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SGL12803: Introduction to Soil Geography summary lectures and book
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Summary of lectures and book of the course Introduction to Soil Geography
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INTRODUCTION TO SOIL • . . . = other factors that influence soilformation locally, but not universally
GEOGRAPHY: A SUMMARY OF Pedon: the 3D unit that is to characterize an
THE LECTURES 2019-2020 P2 individual soil.
• It is the smallest spatial unit of a soil
CHAPTER 1: WHAT IS SOIL? displaying the full range of properties that are
characteristic for a particular soil.
SOIL DEFINED • A pedon usually occupies about 1 to 10 m2
clay < 0.002 mm of land area.
silt > 0.002 mm and < 0.05 mm • Serves as the fundamental unit of soil
sand > 0.05mm and < 2 mm
classification.
gravel > 2 mm
Polypedon: a group of very similar pedons.
Soil: unconsolidated mineral + organic matter
• It is recognized as a landscape component
that is/was at the Earth's surface
large enough to be called a soil individual.
Soil science: the science of the properties
and functions, as well as the development and
distribution of soils. THE GLOBAL SIGNIFICANCE OF SOILS
Pedology: the study of soils ecosystem services:
Soils are found at the interface between the 1) provisioning: material and outputs
biological, hydrological, lithological and from ecosystems
atmospheric spheres of our planet. 2) regulating: ecosystem is a regulator
1. Atmosphere: Gases, CO2, O2, N2 3) supporting: living space, organism
2. Biosphere: Plants, animals, microbes, their diversity
products and remains. 4) cultural: non-material benefits
3. Lithosphere: Minerals in rocks, clays, (The 7 soil functions (don’t need to know)
sediments.
4. Hydrosphere: Water and dissolved CHAPTER 2: GEOLOGICAL
substances. PROCESSES, PARENT MATERIALS
5. Pedosphere: the soil covering most of the AND LANDSCAPES
earth; where the atmosphere, biosphere,
lithosphere and hydrosphere meet ORIGIN AND COMPOSITION OF THE
Soils develop in unconsolidated (consolidate = EARTH’S CRUST
make something physically stronger or more The earth’s crust (lithosphere) consists of a
solid) parent material. The origin of this parent thin layer of cold solid rock that floats on the
material is bedrock, weathered under the molten liquid rock (magma) – Crust (+- 5-50
influence of biota and climate. km) – Magma (208km)
Regolith: the layer of unconsolidated material Litoshpere:
and weathered rock resting upon solid ➢ Oceanic crust (5-10km) heavy, Fe-rich:
bedrock (vary in thickness between 100-101) basalt
Soil forming factors (interact > result soil) ➢ Continental crust: (5-50km) light, SiO2-
1. Climate rich: granite
2. Organisms
3. Relief or topography GEOTECTONICS AND VOLCANISM
4. Parent material Continental drift and plate tectonics
5. Time ➢ The earth crust consists of lithospheric
The CLORPT model: plates that are moving, floating on the liquid
Equation: S or s = f (CL, O, R, P, T, . . .) mantle magmas. This moving is called
• S = soil type continental drift and is driven by convection
• s = soil property flows inside the mantle.
• CL = climate ➢ The plate movements can be converging
• O = organisms
causing mountain building, or diverging
• R = relief
breaking up a larger plate in continental rift
• P = parent material
systems. If the rift system is successful, a new
• T = time
ocean will open up with a diverging spreading
center: the mid-oceanic ridge.
,➢ When plates converge, the more heavier Basalt can flow over large distances -> shield
plate moves below the lighter one in a volcanoes consist of many thin layers basalt
subduction zone. The geological processes When more pressure during the eruption:
of moving plates are called plate tectonics. formation of scoria or cinder cones.
➢ Rift valley formation (tears->plates apart-
>ocean forms (with mountain underwater) (2) Andesitic volcanism
➢ Ridge between two plates; the further the - more viscosity (magma flows less easily)
ridge the older it is - gasses escape less easily -> higher P ->
First continent: Pangea more explosive
Knowledge of the earth’s crust is based on - smaller quantity lava flow -> smaller distance
remote sensing– Core of the earth consists flow
of iron (Fe). - stratovolcano/composite cone
Pieces of the earth’s crust: - pyroclastic flows (a dense cloud of hot
➢ Lithospheric plates gasses with rocks + lava of acid magma
o Oceanic, continental or combination of both. forming pumice)
o Move 2-15 cm/year Stratovolcano: convex steep slopes, layered
Mountain building: buildup of different phases of ash fall, lava
➢ Converging plates form mountain belts, the flows, cinders (scoria) and pyroclastic flows.
