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68 Cards in this Set
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- Back
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What is weathering? |
The in situ alteration and breakdown of earth-forming materials |
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What does weathering do? |
Reduces the strength of rocks allowing erosion forces to remove and transport material (creates soil - vital to human existence) |
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What are the types of weathering? |
Granular disintegration, crumbly disintegration, flaking, contour scaling, exfoliation, and spheroidal weathering |
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What is granular disintegration? |
Rocks broken into their component crystal units producing course grained and sand or gravel pitted rock surfaces. Typical of granite, sandstone and conglomerate |
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Crumbly disintegration |
Detatchment of large rock fragments |
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Flaking |
Small thin flakes or chips peel off a rock surface |
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Contour Scaling |
detatchment of one or more plate-shaped layers several cm thick parallel to rock surface |
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What are flaking and scaling the result of? |
cycles of heating, cooling or wetting and drying |
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Exfoliation |
large scale peeling of successive concentric layers from an inner core |
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Spheroidal weathering |
spherical boulders formed because of edges and corners of rock weather flat surfaces. (Joints in rock) |
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What is the weathering process? |
Rocks formed in crust under heat and pressure (no air or water). Rock gets near to surface (cooler and low pressure) and is exposed to air, water, biological organisms which causes a disequilibrium that leads to rapid weathering. |
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Where on the surface is there less weathering? |
Below the water table |
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What is mechanical weathering? |
Breakup into smaller materials without changing chemical composition |
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Effects of mechanical weathering |
- Small pieces have greater surface area, subject to chemical weathering - Permeability of rocks may be increased |
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What is unloading? |
Reduction of confining stresses allow mineral grains to move farther apart Expansion divides the rock into sheets along cracks parallel to surface (in cliff). Cracks trigger rock falls that provide a + feedback loop for further slope retreat |
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What does unloading create? |
Convex hills or domes and controls shape of valley side |
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What is a rock blister? |
a short slab of rock that expands and arches upward from parent rock |
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Spalling |
Irregular or lozenge shaped rock fragments break from the walls of a cave or tunnel |
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How is a pedestal rock formed? |
Vertical fractures allow lens shaped fragments to detach thereby gradually reducing the thickness of the base |
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What does Frost do? |
Frozen water expands and puts pressure on the rock (splits apart). Depends on speed of temp change, amount of water (porous rock can absorb expansion) more likely with smaller grain size |
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How does salt cause mechanical weathering? |
Crystals settle in small spaces in rocks and generate destructive pressures when water is absorbed. Salt expands with + temp more than rocks. It crystalizes, increasing volume. (wind carries sea spray in coastal areas - more common) |
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What effect does heating and cooling have on rocks? |
Rapid increase in temps from fires can explode rocks |
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What are clays particularly effected by? |
Wetting and drying. |
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What is chemical weathering? |
Rock minerals change chemical compound. Soluble components removed causing cavities that weaken rocks. Some changes cause increases in volume causing rock to crack. Some changes strengthen rock. Rate of change determines significance of weathering. |
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What are chemical reactions aided by? |
The seperation of water into H+ and OH- ions which change its acidity (pH value) |
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What are the 7 types of chemical reactions for chemical weathering? |
1. Hydrolysis: Dominant in ig bc it causes decomposition of silicates (most common min on earth) e.g, feldspar breaks down when water and H+ ions displace potassium ions which are then washed away. |
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What are the 7 types of chemical reactions for chemical weathering? |
2. Cation exchange: Substitution of Hydrogen ions in solution for those in mineral. E.g. (Mg2+) calcium (Ca2+), Sodium (Na+), Potassium (K+). Temp, acidity and organic content of solution affect rate of change. EG when Magma cools different minerals solidify at diff temps. Those that solidify at higher temps more unstable than those that solidify at cooler temps. |
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What are the 7 types of chemical reactions for chemical weathering? |
3. Oxidation: Reaction between substance and oxygen that forms oxides or hydroxides if water is present. Iron changes to rust. Pyrite oxidation creates sulphuric acid which can then react wit calcium carbonate to form gypsum. Eg. |
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What are the 7 types of chemical reactions for chemical weathering? |
4. Reduction: The opposite of oxidation when a substance adds electrons. In waterlogged conditions with little oxygen available or where there is an abundance of organic material, bacterial carry out reduction |
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What are the 7 types of chemical reactions for chemical weathering? |
5. Carbonation: Reaction btwn minerals and carbonate or bicarbonate ions. When CO2 dissolves in water it forms carbonic acid. Water becomes more acidic. Increases breakdown of feldspars and silica but decreases breakdown of iron |
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What are the 7 types of chemical reactions for chemical weathering? |
6. Hydration: water is held by mineral structure. Prepares minerals for alteration by other chemical processes - important in formation of clays. Increases volume of mineral allowing physical breakdown. Reaction reversed by heating w/o any chemical change |
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What are the 7 types of chemical reactions for chemical weathering? |
7. Solution: The complete dispersal of mineral ions in water particularly gypsum, carbonates and salt. Limestone is most soluble of common rocks in carbonic acid. Calcium carbonate (acid rain) becomes calcium bicarbonate (very soluable). |
