(5) + (6) Weathering Flashcards
1
Q
Weathering
A
- Breaks down rock into loose particles : Creates sediment & soil & dissolved ions in water
- Change phys. & chem. character of rock
- Surficial process
- Leads to development of sediment & sedimentary rock : Major Earth material at surface ; Minor in total Earth crust
2
Q
Two types of weathering
A
- Mechanical (or) Physical [physical disintegration, no chemical change]
- Chemical (rock decomposes due to exposure to water and gases in atmosphere)
3
Q
Weathering Is progressive
A
- Weathering along joints (fractures)
- Rounded corners
- Increases towards the surface
- Greater surface area speeds weathering
4
Q
Mechanical Weathering
A
- Intact rocks break into pieces
- Major types:
- Frost action **
- Pressure release **
- Plant growth (roots in the cracks of rocks)
- Burrowing animals (burrow into the rock)
- Temperature changes, expansion and contraction (fire suddenly put out, hot interior, cool exterior causes them to explode)
5
Q
Frost Action
A
- Freeze-thaw cycle
- Expanding water when it freezes
- Boulders created by frost wedging
6
Q
Pressure Release
A
- Most effective of mechanical weathering
- The rock breaks apart along these joints and exfoliates
- Rock breaks into sheets
7
Q
Where will mechanical weathering be most intense?
A
- Cool, with abundant water (Freeze thaw)
- Steep slopes (Gravity assists)
8
Q
Chemical Weathering
A
- Also ‘rock decomposition’
- Rocks react with water and air to produce new chemical products (Makes new minerals and ions in solution. Many of these reactions prefer warm, wet conditions)
- Remember equilibrium? (Will break down without it. Mineral stability)
9
Q
Agents of chemical weathering (Oxygen)
A
- Interaction of water with rocks
- Abundant in atmosphere: chemically active (oxidation)
- If Fe present, yields Fe-oxide and Fe-hydroxide minerals
- If Al present, yield Al-oxide minerals
10
Q
Agents of chemical weathering (Carbonic Acid)
A
- Most important natural source of acid: carbon dioxide dissolved in water
- Weak acid, but abundant
Rainwater; water percolating through soil - Aids dissolution (dissolving minerals)
- Aids hydrolysis (breakdown of minerals from reactions with water)
- Can cause the formation of new minerals
11
Q
Chemical Weathering: Calcite
A
- Form caves
- Discolour and dissolve marble and limestone statues, monuments
- Where do the ions go?
• Hard water
• Seawater is a product of weathering carrying dissolved ions into the ocean
12
Q
Chemical Weathering: Quartz
A
- Forms smaller particles of quartz +
- Dissolved silica ion
• Forms common cement in sedimentary rock - Quartz is rock-forming mineral LEAST susceptible to chem weathering
• Strength of bonds in crystal lattice
13
Q
Chemical Weathering: Feldspars
A
- Clay minerals +
- Ions of SiO2, NA, Ca, K
• Note cations from K-feldspars and plagioclase: Na, Ca, K
• Effects of carbonic acid
• Slow, complex reaction
14
Q
Chemical Weathering: Ferromagnesian minerals
A
- Clay and minerals +
- Ions of SiO2, Mg, Na, Ca, K +
- Fe oxide minerals
15
Q
Yellowish-reddish soils are rich in Fe oxides (examples)
A
- Limonite, goethite (yellow)
- Hematite (red)
16
Q
After complete weathering what is left?
A
- Solids: Clays, quartz, iron oxides, aluminum oxides
- Ions : including Ca2+ SiO2, HCO-3
o Ions become cement for sediment reactions
o Calcite, silica common elements
17
Q
Chemical weathering and climate
A
- Most intense where there is abundant liquid water
- Most intense where warm
18
Q
Soil
A
- Layer of weathered, unconsolidated material on top of bedrock
o Some definitions: Contains organic matter and can support plant growth - Role of clay, quartz
o Clay holds water plant nutrients
o Quartz: sand grains drainage
19
Q
Mature soil is layered (soil horizons) in…
A
Appearance and chemical composition
20
Q
Soil Formation
A
- Takes long time to form (thousands of years)
- Depends on:
o Climate: (rainfall, temp)
o Parent rock composition
o Organisms (type of vegetation, different root systems)
o Relief (slope, topography)
o Drainage
o Time
21
Q
Soil Formation: Climate
A
- Most important factor determining soil type
- Dry climate
o Thin soil
o Little leaching
o Little humus
o Upward movement of soil water (Evaporation and Capillary action) - Wet climate
o Form thicker soils
o Strong leaching
o Downward movement of soil water
o High Al and Fe oxides
o Abundant humus
22
Q
Bauxite (Aluminum Oxide)
A
- Least soluble of all the weathering products
- Source of aluminum
- Formed in tropical weathering conditions
- Laterite soils
- Highly leached
- Only insoluble oxides remain
23
Q
Weathering produces: Sediment
A
- Loose, solid particles
- Classified by size:
- Gravel (includes boulders and cobbles)
- Pebbles
- Sand
- Silt
- Clay
- (mud = wet silt and clay)
24
Q
Transportation of Sediments: Agents of transportation
A
- Running water
- Glaciers
- Waves
- Wind
25
Q
Transportation of Sediments: Rounding
A
- Particles hit and scrape each other during transport
- Gets rid of irregular surfaces
- Rounding vs angular (gradational)
26
Q
Transportation of Sediments: Sorting
A
- By size
- Poorly sorted well sorted (mixing of sizes uniform) sizes
- Running water – a good sorting agent
27
Q
Deposition of sediment
A
- Transported materials settle
o Occurs when agent loses energy and can no longer transport its load - Chemical or organic sediment accumulates on the sea or swamp floor
o Dead organisms accumulate
o Evaporation and precipitation (ex. Salt))
o Change in temperature, pressure, chemical of solution – can cause precipitation
28
Q
Preservation of sediments
A
- Not all sediments are preserved as sedimentary rock
o Marine sediments most easily preserved
29
Q
Lithification of sediment
A
- Process that converts loose sediment into sedimentary rock
- Compaction and cementation (results in clastic sedimentary rock)
o Pressure
o Usually buried under more sediment - OR crystalize minerals directly from solution (chemical sedimentary rock)
