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Geomorphology > Climate and Weathering > Flashcards

Climate and Weathering Flashcards

1
Q

Climate

A

Refers to characteristics atmospheric conditions over a long period of time
- years or decades

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2
Q

Weather

A

Refers to atmospheric conditions over short periods of time

- days or weeks

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3
Q

Influences on weathering

A
  • rock type and structure
  • topography
  • presence of organisms
  • age
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4
Q

Climate imposed effects of weathering

A
  • style
  • rate
  • volume
  • products
  • landscape
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5
Q

Weak leaching

A

smectite

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6
Q

Moderate leaching

A

kaolinite

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7
Q

Intense leaching

A

Gibbsite

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8
Q

Peltier (1950) scheme

A

Weathering rates related to temperature and rainfall

- intensity of chemical weathering

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9
Q

Weathering

A

breakdown of rick by;

  • mechanical
  • chemical
  • biological
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10
Q

Functions of weathering

A
  • give rock lower strength and greater permeability
  • produces landforms
  • releases minerals in solution
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11
Q

Mechanical weathering

A
  • Progressive breakdown
  • increases surface area of the rock for chemical weathering
  • fatigue, repetition of stress
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12
Q

Unloading (Mechanical)

A
  • Rocks exhumed from depth
  • Confining pressure is eased (erosion)
  • Allows mineral grain expansion (rockbursts)
  • Small surface-parallel fractures and joints
  • Exfoliation
  • May result in rock falls
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13
Q

Frost action (Mechanical)

A
  • physical disintegration (frost shattering
  • cold environments, cyclical freezing
    freezing = 9% increase in water volume
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14
Q

Heating and cooling (Mechanical)

A 
Isolation weathering 
• Rocks = low thermal conductivity
• Outer surface heats and expands quicker than rock core 
• Exfoliation
• Desert environments
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15
Q

Wetting and drying (Mechanical)

A 
• Often known as ‘Slaking’
• Water is attracted to
fractured minerals and
is aDsorbed
• In a crack this leads to swelling pressure
• Clay minerals encourage
water adsorption (e.g.
mudstones and shales)
• Cracks form on drying
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16
Q

Salt crystal growth (Mechanical)

A 
Haloclasty
• Evaporation of saline solution
• Salt crystal growth in rock
interstices = granular
disintegration 
• Important in coastal and
arid regions
• Evaporation of brine
where watertable close
to surface
17
Q

Action of plants and animals (Mechanical)

A
  • lichens and mosses grow on rocks
    • they wedge their tiny
      roots into spores and
      crevices
    • when the roots grow, the
      rock splits
  • trees and shrubs may grow in the cracks of boulders
18
Q

Chemical weathering

A 
• Caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts.
• Reactions occur particularly
when the water is slightly acidic
• Mainly from the action of
rainwater, oxygen, carbon
dioxide, and acids of plant decay
• Water vapor is present in
the air everywhere means that chemical weathering occurs everywhere
19
Q

Solution (Chemical)

A
  • mineral salts become dissolved in water
  • solubility of minerals depend on pH of the water
  • readily reversible = precipitate
  • important in limestone areas
20
Q

Hydration (Chemical)

A
  • transitional between chemical and mechanical
  • no change to chemical composition
  • absorption of water molecules into minerals lattices
  • stress from expansion of minerals
  • embeds water
21
Q

Oxidation and reduction (Chemical)

A
  • involves oxygen combing with a substance
  • oxygen dissolved in water is important oxidising agent
  • iron is highly susceptible
    element loses an electron to dissolved oxygen
  • Gives altered earth material a characteristic
    yellowish brown to red colour
  • Water table is boundary between oxidizing and
    reducing environments
22
Q

Carbonation (Chemical) - chain reaction

A
  • is the formation of carbonates
  • occurs when carbonic acid attacks minerals (calcareous rocks)
  • limestone reacts with carbonic acid to produce calcium hydrogen carbonate
  • calcium hydrogen carbonate = very soluble
23
Q

Hydrolysis (Chemical)

A
  • water splits into hydrogen irons and hydroxyl anions
  • these react with minerals
  • plagioclase to kaolinite produces soluble calcium carbonate
24
Q

Chelation (Chemical)

A
  • biochemical process
    • organisms produce organic substances, known as chelates
  • chelating agents are produced by alteration of humus in plant acids and excreted by lichens
  • decompose minerals and rocks from removal of metallic cations
  • forms soluble organic matter-metal complexes
25
Q

Reduction (Chemical)

A
  • Reverse process of oxidation
  • excess water present
  • oxygen is released by soil/rock
  • waterlogged conditions
  • ferric iron converted to ferrous forms
  • responsible for changing soil colour to grey, blue, green colours (gleying)
  • water table is high with impermeable layer
26
Q

Biological weathering

A

root penetration = bio-mechanical
- lichen growth or guano = thermal weathering
- coastal organisms bore and graze
- bacterial chemical secretions (alter minerals)
animal burrowing etc.

27
Q

Tor formation

A
  • Sedimentary cover rocks eroded quickly
  • Unloading to expansion and uplift of granite to horizontal joint formation
  • Granite weathering (kaolinisation) begins
  • Deep chemical weathering
  • Humid, wet climate
  • Acidic waters
28
Q

Weathering landforms

A 
Tors, Dartmoor (280Ma)
• Granite batholith cooled
• Composition – Quartz,
feldspar, biotite mica
• Cooling to initial vertical
cracks
• Faulting accentuated jointing
29
Q

Continued weathering of profile

A 
Block-fields
- mountain summits 
- periglacial activity
Talus Cones 
- accumulations of material loosened by weathering
Duricrust 
 - soluble materials precipitate
- more resistant layers formed (crust, nodules)
30
Q

Human activities (Biological)

A
  • quarries, dams, roads
  • climate change;
  • increased rainfall
  • warmer temps
  • chemical emissions
  • land clearance;
  • forestry and grazing land
31
Q

Final stage of tor formation

A 
• Quaternary glaciation
• Too cold for chemical
weathering
• Mechanical processes
take over (Freeze thaw/Solifluction in
permafrost)
• Removes weathered
debris
• Soil and boulders
32
Q

Soil?

A

Controversial!
- Geologists and Engineers see soils as = regolith
- Pedologists see soils as the portion of the regolith supporting plant life
and where soil forming processes operate

Geomorphology (9 decks)

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