2. 3. INTERNAL FORCES OF RELIEF.
A. THEORY OF CONTINENTAL DRIFT:
Many million years ago there was only a single super-continent, called
Pangaea, which broke up into fragments to make the continents we have
today.
Look at the coasts of the current continents, we can see that they seem
to match like an enormous jigsaw.
4. B) TECTONIC PLATES:
The Earth’s crust is not just one big piece of rock. It is divided into smaller pieces of
crust called tectonic plates.
The plates move because the mantle underneath them is moving, but they only
move very slowly.
The places where the plates meet are called plate boundaries or plate margins.
5. C) WHAT HAPPENS WHEN THE PLATES MOVE?
FAULTS AND FOLDS:
Below the surface of the Earth, gases and compressed materials put
pressure on the crust. They can deform it or make it crack. They are
called INTERNAL FORCES.
The Earth’s surface ondulates or fractures by the pressure from molten
materials in the mantle.
When Earth’s surface ondulates FOLDS are created.
When the surface is extremely ridig FAULTS are
created, and one block rise while the other sink.
6. Fold:
• When two plates move towards each other the Earth’s surface is forced
upwards or folded.
• This happens very slowly.
7. Faults:
• When the plates againts each other, pressure can build up. Sometimes
this causes the rock to split, making a fault in the rock.
• On one side of the fault, the ground rises, and on the other side it falls.
8. The Earth’s crust:
It is thicker where it forms the continents and thinner where the oceans cover
it.
The crust is not smooth, there are features of land relief (mountains,
valleys, basins or depressions and plains) on land and under the sea.
The Earth’s relief is constantly changing because of internal and external
forces.
The Earth’s relief:
Eath’s Surface is not flat and smooth.
Relief (relieve) consists of all the features, such as mountains and valleys,
which make the terrain around us so varied.
Landforms (accidentes geográficos): is another way to name all these
features.
Remember:
9. 5.HOW DOES RELIEF CHANGE?
o The Earth’ relief is shaped by its internal forces: pressures (the
movement of tectonic plates: folds and faults), volcanoes and
earthquakes.
o Relief is also shaped by external agents on the Earth’s surface
(external forces): water, wind, changes of temperature and living
things (human action).
o All of these external agents modify relief by three processes:
Erosion: materials, such as rocks and soil, are broken up and moved
around by external agents.
Transportation: these materials are then transported by seas, rivers,
ice or wind.
Deposition: eroded rocks, sand and mud are deposited in low areas
where the sediments acumulate.
10. EXTERNAL FORCES OF RELIEF
o Water: plays a very important role in erosion, transport and deposition (rivers,
seas and oceans, rain water and ground water).
11. EXTERNAL FORCES OF RELIEF
o Wind: (aeolian erosion)
Is when wind erodes and transports rocks and sand.
It often occurs in dry climates, sucha as deserts, because there is little
vegetation to protect the soil.
o Changes of temperature:
In deserts or mountainous areas it is much hotter during the day than at
night-time.
Water sometimes enter the cracks in rocks. It may break the rocks if it
freezes and expands.
o Living things:
Vegetation or animals.
Human action: through activities such as agriculture, deforestaion or mining.
Roads or reservoirs are man-made features of the Earth’s relief.
