Saturday, September 24, 2005
GEOG - WEATHERING
Denudation: weathering down of earth’s surface through weathering, mass wasting & erosion
Weathering: disintegration & decomposition of rocks in situ; no transport involved
Mass wasting: movement of surface material down a slope due to gravity
Erosion: wearing away of rocks by moving agents & removal from their original site
Physical: breaking of rocks into smaller pieces
-size & shape altered but not chemical composition
-products are usually coarse & angularmost effective in areas with: 1. little vegetation
2. large diurnal temperature range
3. temperatures fluctuating around 0oC
Types: 1. frost shattering: water that enters the joints in rocks freezes and expands at night, causing stress on the rocks; rock breaks after many repetitions
-angular rock fragments gather at foot of slope to form scree slope
-ice crystals may grow in rock pores
2. block disintegration: splitting of rocks along the joints into blocks
3. exfoliation: outer layer of rocks expand in day & contract at night; cracks are formed, layers peel off
4. granular disintegration: different coloured mineral grains expand & contract at different rates; causes stress & rock will disintegrate grain by grain
5. salt crystal growth: in arid regions; water evaporates, leaving behind salt crystals in rock pores
-grow & swell, causing stress & rock slowly break up
6. hydration: some minerals swell as they absorb water; causes stress & weakens rock. Chemical structure is also changed when this happens
7. pressure release: when overlying rock material is eroded, the intrusive igneous rocks are exposed
-outer parts expand; causes stress; fractures form parallel to rock surface & break away
Chemical: decomposition of rocks when minerals in the rocks react chemically with rainwater, seawater, CO2 & O2 to form new chemical compounds
-alters physical structure & chemical composition
-effective in hot & wet areas
-weakens the rocks that break down over time
Types: 1. solution: more soluble minerals dissolve; parts of rock crumble off
2. carbonation: carbonic acid formed by CO2 & rainwater react with limestone to form a soluble substance calcium hydrogen carbonate
-enlarged & deepened joint: grike
-flat topped blocks btwn grikes: clint
-stalactites on roof & stalagmites on ground
3. hydrolysis: chemical reaction btwn some of the minerals in rocks and rainwater
In granite: consisting of feldspar, mica & quartz
-feldspar changes into clay that crumbles easily
-iron in mica is oxidised; quartz is unaltered
4. oxidation: chemical reaction btwn oxygen in air & water and the minerals in rocks
5. acid rain: rain absorbs sulphuric & nitric acids frm burning of fossil fuels; weathers rocks
Biological: can be a physical or a chemical process
1. roots of trees & plants grow in joints of rocks: exert pressure; widen & deepen them; rock structure loosened; enables other types of weathering to work
2. burrowing animals pry open cracks in rocks: exposes the rocks to other types of weathering
3. overgrazing: soil erosion; rocks exposed
4. humic acids frm decaying plants react chemically
Factors that affect rate & type of weathering
1. rock hardness: depends on minerals in rock
-igneous rocks: hard; sedimentary rocks: softer
-harder rock more resistant to weathering
2. mineral composition: impt influence ovr chemical weathering; some effect on physical weathering
_quartz more resistant to chemical
-basalt rock & limestone less resistant
_darker coloured minerals heat up faster
-darker basalt rocks weather faster physically
3. grain size: coarse grained decompose faster
-granite weather faster than rhyolite
-due to large gaps aft being hydrolysed
4. lines of weaknesses: well jointed weathers faster
-more rock surface exposed to weathering
5. relief: physical weathering more active on steep slopes: landslides; frost action etc on exposed rocks
-less chemical as water flows away more easily
Chemical weathering more active on flat land as water is retained and can act on underlying rocks
-less physical as rocks are sheltered by soil
6. vegetation cover: more weathering
-retains rainwater; humic & organic acid; roots grow
7. human activities: sulphur dioxide & nitrogen oxide acid rain; expose rocks when clearing land dvlpmnt
8. climate: a. temperature: big range > exfoliation
-fluctuate arnd 0oC > frost action
-high evaporation rate > salt crystal growth
-high humidity: water retained
-high temperature > faster rate of chemical
