World Geog 3200/3202
Ch #1: Major Land & Water Forms
Structure of the Earth
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structure has been defined by studying earthquakes
also known as seismology
Three main parts of the Earth:
a. Crust
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outermost layer
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known as the lithosphere
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estimated to be anywhere from 1-100 km thick
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contains mountains, hills, plains, plateaus, valleys...
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made of minerals and rocks
b. Mantle
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middle region of the Earth
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a thick layer of dense rock and metal oxides
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2900 km thick
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accounts for 82% of the Earth’s volume
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made mostly of perodite which is a type of rock composed
of iron, magnesium, silicon and oxygen
c. Core
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centre of the Earth
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anywhere from 4000-6000 degrees Celsius even though it
has been cooling for over 4.5 billion years
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has two layers called the inner (solid) and outer core
(liquid) made mostly of iron and nickel
Topography:
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the natural and human features of the Earth’s surface
Four common landform features of the Earth:
a. Valleys
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depressions in the Earth’s crust
b. Plains
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a flat region that is frequently found along the coastal areas
or at lower elevations
c. Plateaus
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another type of flat region
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raised upward into a higher elevation by movements of the
Earth’s crust
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found in the interior of continents or between mountain
ranges
d. Mountains and Hills
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highest relief landforms on Earth’s surface
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hills have a height of less than 300m...usually isolated and
made up of rock piles and soil left behind by glacial erosion
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mountains have an elevation greater than 300m
occur in long linear chains on the margins of continents
rock layers are badly deformed as a result of strong forces
in and below the Earth
Importance of PLATE TECTONICS:
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volcanic activity broke the Earth’s crust into tectonic plates
that carry the continents and oceans with them
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tectonic plates float on a sea of hot soft rock called magma
found in the asthenosphere
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the plates are constantly moving due to convection currents
which are formed when magma near the core heats then
rises towards the surface as its density decreases
Compressional Forces:
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occur when tectonic plates move towards each other
causing the rock layers to bend, warp and push upward
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commonly called folding
Tensional Forces:
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occur when tectonic plates move away from each other,
pulling apart the Earth’s crust until it is stretched to the
point where it cracks
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commonly called faulting
Anticline and Synclines
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when folding occurs with the layers of the earth two simple
structures are formed:
a. Anticlines
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higher areas or peaks (upfold)
b. Synclines
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lower valley areas or troughs (downfold)
A
B
Z
B
A
Compressional forces create fold mountains:
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most mountains are found on the edges of continents
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continental plates lie next to oceanic plates
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rock layers between these two plates are squeezed upwards
making a mountain
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the process of bending, buckling and pushing is called
folding
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Andes Mountains were formed when the South American
plate collided with the Nazca plate
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Rocky Mountains were formed when the North American
plate collided with the Pacific plate
Explain how tensional forces create a normal fault:
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when plates are compressed against each other it results in
enormous pressure
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the rock layers become brittle, fracture and break into a
fault
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results in great blocks of the Earth’s crust being pushed up
or dropped down
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if a plate on one side drops down lower than the plate on
the other side, then it results in a normal fault
Two other types of faults:
a. Reverse Fault
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simple rock layers around a fault push against each other
resulting in one block being pushed up over the other
b. Overthrust Fault
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when the plate that suffers the fault has already undergone
folding and its folded layers are pushed up and thrust over
layers on the fault’s other side
Explain what causes a volcano to erupt:
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a volcano is triggered by heat
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the plate boundaries are very hot because of friction,
pressure and decay of radioactive materials
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this heat melts the rock beneath the crust making magma
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magma forms in underground pockets and flows into cracks
and fractures of crustal rock
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the molten rock reaches the surface through a vent
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an eruption contains:
a. lava - liquid rock
b. ash - small molten rock fragments
c. cinders - fine grained molten fragments
d. gases - carbon dioxide, hydrogen, nitrogen...
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mild volcanic eruptions have thin liquidy lava with small
amounts of gas
explosive eruptions have thick lava flows with large
quantities of gas, ash and cinders
Three types of volcanic cones:
a. Ash and Cinder
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symmetrical shape
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steep sides
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large crater
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results from explosive volcanic eruptions consisting of ash
and cinder with slow flowing rapidly hardening lava
b. Shield Cones
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broad and flat
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gently sloping sides
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results from mild explosions with little ash and very thin
liquid lava
c. Composite Cones
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have an intermediate height and steepness
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develops from alternate periods of violent eruptions and
relatively quiet activities
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sides are made from ash, cinder and lava
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weak structure that allows lava to seep through the cracks
forming smaller cones