EARTH SCIENCES- WEATHERING AND SOIL

Weathering

Physical or chemical breakdown of rock at or near the the surface to create sediment.

Mass wasting (general idea)

A type of way to transport sediment where the material is transported downhill due to gravity

Erosion (general idea)

Transportation of sediment via water, ice or wind

How many types of weathering?

Two types, mechanical weathering and Chemical weathering

Mechanical weathering and its 3 types

Breaks the rock into smaller pieces

1. frost wedging

2. sheeting

3. biological activity

Mechanical sediment

The final product after mechanical weathering where bits of racks vary in sizes

Mechanical Weathering: Frost Wedging and example in Edmonton

Water enters the rocks cracks and when it freezes it expands by 9% thus exerts pressure and breaks the rock.

This is how potholes are formed in Edmonton

Talus

a pile of broken rocks fall due to gravity at the bottom of a cliff/slope side 

Mechanical Weathering: Sheeting

Granite at the surface breaks into sheets and onion like layers

Sheeting is also accomplished due to pressure release and the temperature changing due to the night and day cycle. Where in hot temperatures the outside expands but in cool temperatures the outside shrinks thus it breaks

Exfoliation domes is where sheeting often occurs

Also occurs when crystalline rocks or plutons reach the surface, due to the change in pressure it creates sheeting

Mechanical Weathering: Biological activity

Tree roots breaking rocks or geology students breaking rocks to get samples etc.

Chemical Weathering and factors that affect it

Chemical reaction break up the rocks. Hot and wet environments speed up chemical weathering and it can occur in all environments including polar regions. Morse surface area allows chemical weathering to be more effective

Product of Chemical weathering

End result is chemical sediments where the ions dissolve in water

3 types of chemical weathering

Dissolution, oxidation and hydrolysis

chemical weathering: Dissolution

Because water is polar, the electrostatic forces allows the rock to dissolve the rock. Where the positive end takes the negative end of the rock and vice versa thus breaking down the rock

Pure water dissolves rocks and small amounts of acid can increase dissolution

Chemical weathering: Dissolution examples

Carbonate rocks like limestone(CaCO3) are not soluble in alkali or neutral solutions but do dissolve in acidic solutions.

A weak acid forms when carbon dioxide reacts with water and when its raining this can cause acid rain. (they react midair)

Chemical weathering: Oxidation

main thing is rusting. Rocks like sandstone might contain iron minerals which well breakdown when exposed to the atmosphere. These atoms making the up the minerals in the rocks will separate as the rock rusts away

Chemical weathering: Hydrolysis

hydrogen ions will react with and replace the positive ions like in potassium feldspar. In potassium feldspar, hydrolysis will form clay minerals and potassium and silica ions that’s dissolved in water; making a solution.

Spheroidal weathering

manifestation of chemical weathering where sharp corners have more surface are thus Chemical weathering is more effective here compared to flat surfaces. This produces a smooth shape

Effect of temperature on rock characteristics

Dependant on temperature, different minerals will appear when the rock is formed and these different minerals have different resistance to chemical weathering

Effect of climate on rate of weathering

At different weathering regions (temperature and annual rain), there might be strong chemical or strong mechanical weathering

Sediment Classification

Classified by

1. grain size

2. Minerology of clasts

3. sorting(shapes)

4. Shapes of Clasts(like cubic?)

5. Depositional environment

Sediment Classification: Grain sizes

Classifying the sediment based on the size of bits

1. Boulder >256 mm

2. Cobble 64-256 mm

3. Pebble 4-64 mm

4. Granule 2-4 mm

5. Sand 0.062-2 mm

6. Slit 0.004-0.062 mm

7. Clay <0.004 mm

Sediment Classification: Minerology of clasts

Bits of minerals like the ones we from the first set of notes.

Feldspar, quartz, clay minerals etc, but olivine cannot be found as sediment cause its unstable on the surface

Sediment Classification: Sorting and Roundness

When the sediment is poorly sorted, theres different sizes but if theyre properly sorted then all the sediment is the same size.

Roundness: the sediment can either be

1. angular

2. subangular

3. subrounded

4. rounded

Sediment Classification: Sorting and Roundness process

When sediment gets transported, sorting improves and roundness increases. 

Like in a river all of the heavy sediment is left behind while the lighter sediment gets carried away and as the sediment flows the bits will bump into each other and gets rounded out

Poor sorting implies that the there is a short distance of transport

Sediment Classification: Types of Depositional Environment

1. Continental

2. Transitional

3. Marine

Sediment Classification: Continental environment

Glacial deposits, streams, winds (makes sand dunes) and salt lakes. this environment takes sediment and makes specific sedimentary rocks

Sediment Classification: Transitional environment

Tidal flats, beaches, spits lagoons and deltas

Sediment Classification: Marine environment

Continental shelf- shallow up to 200 m and it includes reefs. Due to the water, you’ll get sediments with different densities.

Continental slope:deeper than 200m includes turbidity

4 common types of sediment

Colluvial sediments, Alluvial sediments, Aeolian Sediments and Glacial Sediments.

Colluvial sediments

Sediment that is transported by gravity and is poorly sorted. Typically is boulder, sand and silt with angular roundness

Alluvial sediments

Sediment that is transported by water and is well sorted. Typically made up of sand, silt and clay

Aeolian Sediments

Sediment that is transported by wind and is usually well sorted. Typically is wind-blown sand, silt and dust. This decreases in particle size.

Glacial Sediment

Sediment transported by ice.

Glacial till

mainly clay that is formed under ice

Moraine

a mixture of boulders, gravel, sand and slay carried on top of ice.