b. rainfall: heavy + high temperature > hydrolysis, carbonation, oxidation, fast plant growth
Weathering: disintegration & decomposition of rocks in situ; no transport involved
Mass wasting: movement of surface material down a slope due to gravity
Erosion: wearing away of rocks by moving agents & removal from their original site
Physical: breaking of rocks into smaller pieces
-size & shape altered but not chemical composition
-products are usually coarse & angularmost effective in areas with: 1. little vegetation
2. large diurnal temperature range
3. temperatures fluctuating around 0oC
Types: 1. frost shattering: water that enters the joints in rocks freezes and expands at night, causing stress on the rocks; rock breaks after many repetitions
-angular rock fragments gather at foot of slope to form scree slope
-ice crystals may grow in rock pores
2. block disintegration: splitting of rocks along the joints into blocks
3. exfoliation: outer layer of rocks expand in day & contract at night; cracks are formed, layers peel off
4. granular disintegration: different coloured mineral grains expand & contract at different rates; causes stress & rock will disintegrate grain by grain
5. salt crystal growth: in arid regions; water evaporates, leaving behind salt crystals in rock pores
-grow & swell, causing stress & rock slowly break up
6. hydration: some minerals swell as they absorb water; causes stress & weakens rock. Chemical structure is also changed when this happens
7. pressure release: when overlying rock material is eroded, the intrusive igneous rocks are exposed
-outer parts expand; causes stress; fractures form parallel to rock surface & break away
Chemical: decomposition of rocks when minerals in the rocks react chemically with rainwater, seawater, CO2 & O2 to form new chemical compounds
-alters physical structure & chemical composition
-effective in hot & wet areas
-weakens the rocks that break down over time
Types: 1. solution: more soluble minerals dissolve; parts of rock crumble off
2. carbonation: carbonic acid formed by CO2 & rainwater react with limestone to form a soluble substance calcium hydrogen carbonate
-enlarged & deepened joint: grike
-flat topped blocks btwn grikes: clint
-stalactites on roof & stalagmites on ground
3. hydrolysis: chemical reaction btwn some of the minerals in rocks and rainwater
In granite: consisting of feldspar, mica & quartz
-feldspar changes into clay that crumbles easily
-iron in mica is oxidised; quartz is unaltered
4. oxidation: chemical reaction btwn oxygen in air & water and the minerals in rocks
5. acid rain: rain absorbs sulphuric & nitric acids frm burning of fossil fuels; weathers rocks
Biological: can be a physical or a chemical process
1. roots of trees & plants grow in joints of rocks: exert pressure; widen & deepen them; rock structure loosened; enables other types of weathering to work
2. burrowing animals pry open cracks in rocks: exposes the rocks to other types of weathering
3. overgrazing: soil erosion; rocks exposed
4. humic acids frm decaying plants react chemically
Factors that affect rate & type of weathering
1. rock hardness: depends on minerals in rock
-igneous rocks: hard; sedimentary rocks: softer
-harder rock more resistant to weathering
2. mineral composition: impt influence ovr chemical weathering; some effect on physical weathering
_quartz more resistant to chemical
-basalt rock & limestone less resistant
_darker coloured minerals heat up faster
-darker basalt rocks weather faster physically
3. grain size: coarse grained decompose faster
-granite weather faster than rhyolite
-due to large gaps aft being hydrolysed
4. lines of weaknesses: well jointed weathers faster
-more rock surface exposed to weathering
5. relief: physical weathering more active on steep slopes: landslides; frost action etc on exposed rocks
-less chemical as water flows away more easily
Chemical weathering more active on flat land as water is retained and can act on underlying rocks
-less physical as rocks are sheltered by soil
6. vegetation cover: more weathering
-retains rainwater; humic & organic acid; roots grow
7. human activities: sulphur dioxide & nitrogen oxide acid rain; expose rocks when clearing land dvlpmnt
8. climate: a. temperature: big range > exfoliation
-fluctuate arnd 0oC > frost action
-high evaporation rate > salt crystal growth
-high humidity: water retained
-high temperature > faster rate of chemical
b. rainfall: heavy + high temperature > hydrolysis, carbonation, oxidation, fast plant growth
# we mugged! @ 7:46 AM 
