deepens the cracks

  • On mountains it creates pinnacles and angular outlines

  • This is known as frost shattered peaks

  • Angular fragments fall to foot of slope and accumulate as screes

Biotic factors

  • Loosened by chemical or mechanical weathering

  • Roots penetrate along the joints

Mass Movement

Watch video lecture on YouTube: Mass Wasting and Landslides - Types, Components, Causes and Prone Areas Mass Wasting and Landslides - Types, Components, Causes and Prone Areas
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Movement of weathered material down the slope due to gravitational forces

Movement can be slow or sudden, depend on slope gradient, weight of debris and lubricating moisture supplied by rainwater

Soil creep

  • Slow and gradual

  • More or less continuous movement of downhill slopes

  • Not noticeable if slope is gentle and soil is covered with grasses

  • Common in damp soils where water act as lubricant

  • Common in areas of continuous grazing by animals to create vibrations

Soil flow

  • Soil is saturated with water

  • Soil acts like a liquid

  • In arid areas it becomes saturated with rainwater after a storm and flow as semi-liquid mass

  • In temperate and tundra – it occurs when frozen surface thaws in spring

  • In peat soils – peat absorbs more moisture, if saturation point is reached soil may flow downslope – known as “bog-bursts” in Ireland

Landslides (Slumping and Sliding)

  • Steep slopes of mountains and cliffs

  • Caused by steep undercut by river or sea, so that it falls by gravity

  • Soil can be loosened by earthquake, volcano, man-made reasons, lubrication action of rainwater & water may collect in joints

  • Slumping: permeable debris or rocks lie over impermeable strata as clay

Image of Outline the process of slumping

Image of Outline the Process of Slumping

Image of Outline the process of slumping

  • Water may collect at base of regolith as it sinks into weathered material

  • Landslide possibility is enhanced by clearing the vegetation for agriculture and housing

  • Cameron Highlands – steep slopes are cleared has higher evidence of minor slumps

Groundwater

Watch video lecture on YouTube: Groundwater - Hydrogeology, 3 Zones, Process & Factors, Aquifers, Aquiclude, Aquitard Groundwater - Hydrogeology, 3 Zones, Process & Factors, Aquifers, Aquiclude, Aquitard
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  • Hydrological cycle – process of circulation of water b/w land, sea and atmosphere

    • Evaporation

    • Transpiration

    • Run-off

  • Plays major role in weathering and mass movement

  • Means of natural water storage

  • Water re-enters hydrological cycle by springs

  • Dry climate – precipitation is evaporated quickly and little moisture percolate into ground

  • In humid areas – most water runs off and sinks into ground

  • Porous Rocks – sandstone – many pore spaces exists (water is absorbed and stored)

  • Permeable or pervious rocks - allow water to pass through them

  • Impermeable – Clay is highly porous as made of many fine particles but spaces are very small and particle cannot move

  • Granite – nonporous but pervious as individual crystals absorb little or no water – but rocks can have joints through which water can pass

Water Table

  • Water moves down by gravity and reach impermeable layer through which it cannot pass

  • If no outlet is there, water accumulates above impermeable rocks and saturates – water gets stored as aquifers

  • Surface is known as water table and depth varies with seasons, relief and types of rocks

  • Water table is far below surface in hill tops but close to surface in valleys and flat low lying areas causing water logging

  • It rises in rain season and drops in dry seasons

Spring and Wells

Spring

  • Groundwater stored in rock reaches the point where the water table reaches the surface

  • Water may gush out as fountain

  • Tilted strata: alternate permeable and impermeable rocks and water emerges at base of permeable layers

  • Well-jointed rocks: water percolates down till it reaches joints and emerges at surface

  • Impermeable dyke or sill: causes water table to reach surface and water issues as spring

  • Permeable rock between impermeable rocks – water issues at foot of scarp as scarp foot & near foot of dip slope as dip-slope spring

  • Karst area – river appears, disappears and reemerges – vauclusian spring and is referred as resurgence

  • Hot spring, mineral spring and geysers in next chapter

Wells

  • Springs are natural but wells are man-made

  • Hole is bored until it reaches water table of permanent depth with continuous flow of water

  • Water is raised by hand or mechanical pumping

  • Commonly seen in arid areas with little surface water

  • Artesian well – nature of formation

  • Rock layer is down folded as basin – permanent strata is sandwiched between impermeable layers like clay

  • Water will fall down by gravity until it reaches lowest part of basin

  • Aquifer is saturated to the brim of the basin

  • Water is trapped in the aquifer under pressure & when well is bored, pressure of water downwards forces the water up the bore hole to gush as fountain

  • After sometime pressure decreases and pumping is not required

  • Depth varies

  • Commonly seen in Australia & Sahara desert areas

  • This water is unsuitable for agriculture as it is hot and contains lots of mineral salts

  • Wells deplete groundwater as water is extracted faster than natural conditions and much faster than it can be replenished by rainfall