Midterm 2 Flashcards
In what ways are soils important in other spheres? (4)
- Energy budget
- Hydrology (percolation and evapotranspiration)
- Nutrient movement
- Carbon cycle
Summarize the geologic cycle
- Magma is in the asthenosphere
- Magma can either build crust or reach surface and cool
- Tectonic plates are responsible for movement of magma, and heat and pressure that transforms rocks
- Rocks are formed by cooling magma
- Can then be transformed in many ways
Define the three types of rocks
Igneous: composed of minerals formed from molten magma
Sedimentary: composed of minerals weathered from other rocks
Metamorphic: formed from secondary pressure/temperature processes
What are the two classifications of igneous rocks?
Intrusive: these cool in Earth’s surface
Extrusive: these cool outside
Describe the differences in intrusive and extrusive igneous rocks and give examples
Intrusive develop larger grain sizes because these cool slower (granite, diorite)
Extrusive cool much faster (obsidian, pumice, basalt
Describe general patterns of rock types across Canada
Much of eastern & parts of Northern Canada is covered by the Canadian shield, which is mostly igneous rock
Prairies towards the west are generally sedimentary
What crystals is granite made of?
Feldspar, quartz, mica
Define mineral. How are they formed, and where can you find them?
- inorganic natural solid compound with specific chemical formula and crystalline structure
- formed at high temperature and pressures in crust
- in igneous and metamorphic rock
Describe the structure of a mineral tetrahedral
[SiO4]4-
- silicon surrounded by 4 oxygen with negative charge
List and describe the different mineral formations. (5)
Olivine - island, tetrahedrals form clusters (no Si-O-Si), bond w Fe/Mg
Pyroxene - chain, 2 shared, and 2 unshared oxygens (50%)
Amphibol - double chain, some share 2 O and some 3 (62.5%)
Mica - sheet, sequences of chains where 3 O share (75%)
Quartz - 3D structure, 100% Si-O-Si
What is an isomorphous substitution?
replacement of central Si with Al (has different valence)
results in aluminosilicate minerals
now must incorporate a cation
Examples of feldspars (3)
Albite - Na addition
Anorthite - Ca addition
Orthoclase - K addition
Give an example of an acidic rock, a basic rock, and an ultrabasic rock.
Acidic - granite, rhyolite
Basic - gabbro, basalt
Ultrabasic - peridotite
Describe the bond strengths in different element-O bonds
From strongest to weakest, and most resistant to easily weathered
- Si-O-Si
Al-O-Al
Fe/Mg-O
Na/K/Ca-O
Define and describe felsic and mafic rocks.
Felsic - high in silica, light, lower melting point, highly resistant to weathering, generally contain potassium and sodium, more quartz and feldspar
Mafic - mostly magnesium and iron, darker, high melting temp, low weathering resistance, more pyroxene and olivine
Define sedimentary rocks.
Particles that have been weathered, eroded, and transported and cemented together
What are the 4 processes/sources of sedimentary rocks?
Weathering and erosion of existing rocks (sandstone)
Accumulation of shells on ocean floor (limestone)
Accumulation of organic matter of ancient plants (coal)
Precipitation of secondary minerals (CaCO3)
What are the 5 stages of sedimentary rock formation?
Weathering - generation of particles
Erosion - removal of particles from parent material
Transport - dispersal of particles and ions
Deposition - settling out of transporting fluid
Lithification - transformation into solid rock
What are the 6 clast sizes?
> 80 mm - boulders and cobbles - conglomerate (breccia)
2mm - pebbles and gravel - conglomerate
0.5-2mm - sand, sandstone
0.062-0.5mm - sand, sandstone
0.0039-0.062mm - silt, siltsone
<0.0039 - clay, shale
Describe chemical sedimentary rocks and give 5 types.
new minerals formed in situ
Limestone CaMg(CO3)2
Evaporites - Na and Ca chlorides and sulphates
Ironstone - oxides and hydroxides of Fe and Al
Hydrothermal deposits (black smokers)
Organic - coal, oil
What are metamorphic rocks? How are they formed?
rocks created by transformation of igneous and sedimentary rocks
- Heating
- Pressure
- Heating + pressure
- Compression and shear
usually harder and more resistant to erosion than parent
What is weathering and what are the two main types?