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When does oxidation occur? |
Oxidation occurs through the presense of dissolved Ox in H2O in the aerated zone above the water table. A substance loses electrons in alkaline environments such as sandstone, limestone and shales rather than ig or meta rocks |
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What is unconsolidated material? |
A mix of minerals that resisted weathering, new materials created by weathering (clay, oxide, hydroxides of iron (hematite), aluminum (bauxite), silica, titanium, and organic matter. |
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What are the factors that determine weathering of rocks? |
1. Composition |
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What are the factors that determine weathering of rocks? |
2. Size, shape and degree of perfection of crystals |
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What are the factors that determine weathering of rocks? |
2. Access of weathering agent |
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What are the factors that determine weathering of rocks? |
3. Rate at which weathered product is removed |
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What are the factors that determine weathering of rocks? |
4. Texture, degree of fracture, strength of bonding |
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What are the factors that determine weathering of rocks? |
5. Porosity, permeability, ability to hold water |
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What are the factors that determine weathering of rocks? |
6. Rock dip, bedding plains, joints and faults (affect water's ability to travel through and evacuate soluble products) |
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What are the factors that determine weathering of rocks? |
7. Discontinuities, small grain size, cracks exposed to weathering and increase efficiency of chemical weathering |
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What are the factors that determine weathering of rocks? |
8. Position of site (drainage) |
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What are the factors that determine weathering of rocks? |
What rocks are located near each other (PG 112) |
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How does Silicate weathering play a role in stabilizing the earth's temps? |
(-) feedback loop - Increase temps increase silicate weathering which removes CO2 from atmosphere in it's process |
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What is biological weathering? |
Biophysical or biochemical processes associated with living matter. EG. Worms and burrowing animals mix soil and expose new material to weathering - allowing air and water and organix matter to go deeper. Animals breath underground increasing CO2 levels. |
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How does bacterial play a role in biological weathering? |
Bacteria are plants with single cells. Most break down the complex carbon compounds of veg and some oxidize sulphur, iron and other minerals. EG Acidic min water in Eliot Lake allowed for recovery of uranium - bacterial oxidation |
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Plants and biological weathering |
Algae, lichens and fungi hold thin film of water against rock surface. Breakdown of organic matter in soil promoting mineral ion exchange. Roots force rocks apart |
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Weathering and climate |
Weathering is affected by temp, precip, wind, cloud cover, humidity, length of snow cover, aspect (N or S facing). Long-constant gentle rains are more effective at weathering than downpours or wet/dry periods. Some say site specific characteristics are more important than climate. Weathering hard to identify. |
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Almost all exposed rock is covered by a thin coating,what are they made of? |
Silica glaze in desert environemtns and derive from clay weathering. Rust coloured iron films are common in many climates |
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What is case hardening? |
When chemical weathering softens the interior of igneous rock and grain cement builds up on sedimentary rocks. The soft material is removed - Tafoni are fomed |
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What are tafoni? |
Small cave like features on granular rock like sandstone and granite. |
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What are honeycombs? |
found in sandstones in many different climates. Causes may be numerous |
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What are duricrusts? |
Hard crust on land surface making it hard to cultivate and low fertility. Found in tropics. Laterite is most common |
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How deep can weathered material settle if not removed by erosion? |
up to 100m - in most climates. Takes millions of years to form |
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What does the soil profile consist of? |
O- organic material on tip A - primarily formed by leaching of organic matter B - larger portion is mineral material C - nearly all weathered mineral material |
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Different climates have different profiles |
Grassland: chernozems (brown to dark black) Poor drainage - peat (bluish-grey clay) |
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Different climates have different profiles |
Coniferous forest: podzols (grey) Tropical Forest: Ferralization (reddish) |
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What is key to soil value for ag? What soil is best? |
Clay and loam |
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What are the types of soil structure? |
Granular, crumb, platy, prismatic, massive, columnar, blocky, small grain |
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What is the soil catena? |
The slope. Can have same development opportunities but different slope has different drainage which causes variations in soil type. Midslope soils thinner than bottom, steeper slopes better drainage than flatter. |
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What forms soil? |
Weathering, breakdown of organic matter, movement of matter up and down profile via water and soil organisms, accumulation of material in situ (look at text) |
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How many categories does the Canadian soil order system have? |
10 - reflect climate conditions |
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How does soil related to geomorphology? |
It sits btwn the surface and bedrock and reflects the geomorph changes that took place over time, including slope and drainage. |
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What soils are more resistant to erosion? |
Soils with faster infiltration rate and more organic matter. Rather than sild sand or clay |
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What types of erosion are slopes lacking ground cover subject to? |
Rain spalsh and surface runoff. May be either sheetwash or rill and gullies |
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What is an important factor for soil erosion? |
Rain intensity. Tropics have heavier rainfall than cooler areas |
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How can erosion be measured? |
By catching sediment as it runs off the area under study. Or pole marking the surface at a set time. |
