Transcript Soil Formation

Soil 2 – Soil Formation
 Soil
is formed from the weathering of rocks.
 Weathering: the breaking down of parent
material (rock).
 There are 3 types of weathering:
• Physical,
• Chemical
• Biological.
 The
natural forces carry this out: wind, sun,
frost, ice. Physical breakdown is caused by the
Freeze – Thaw Action phenomenon.
• Igneous and Metamorphic rock surfaces absorb heat
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energy from the sun and in doing so they expand.
By night as the temperatures drop these rocks
contract.
Hairline cracks develop.
Rain gets into these cracks and when it freezes, it
expands up to 9% thus causing the rocks to shatter.
The resulting small particles are called Solum.
 Acid
rain and SO2, CO2, CO, NO3
 Burning fossil fuels e.g. coal, turf, oil, and natural
gas produces Sulphur dioxide. If it combines
with water it forms Sulphuric acid
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SO2 + H2O  H2SO4 Sulphuric acid
CO2 + H2O  H2CO3 Carbonic acid
NO3 + H2O  H2NO3 Nitric acid
 Chemical
breakdown occurs when soluble
components in the rock are dissolved by water.
(A very strong solvent)
 This is further emphasised by various types of
dissolved acids in rainwater.
 Carbonic acid, Nitric acid and Sulphuric Acid are
common in rainwater.
Early plant life like Lichens can breakdown rocks.
 Lichens get minerals from rocks by secreting an
acidic liquid into the rocks.
 This further breaks down the rocks decays slowly.
 When lichens die they also form the first layer of
humus (decaying material) that will eventually
become the soil.
 When the humus becomes a few inches thick, other
plants (like grasses and mosses) can begin to grow
on it.
 The roots of these plants then can break the rock
further.
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 Glaciation
is when snow and ice accumulate in
mountain river valleys and move slowly
downwards due to gravity.
 When glaciers reach lowland areas, they join
together and form larger piedmont glaciers.
 In turn these large piedmont glaciers join
together to form giant ice sheets.
 These ice sheets can cover thousands of kms and
are moving constantly.
 Glaciation has occurred in Ireland in the past
and has contributed to Ireland climate and soil.
 North Europe is said to be in an inter-glacial
period.
 When
glaciers and ice sheets move they scrape
all soil and loose rock from the surface.
 This material becomes mixed in the lower layers
of the ice and are deposited as glacial drift a goof
distance away from its original position.
 This material then serves as parent rock for soil
formation.
 Irelands soils are said to be young because they
are only 12,000 years old.
 There
are 3 types of peats: Blanket, Basin and
Raised peats
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 Blanket
Peats:
• Found in mountainous areas where high rainfall is
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typical (Wicklow, Clare and Kerry to some extent).
Blanket bogs are so called because they form a blanket
over a wide area.
Shallow (1 - 2 meters deep at most).
They do not have as much potential for cultivation by
large-scale machinery or for farming, mainly because
where they are located.
Soils are wet, acidic and infertile.
 Basin
Peats:
• Occurs in land with a depression i.e. a hollow lake or
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river.
Dead remain of plants accumulate at the bottom of the
lake.
The build up of the dead vegation cuases the lake to
close over and become land.
Occurs in water logged and flooded conditions.
Drier and of more agricultural use than blanket bogs
 Raised
bogs:
• Further development of basin bogs.
• They are raised above the level of the surrounding
ground.
 After
the Ice Age, glaciers left a vast amount of
small, shallow lakes around Ireland, these were
taken over by vegetation (plants like reeds and
sedges) growing from the shore inwards.
 Decaying organic matter filled the lake to above
the water level, so it is no longer a lake.
 Trees such as birch and alder and shrubs then
moved in once all the water had gone.
 The areas are then referred to as carr or fen
(fenn) woods.
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These trees would eventually die as well and become part
of the decaying mass.
Organic parent material is formed from half decomposed
plants under very wet anaerobic soils or in lakes; these
conditions prevent the full break down of the plants.
This is referred to as peat parent material and they give
rise to peat soils.
The dominant species at this stage are bog mosses
(sphagnum mosses).
These bog mosses can soak up five times their weight in
water and after thousands of years of Irish weather, these
mosses were able to build up to heights of 10 metres
above the once lake floor.
These bogs are called Raised bogs and are typical of the
midlands.