External geological agents sheila
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Transcript of External geological agents sheila
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External Geological Agents1. WIND: can cause erosion, mass wasting and sedimentation The main erosion processes cause by wind are:
DEFLATION forms a layer of rocks that is called a desert pavement (stony field - reg).
ABRASION forms mushroom-shaped rocks
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Aeolic sedimentation when wind finds an obstacle in the landscape
Sand dunes are formed (in sandy deserts (ergs))
Differents types of dunes: Barchan dunes
Star dunes
Transverse dunes
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2. GLACIERS: are divided into an accumulation zone and an ablation (wastage) zone along an equilibrium line. Glaciers are made up ice and snow, water, rocks and sediments. A glacier moves very slowly (few centimeters to a few meters each day).
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• There are different types of glaciers:Alpine glaciers: cirques, horns, arete , U-valley, moraines (lateral, medial,
end)
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Continental glaciers: which are continuous masses of ice that are much larger than alpine glaciers. Small continental glaciers are called ice fields. Big continental glaciers are called ice sheets.
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3. Wild water:
GREAT AMOUNT OF WATER
STREAMSSTREAMS ARE NON DEFINED NOR PERMANENT COURSES OF WATER
RAINSTORM MODIFY THE RELIEF
Smooth and homogeneous
SOIL
easily eroded
Heterogeneous SOIL
some parts are harder to erode
FAIRIES’ CHIMNEYS
RILL
GULLY
TORRENTS Intermittent , short water courses very steep slopesfixed channelice melts or a period of heavy rains.
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• 4. RIVERS: • 0.0001% of the Earth's water . • Different sources: lakes , springs (from underground), rain or melting snow
and ice (high mountains)
To narrow river consider its drainage basin and its floodplain:drainage basin flood plain
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Rivers (masswasting processes)
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1.Early maturity V-shape valley
2. Late maturity. Flat-floored valley .Narrow flood plain. River begins to meander. Flood plain widens
3. Old age. Very wide flood plain. Cut-off meanders (ox-bow lakes)
Rivers (erosion) three valley shape.
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• 5. Ground water• Groundwater : water in the ground is stored in the spaces between rock particles. • A groundwater aquifer is an underground layer that holds water within soil,
porous rock, or similar material. • A groundwater well may be used to extract water from a groundwater aquifer.
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• Karst relieves are landscapes shaped by the dissolution of a soluble bedrock layer, (usually carbonate rock such as limestone or dolomite) by a mildly acidic water.
• These landscapes display different:• surface landforms (sinkholes, dolines, disappearing and reappearing streams,
poljes) • underground features (extensive caves and cavern systems may be formed. In
caves, the deposition of calicium carbonate may form stalactites, stalagmites, column)
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SEA WATER
waves, tides, sea currents
erosion, transport, sedimentation processes
is constantly movinghas a lot of energy
•6. Sea water in coastal areas
THEY MODEL COASTAL AREAS
WAVES
Chemical Physical weathering
Erosion
Salty sea reacts in chemical ways with rocks and makes them weaker
Stones, other sediments are carried by waves and they crash into the coastal rocks.
Cliffs, sea caves, arches, abrasion platforms, sea stacks
LANDFORMS
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WAVESTransport and sedimentation of materials
Beach: deposition of sand and gravel along the shoreline
Longshore drift: This process is when individual particles are moved along the beach in a zig-zag pattern
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Longshore drift Spits, bay barrier, barrier island, tombolos, lagoons…LANFORMS
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The sediments (sand, mud and pebbles) accumulate in sedimentary basins , forming layers or plies.
These layers of sediment are sinking deeper and deeper into the basins.
Under conditions of high temperatures and high pressures
The sediments become rock (lithified) through a process called DIAGENESIS (it may take millions of years)
SEDIMENTARY ROCKS
Clastic sedimentary rocks such as conglomerate, sandstones, shale .Chemical sedimentary rocks, such us halite, gypsum Organic sedimentary rocks such us limestone, coal.
Types of sedimentary rocks
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CONGLOMERATE SANDSTONE SHALE
HALITE
COALLIMESTONE
GYPSUM