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Surface processes
Bilingual biology and geology 3º ESO
Mª Eugenia Alba Torreiro
How the Earth’s surface changes
Exogenous geological process:
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The Earth’s surface is continually
being changed and shaped by
different exogenous geological
agents as temperature, humidity,
wind, precipitation, streams and
rivers, ice, seas, etc.
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When these agents work on rocks
of the Earth’s surface they carry
out what are called exogenous
geological processes:
Erosion
Transportation
Sedimentation (deposition)
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Erosion, Transportation, Sedimentation.
Exogenous geological processes
Weathering
Weathering is the processes of fragmentation and alteration of rocks by the
joint action of the atmosphere, water and living things.
The weathering take place in two ways:
Physical weathering takes place when solid rocks are fragmented by physical
processes that do not change its chemical composition.
Chemical weathering takes place when minerals in rocks are chemically
altered or dissolved.
SOIL
When rocks on the Earth’s surface are weathered, they eventually produce
soil. Soil formation is a very slow process which can last thousands of years.
Types of weathering
Soil
Streams and rivers
Torrents
Permanent streams and rivers
They are continuous currents of water which run along a fixed channel in a valley. They are formed by
rainwater, springs or melting ice and have three stages: upper course, middle course and lower course.
The stages of the rivers
Upper course
• The river is closest to its source.
• It usually runs down a steep slope and the water flows quickly.
• There is a lot of erosion and little sedimentation.
• The river valley is often narrow and V-shaped with frequent rapids and waterfalls.
• Gorges and canyons are features of this stage.
Middle course
Middle course
• The slope is much shallower.
• The water flows more slowly: heavier
materials are deposited but erosion and
transportation of lighter materials continues.
Their features are:
• V-shaped river valley but the slopes are less
steep and the bottom is flat. The deposited
sediment creates floodplains.
• Meandres which are large bends in the river
on flat terrain.
• Fluvial terraces which are the remains of old
floodplains when the river flowed at a higher
elevation
Lower course
• It is the last stage of the river.
• The slope is minimal and the water flows slowly.
• Meanders are large and the river valley is very wide with large floodplains.
• Materials are deposited as sediments.
• In the river mouth, the accumulation of sediment forms deltas.
• If the deltas are washes away an estuary is formed.
Karst topography
• Karst is a landscape
where the rocks on the
Earth’s surface, usually
limestone or dolomite,
has been dissolved by
groundwater, forming an
irregular surface.
Karst topography
Surface features
• Limestone pavements, flat
surfaces crossed by many
fissures.
• Sinkholes, depressions in
the ground.
• Canyons, deep channels
with vertical walls.
Underground features
• Caves, tunnels and galleries
in the rock.
• Stalactites, pointed
columns descending from
the roof.
• Stalagmites, pointed
columns ascending from the
floor.
• Columns, when a stalactite
and stalagmite join
together.
The sea
Action of waves. Waves break off fragments of rock and
throw them against the coast as projectiles, increasing
the erosive power of the water. This process is known
marine abrasion.
Action of tides. The rise and fall of the sea level is
capable of transporting abundant loose materials.
Action of currents. Coastal currents, which run
parallel to the coast, are capable of transporting
large amounts of sand and small stones.
Erosive coastal features
Rocky coasts
Cliffs, high and rough walls of rock formed by marine
erosion due to waves breaking at their feet.
Abrasion platform, a flat area at the bottom of cliffs
formed by erosion of the cliffs.
Caves, natural arches and stacks, are the result of different rocks which have different resistance to erosion.
Transportation and sedimentary coastal features
Beach
Marshes
Sand bank
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Beaches are formed by the accumulation of gravel and sand on the shore.
Barrier island are deposits of sand (sandbank) parallel to the coast.
Tombolos are sand banks or spits which attach small island to the coast.
Sand spits are long deposits of sands and gravels attached to the coast and formed by the longshore drift.
Lagoons are areas of water formed when sandbanks close off a bay or a gulf.
Marshes are a kind of wetland formed at the mouths of rivers by the action of the tides.
Flat-coasts
Sand bank and spit
Beach
Tombolo
Marshes
Glaciers
A glacier is an enormous mass of permanent ice that forms in cold regions. It moves slowly downhill, with strong erosive power,
shaping the landscape.
There are two types of glaciers: ice sheets or polar glaciers and valley glaciers.
The two types of glaciers
Alpine glacier
Ice sheet
Antarctica
14 million km2
30 million km3 of ice
Greenland
1,7 million km2
2 million km3 of ice
An ice sheet is a mass that covers more than 50 000 km2 of land area.
The cirque
• The accumulation zone is the highest part of the
glacier.
• The snow accumulates, is compacted and slowly
transforms into ice.
• The glacier erodes the land into an amphitheatreshaped valley called cirque.
Tarn (lake)
It is a mountain lake formed in the cirque when the ice
melts.
The tongue
The slipping zone includes one or more tongues of ice which
slide slowly downhill creating a U-shaped valley. The materials
eroded and transported by the ice forms deposits called
moraines.
The glacier terminus is the bottom of the glacier.
Here, the ice breaks and melts and deposits the
transported materials. These materials form
terminal moraines.
The wind
The action of the wind is predominant in arid regions where precipitation is low and vegetation almost nonexistent: deserts, semi deserts and beaches.
Natural arch
Alveolar erostion
Deflation. The removal of
loose materials from the
ground.
Dunes