Soil in Engineering

Unconsolidated sediments, regolith (loose stuff)

Mechanically weak and grains are not connected. Usually formed locally or transported elsewhere via erosion

Solids characteristics

Some are compressible, some are incompressible and it comes in various forms

Voids

These are holes in the rocks usually occurs due to a gas/air, and liquids like water, brine or contaminants

Thickness of soil in other regions

1. In the arctic its very thin or non-existent

2. up to 5m thick in mountains

3. thickest in sedimentary basins and along major rivers

Layers of soil

As you go down the layers of soil, you go backwards to the past.The image is the layers of soil here in edmonton.

Soil formation overtime

Initially the surface only had sediments but overtime soil forms at the surface

Regolith layers

Soil and sediment layers are the regolith layers

Soil

It is the interface between the lithosphere, biosphere, hydrosphere and atmosphere. It is the combination of mineral and organic material.

Regolith

Layer of rock and mineral fragments formed by weathering unconsolidated material that is weaker than bedrock (loose rocks)

What does good soil contain?

50% mineral matter and humus(decayed animals and plants)

25% air

25% water

Soil formation depends on

Parent material, Time, Climate, Plants and animals and topography

Parent material effects on soil

influences the rate of soil formation, slower on bedrock but faster on unconsolidated material. The chemistry of the parent material controls the chemistry of the soil and affects the fertility. Different climates can produce different types of soil from the same parental material

Residual Soil

The soil from weathering down bedrock, these rocks can be igneous, sedimentary or metamorphic. This is what is considered to be one of the 2 options for parent material

Transported Soil

comes from unconsolidated material and is transferred from other locations. This is what is considered to be one of the 2 options for parent material

Soil formation: Time

Soil formation takes time and initially the soil composition relies on the parent material but overtime climate has a greater effect and changes the composition

Soil formation: Climate

Most important factor, based on temperature and amount of precipitation, where lots of water means that chemical formation occurs. 

Soil formation: Plants and animals

In forests or bog there is high amounts of organic content while in desserts there is low amounts of organic content, so the types of soil would be different based on what animals and plants there are

Soil formation: Topography

On a steep slope there is a low moisture content and the soil moves downhill so soil does not develop. But in lowlands there is higher moisture and plenty of time for the soil to develop.

Soil profile

Soil formation starts at the surface and moves downwards. The material moves upwards and downwards as soil is formed. The vertical cross section from the surface to the parent material describing all the layers is called the soil profile.

Horizon

Due to the materials moving upwards and downwards, it creates layers called horizons.

Downward sequence of the layers

The downward sequence is O, A, E, B, C where the layers can vary in thickness.

Horizon: O-Horizon

organic material, can vary from dead leaves to decomposed material, full of microscopic life

Horizon: A-Horizon

Can have bits of organic stuff but its made up to 30% of humus (organic component of soil that results from decomposition of plant and animal material) mineral matter layer

Horizon: E-Horizon

Light coloured layer with little organic material. Water in this layer causes the removal of dissolved materials and washes small particles down and other chemicals are transported through leaching (removing soluble substances)

Horizon: B-Horizon

The precipitates/subsoil. All the washed down material from E horizon is here

Horizon: C-Horizon

Altered parent material

3 types of soil

Pedalfer, pedocal and laterite

Pedalfer

The precipitation is greater than the evaporation and transpiration. Means that more water is soaked into the soil resulting in more leaching compared to what gets evaporated. This type of soil develops in humid/wet climates and there’s enough vegetation to produce acid conditions for leaching (Calcium Carbonate is leached downwards due to this acid).

The B-horizon is enriched with iron oxides and aluminum rich clay.

Pedocal

(cal - calcite = calcium carbonate)- this soil is rich in calcite

Precipitation is less than evaporation and transpiration, soil is super dry due to evaporation occurring more than precipitation.This soil is typically found in dry areas with grassland vegetation. Calcium carbonate is not leached downwards in dry lands but it can be drawn upwards and precipitated.

Laterite

The soil is finished after growing something once. Develops in hot, wet tropical climates. Very intense leaching of calcium carbonate and silica. leaves upper soil concentrated in aluminum and iron that gives it a red colour. Minimal humus and not good for agriculture.

other factors that are important, know this diagram

Canadian soil: Chernozemic

Central Alberta has drier climate than northern Alberta so this soil is pedocal. Dark brown-black in colour. Found in cool subarid to subhumid grasslands and forest to grassland transition.

Canadian soil: Luvisolic

Northwest Alberta has wetter climate compared to Rocky mountains isn’t as wet, this soil is pedalfer. Strongly leached A horizon and clay rich B horizon. typically found in deciduous or mixed forests with moderate to cool climate 

Canadian soil: Cryosilic

Permafrost region where mature soil does not develop. Found in the tundra landscape dominated by moss and lichens

Soil Erosion: Nature effect

Water or wind can carry the soil away very easily. It can take years to form but only an hour to get rid of it. This is the impact of rain drops carrying away the soil via flowing water (sheet erosion) 

Soil erosion: Human Effect

Erosion rates are increased by human activity such as plowing can make it easier for water or wind to carry soil away

importance of soil to civil engineers

This is the foundation for their buildings and need to undertsand the strength and other properties

importance of soil to environmental engineers

important when building landfills, water treatment plants and etc. Soil properties control the flow of water and contamination.

importance of soil to Mining engineers

Soil is removed when mining so restoration requires the understanding of the original soil conditions and the soil properties is important to develop strategies to safely construct stuff and minimize contamination.