Soil Formation Flashcards
What is the meaning of sedentary parent materials ?
Parent materials where overlying soils form as a product from the weathering of underlying rocks are called sedentary parent materials.
What is the meaning of Transported parent materials?
Parent materials carried in from elsewhere are called transported parent materials, for example, alluvium, where the rock has weathered elsewhere, and then carried by water to be deposited and form new soils.
What rocks are classified as sedentary materials?
Igneous rocks from molten lava;
Sedimentary rocks from consolidation of particles derived from weathering of other rocks or chemical deposits;
Metamorphic rocks from changes in either of the above by heat or pressure.
What four forms of Igneous Rocks are there?
plutonic acid = granite
plutonic basic = gabbro
volcanic acid = rhyolite
volcanic basic = basalt
What forms of sedentary rocks are there?
mudstones/shale (from clays);
siltstones (silt);
sandstones (sand);
conglomerates (cemented gravels).
What are metamorphic rocks?
These are formed when igneous or sedimentary rocks have been melted by heat or pressure near a volcano or as the earth’s crust bends. Metamorphic rocks are characterised by layering but the layers are often irregular and frequently contain clearly distinguishable crystals, for example, schist, gneiss. Hardened shales are slates.
What are the modes of transport for Transported parent materials?
water
wind
gravity
ice
What are water deposits called?
Water deposits are alluvium and lake deposits.The soils developed from alluvial parent materials have the following features:
Rounded stones and sand particles due to abrasion in the stream;
Layers of different texture. As you dig into the soil, you may observe many and rapid changes in soil texture, for example, sand layers between clay layers. The different layers are deposited depending on the type of material being transported by the creek or river;
Buried layers. Old soils originally at the surface which had organic matter can be covered by subsequent deposits. Hence organic rich layers exist in the subsoil.
What are wind deposits called?
Wind transported materials form aeolian deposits.
Wind lifts particles from the soil surface. Only particles or aggregates that are greater than clay size (silt and sand sizes) can be lifted from the soil surface.
What is Gravity affected soils called?
The material moving downslope under the effects of gravity combined with some water flow is called ‘colluvium’.
The soils that develop from colluvial parent material have:
Buried organic layers
angular broken rock fragments, and
layers of different texture.
How does ice transport soils?
The material either carried on the surface or within the ice produces:
Glacial till - mixed textures but compacted, so poor drainage properties.
glacial outwash - materials deposited by the water melting from the glacier.
What are the four soil formation types?
Transformation (minerals to different sizes and composition) i.e. weathering;
Translocation (or transporting materials through the developing soil); i.e. leaching;
Additions
Losses
define the meaning of Transformation in soils.
Weathering is the physical or chemical alteration or transformation of the parent material.
What are the two types of weathering that occur?
Physical
Chemical
What are the 4 types of physical weathering?
Temperature
Water
Wind
Plant roots
How does temperature affect rocks?
The different minerals present in rocks heat and cool at different rates. This heating and cooling causes expansion and contraction respectively of the minerals. Because minerals change size at different rates, stresses build up in the rock that can result in fracture (the particles get smaller). The greatest changes occur at sunrise and sunset especially in arid environments. In colder climates, the effects are associated with freezing and thawing of water in cracks in rocks.
How does water effect rocks?
Water transports sand and silt particles as it flows. This suspended material abrades rock fragments reducing particle size. This action is particularly noticeable in coastal environments where wave action occurs.
How does wind effect rocks?
In arid areas, wind transports particles that again abrade rocks.
How do plant roots effect rocks?
Once plants become established, roots grow into cracks in rocks. As the roots enlarge during growth, the cracks are enlarged until fracture occurs.
What is chemical weathering?
This type of weathering depends on the reaction of water molecules with the various rock minerals. These reactions normally result in;
The alteration of rock minerals to soil minerals;
the reduction in particle sizes;
the release of plant nutrients in soluble, that is, plant available forms.
What are the 6 chemical forms of weathering in rocks?
Dissolution Hydrolysis Hydration Oxidation/Reduction Carbonation Chelation
What is dissolution?
Some of the rock minerals dissolve in water and can be removed in water percolating through or flowing over the rock.
What is Hydrolysis?
This is probably one of the more important reactions. In this reaction, the small concentration of H+ present in water reacts with the rock minerals releasing Ca2+, Mg2+, K+ and Na+. The OH- fraction of the water may react with the cations that are released
What is Hydration?
Water is added to the structure of the minerals in the parent material. This is different from hydrolysis as the water does not have to be present as H+ and OH- for this reaction to occur.
As layer silicate minerals such as mica hydrate, they expand. This enables more water to enter the crystal allowing other reactions to occur.