process of mountain building or orogenesis Composite cone:
(process in which a part of crust is deformed
by lateral compression and form a mountain (3)Rhyolitic volcanism
range). - most viscosity (magma flows least easily)
➢ because of erosion mountains are levelled - gasses escape least easily -> highest P ->
into flatter continental shield areas (land most explosive
inwards) - smallest quantity lava flow -> smallest
➢ During orogenesis rocks are folded making distance flow
forms like anticline folds: syncline folds: - calderas/rhyolitic lava domes
and/or factions (faults and joints). - pyroclastic flows and ash rains
In the collision zone the rocks may be folded Formation of lava dome: very viscous
(folds) or fractured (faults (fault means materials, low gas pressure.
movement)). When a pyroclastic flow mixes with water, a
Mountain belts: uplifted and folded rocks. devastating volcanic mudflow may form:
Continental shields: eroded mountain Lahar.
ranges build in the collision zones of former
orogeny’s more up to more than 550 Ma ago. RIVER EROSION PROCESSES
Creak: Rivers: develop a specific drainage pattern
when flowing through their river basin. Rivers
Volcanism play an important role in the denudation
Basic magma (low SiO2) (weathering) of the landscape. TWO TIPES
Acid magma (high SiO2) OF RIVERS:
(1) Basaltic volcanism (< SiO2) (1) Braided river
(2) Andesitic volcanism (<> SiO2) (2) Meandering river
(3) Rhyolitic volcanism (>SiO2) • Each river system has a typica longitudinal
profile from the upper reach erosion zone to
viscosity explosive quantity volcano
& the lower reach depositional zone. The upper
distance reach has steeper river gradients, the lower
Basaltic low no large, Shield volcano,
long scoria reach show flatter river gradients until the river
Andesitic average average average
(2x)
Stratovolcano,
composite cone
reaches its erosion base.
Rhyolitic high yes small, lahar Water flows on the surface WHEN:
short
• There is more precipitation than evaporation.
(1) Basaltic volcanism • There is more precipitation/water
- low viscosity (magma flows easily) accumulation than soil can infiltrate.
- gasses escape easily >low P > not explosive Water that flows over the surface can erode +
- large quantity lava flow > long distance flow transport sediments.
- shield volcanoes/cinder cones
, The potential amount of sediment that is
transported and the capacity to erode (1) Processes in the erosive zone:
depend on the amount of water or total • V-shaped incision in hard rock
discharge (m3/s) and the slope or gradient • Vertical erosion is dominant over lateral
(m/m) • Valley forming rivers (erosion, incision,
tectonics) increase the adjacent gradients in
River basin can be divided in three zones: landscapes and stimulate denudation.
1. Eroding upper zone (erosive zone) • Denudation: the wearing away of rock by
2. Middle reach (transport zone) means of weathering, erosion, slope
3. Lower reach (accumulation zone) processes and transport.
The erosion base of the river is the sea (no
discharge or gradient exists anymore)
Drainage density is determined by the The end point for the river gradients is the
permeability of the underlying rock. base level: the lowest point until where the
• Poor permeability: more water → high river can erode (most of the time sea-level),
density of channels gradient=zero, all sediments are deposited,
• Good permeability: less water → low forming a delta.
density of channels
Sorting of sediments:
River patterns in the transport- and
depositional zone
The river pattern is determined by
(1) the stream power of water (amount +
gradients)
(2) the amount and type of sediments.
River types: • The specific stream power determines
• Braided rivers: which grainsizes are transported or deposited.
-high stream power • River deposits are layered.
-high peak discharge and or steep gradients • Deposition of sands on the bank of the river:
-transports large amounts of relatively coarse formation of a natural levee.
sediments (sand and gravel). Sediment transport and river deposits
• Meandering rivers: The floodplain or alluvial plain of a
-regular intermediate stream power meandering river with typical geomorphology:
-gentle gradient • Natura levee
-transport less sediments of a more finer o High grounds close to the stream channel,
compositions (clay, silt and sand). coarse sediments
• Backswamp
Braided: o Lower (wetland) areas away from the
• A constantly changing system of numerous stream channel, fine sediments.
shallow stream channels separated by shifting • Point bars
bars of sand and gravels. o Inner bend deposits of meandering loop,
• The high sediment load is often the fining upwards.
consequence of cold, and or dry climates • Old channel belt
where vegetation is limited. o Abandoned part of the river system
including point bars and levees, slightly higher
Meandering: in the
• One single regularly winding deep stream landscape with coarser sediments than in the
channel that gradually changes position by backswamp area.
eroding in the outer river bend and depositing Alluvial fans: A fan shaped braided
in the inner bend of the meander loop. depositional are from a steep gradient
• Gradual location charging meander loops mountain stream that loses its
• Deposits of fine sediments on a in general stream power because of the lower gradients
wetland floodplain. while entering a larger and flatter valley floor.
• The abandoned and cut-of meander loops River terraces
are called oxbow lakes.
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