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The lithosphere and the soil as power equipment and hazard
Soil formation
7.
1. Influences of soil formation
- Parent material
- Climate
- Topography
- Organisms
- Time
Soil formation, or pedogenesis, is the combined effect of
physical, chemical, biological and anthropogenic processes
on soil parent material.
Parent material
Active geological influences
1.Volcanism
2.Tectonics
3.Ground waters
4.Surface waters
Andesite as soil forming rock
Shallow side of aa meandering river
Alluvial plain
A földtani tényezők
Passive geological influences
1. Soil forming rocks
2. Minerals of soil forming rocks
3. Stucture of soil forming rocks
Rendzina – chaarcteristic soil on limestone
Shallow soil on hard rocks
Thick soil on loess
Climate
Climate is the dominant factor in soil formation, and soils show the distinctive
characteristics of the climate zones in which they form. Mineral precipitation and
temperature are the primary climatic influences on soil formation.
Climate directly affects the rate of weathering and leaching. Soil is said to be
formed when detectable layers of clays, organic colloids, carbonates, or soluble
salts have been moved downward. Wind moves sand and smaller particles, especially
in arid regions where there is little plant cover. The type and amount of
precipitation influence soil formation by affecting the movement of ions and
particles through the soil, and aid in the development of different soil profiles. Soil
profiles are more distinct in wet and cool climates, where organic materials may
accumulate, than in wet and warm climates, where organic materials are rapidly
consumed. The effectiveness of water in weathering parent rock material depends
on seasonal and daily temperature fluctuations. Cycles of freezing and thawing
constitute an effective mechanism which breaks up rocks and other consolidated
materials.
Climate also indirectly influences soil formation through the effects of vegetation
cover and biological activity, which modify the rates of chemical reactions in the
soil.
Topography
The topography, or relief, characterised by the inclination of the surface,
determines the rate of precipitation runoff and rate of formation or erosion of
the surface soil profiles. Steep slopes allow rapid runoff and erosion of the top
soil profiles and little mineral deposition in lower profiles.
Organisms
Plants, animals, fungi, bacteria and humans affect soil formation (see soil
biomantle and stonelayer). Animals, soil mesofauna and micro-organisms mix
soils as they form burrows and pores, allowing moisture and gases to move
about. In the same way, plant roots open channels in soils. Plants with deep
taproots can penetrate many metres through the different soil layers to bring
up nutrients from deeper in the profile.
Time
Time is a factor in the interactions of all the above. Over time, soils evolve
features that are dependent on the interplay of other soil forming factors.
Soil is always changing. It takes about 800 to 1000 years for a 2.5 cm (0.98 in)
thick layer of fertile soil to be formed in nature. For example, recently
deposited material from a flood exhibits no soil development because there has
not been enough time for the material to form a structure that further
defines soil. The original soil surface is buried, and the formation process must
begin anew for this deposit. Over a period of between hundreds and thousands
of years, the soil will develop a profile that depends on the intensities of biota
and climate. While soil can achieve relative stability of its properties for
extended periods, the soil life cycle ultimately ends in soil conditions that leave
it vulnerable to erosion. Despite the inevitability of soil retrogression and
degradation, most soil cycles are long.
Human activity
Human activities have had pronounced impacts on soil properties. Conifer
afforestation in the uplands has caused significant decreases in soil pH and in
the quality and turnover of organic matter. Human trampling, while highly
localised, affects sensitive mountain soils in popular areas, leading to loss of
surface organic horizons, and therefore, carbon storage.
Step-working on a hill
Ploughed soil
2. Processes of pedogenesis
Physical weathering
Physical weathering is the class of processes that causes the disintegration of
rocks without chemical change.
Physical weathering on dolomite
1. Thermal stress
2. Frost weathering
3. Pressure release
4. Hydraulic action
Thermal weathering
Physical weathering because of the roots
Chemical weathering
Chemical weathering changes the composition of rocks, often transforming them
when water interacts with minerals to create various chemical reactions.
Chemical weathering is a gradual and ongoing process as the mineralogy of the
rock adjusts to the near surface environment.
dissolution and carbonation - rainfall is acidic because atmospheric carbon dioxide
dissolves in the rainwater producing weak carbonic acid.
hydrolysis - in such reactions, pure water ionizes slightly and reacts with silicate
minerals
oxidation - within the weathering environment chemical oxidation of a variety of
metals occurs. The most commonly observed is the oxidation of Fe2+
(iron) and combination with oxygen and water to form Fe3+ hydroxides
and oxides such as goethite, limonite, and hematite.
Biological weathering
A number of plants and animals may create chemical weathering through release
of acidic compounds, i.e. moss on roofs is classed as weathering. Mineral
weathering can also be initiated and/or accelerated by soil microorganisms.
Humification
The process of "humification" can occur
naturally in soil, or in the production of
compost. The importance of chemically
stable humus is thought by some to be
the fertility it provides to soils in both a
physical and chemical sense. It helps the
soil retain moisture by increasing
microporosity, and encourages the
formation of good soil structure.
Traces of earthworm in soil
Leaching
Leaching is the movement of contaminants, such as water-soluble pesticides or
fertilizers, carried by water downward through permeable soils.
Lime leaching in soil
Argillization
Argillization is used to reduce filtration capacity of fissured, rocky cavernous
strata and of gravelly soils. In this method a clay suspension, with a small
amount of a coagulant added, is inserted under high pressure into the fissures
of the stratum .
Lessivage
Lessivage is a kind of leaching from clay particles being carried down in
suspension. The process can lead to the breakdown of peds (the particles that
give the soil its characteristic structure).
Podzolization
Podzolization occurs in cool and moist climates under pine forests. They are
typical of the colder portions of the humid continental and subarctic climates.
The E horizon is heavily leached and basically composed a of light colored layer
of sand.
Solodization
Most Solonetzic soils have a neutral to acidic A
horizon indicating that some solodization has
occurred. The horizons of salt and lime
accumulation move downward from the B to the C
horizon.
Gleization
Gleization occurs in regions of high rainfall
and low-lying areas that may be naturally
waterlogged.
Gleization in bog soil
Forming of argillic sand laminae
It is a type of concentration in soils. In this case small argillic sand laminae arise
in the ‘B’ horizon during accumulation clay minerals and fine grained sand.
Salinization
Salinization occurs in warm and dry locations where soluble salts precipitate
from water and accumulate in the soil. Saline soils are common in desert and
steppe climates. Salt may also accumulate in soils from sea spray.
Bog formation
Bog formation is a soil-forming process that results in excessive wetting of soil.
Bog formation starts with a change in the water and aeration budgets, an
accumulation of moisture, and the development of anaerobic conditions in the
soil.
3. Functions of soil
Soils perform five key functions in the global ecosystem:
Medium for plant growth
Regulator of Water Supplies
Recycler of raw materials
Habitat for soil organisms
Landscaping and engineering medium
Thank you for your attention!