Breakdown of rocks and minerals
Physical - physical disintegration of rocks and minerals, decreasing particle size and increasing surface area
Chemical - transformation of minerals into new products
4 types of physical weathering
Freeze thaw
Thermal changes
Salt weathering
Biological
Chemical Weathering (6)
Direct solution - dissolution of soluble salts
Ex. Na and K, Cl and SO4
Hydration - Minerals absorbs water, then mineral disintegrates & forms new mineral
Ex. hematite to limonite or anhydrite to gypsum
Redox reactions - change in element valency
Ex, iron, Fe2+ <-> Fe3+
Chelation - reaction of normally insoluble elements (ex. Fe, Al) with complex organic compounds produced by decomp of organic matter
Carbonation - reaction of carbonic acid H2CO3 with carbonates
H2CO3 produced by dissolution of CO2
Results in soluble product
Hydrolysis - reaction of H+ ion with cations in minerals
Very important process
We see lots with acidic rain
H+ from CO2 dissolution in water or from acid rain
What impacts the rates of weathering?
- intensity of weathering processes and strength and resistance of minerals
- strength -> igneous > meta >sed
How does weathering intensity change?
Physical facilitated by freeze thaw cycles, variations in water content, temp, and biological activity
Chemical weathering facilitated by high temperatures and high biological activity, production of organic acids and CO2 in soil, and acidity (ex. Acid rain)
Explain the weathering climate diagram
- strong chemical if high rain and high temp
- strong physical if slightly drier and cold
- moderate chemical if mid both
more physical towards cold and dry and more chemical towards hotter and wetter
How were monteregian mountains formed?
Magma that never reached surface, was covered by sediment, then this was uncovered and eroded and is now igneous mountains
How are soils formed?
Bedrock disintegrated by physical processes
Becomes parent material
Organic materials come in and advance soil formation (chemical weathering)
Organic matter begins to accumulate, eventually see horizons
horizons continue to develop
Describe the typical soil profile
O horizon on top - only organic matter
A horizon - mix organic and minerals, very dark
E - transition between A and B - pale
B subsoil, brown
What are the 4 soil forming processes?
transformations - organic matter to humus, primary minerals turning to compounds
transfers - up and down, humus clay ions out, ions in
- caused by capillary rise
removal - leaching and erosion
additions - precipitation, ions, organic matter
5 soil forming factors
parent material (sediment type, minerology, ease of weathering)
climate (temp, precip)
time (older soils more developed)
organisms (habitat type and vegetation)
topography (controls water regime and rates of soil erosion)
- humans also important
How does climate effect soil formation?
- high temps and high precip, horizons deeper
savanna shallow
polar desert little chemical alteration and soil shallow
Describe differences in profiles for prairie vs forest
Prairie - thick A horizon, both A1 and A2, has Ck layer
Forest - thin A horizon, E horizon present
How does topography control soil moisture regimes?
top of slope - free drainage
middle of slope - restricted drainage
bottom - poor
Describe soil texture
defined as mixture of gravel, sand, silt, and clay particles
what is the importance of soil texture
soil infiltration rate - overland flow and erosion
soil permeability - drainage
water capacity of soil - water for transpiration
soil structure - root growth and aeration
cation capacity for retention - supplies for plants and buffer to acid rain
What binds cations in soil?
clay, needs H+ from carbonic acid from plant to release ions
NPP in different ecosystem
NPP higher in more productive ecosystems, so lower soil organic matter
Organic output is controlled by:
Temp and precip - higher = faster decomp
Type of plant tissue - rich in N and P decomp quickly
Soil properties - fertility, texture, fauna
Importance of organic matter in soils
improves structure and porosity
increases infiltration rate
increase available water capacity
supply nutrients to plants thru decomp
humus has high cation exchange capacity
What is ethnopedology?
Studying how different cultures around the world describe soils