Climate and Weathering Flashcards
(32 cards)
1
Q
Climate
A
Refers to characteristics atmospheric conditions over a long period of time
- years or decades
2
Q
Weather
A
Refers to atmospheric conditions over short periods of time
- days or weeks
3
Q
Influences on weathering
A
- rock type and structure
- topography
- presence of organisms
- age
4
Q
Climate imposed effects of weathering
A
- style
- rate
- volume
- products
- landscape
5
Q
Weak leaching
A
smectite
6
Q
Moderate leaching
A
kaolinite
7
Q
Intense leaching
A
Gibbsite
8
Q
Peltier (1950) scheme
A
Weathering rates related to temperature and rainfall
- intensity of chemical weathering
9
Q
Weathering
A
breakdown of rick by;
- mechanical
- chemical
- biological
10
Q
Functions of weathering
A
- give rock lower strength and greater permeability
- produces landforms
- releases minerals in solution
11
Q
Mechanical weathering
A
- Progressive breakdown
- increases surface area of the rock for chemical weathering
- fatigue, repetition of stress
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
13
Q
Frost action (Mechanical)
A
- physical disintegration (frost shattering
- cold environments, cyclical freezing
freezing = 9% increase in water volume
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
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
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
- they wedge their tiny
- 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
Reduction (Chemical)
- 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
Biological weathering
root penetration = bio-mechanical
- lichen growth or guano = thermal weathering
- coastal organisms bore and graze
- bacterial chemical secretions (alter minerals)
animal burrowing etc.
27
Tor formation
* 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
Weathering landforms
```
Tors, Dartmoor (280Ma)
• Granite batholith cooled
• Composition – Quartz,
feldspar, biotite mica
• Cooling to initial vertical
cracks
• Faulting accentuated jointing
```
29
Continued weathering of profile
```
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
Human activities (Biological)
- quarries, dams, roads
- climate change;
- increased rainfall
- warmer temps
- chemical emissions
- land clearance;
- forestry and grazing land
31
Final stage of tor formation
```
• Quaternary glaciation
• Too cold for chemical
weathering
• Mechanical processes
take over (Freeze thaw/Solifluction in
permafrost)
• Removes weathered
debris
• Soil and boulders
```
32
Soil?
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
