Topography: the natural and human features of Earth's surface
Hills & mountains
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Hills are smaller, generally have a height of less than 300 m, usually isolated features
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Mountains (300 m +) usually occur in chains (ranges) most often along the edges of continents
Plains & Plateaus
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Plains are flat regions frequently found along coastal areas or other low elevations
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Plateaus are flat regions that have been raised to higher elevations by movements of the
earth’s crust
The earth’s surface is partly shaped by “build-up” forces resulting from tectonic activity.
Essentially, the earth’s crust (lithosphere) is divided into twenty tectonic plates that float around on an
underground sea of molten rock.
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Convectional currents in the melted rock (magma) cause the plates to move.
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We (North America) are moving away from Europe by a few cm every year.
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Sometimes the plates converge or come together and push against each other causing
compressional force.
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Sometimes the plates diverge or pull apart causing tensional force
Plate tectonics: The main features are:
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The Earth's surface is made up of a series of large plates (like pieces of a giant jigsaw puzzle).
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Convection currents beneath the plates move the plates in different directions.
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The source of heat driving the convection currents is radioactive decay which is happening deep
in the Earth.
Mountains are one of the earth’s main landforms and are formed by THREE main processes:
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Faulting
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Folding
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Volcanic Activity
Fault Mountains (rock layers break or fracture)
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These mountains form when faults or cracks in the earth's crust force some materials or blocks
of rock up, and others down.
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Instead of the earth folding over, the earth's crust fractures (pulls apart).
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It breaks into blocks of rock which move up and down, as they move apart and blocks of rock
end up being stacked on one another.
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A fault is a large crack in the Earth's crust where one part of the crust has moved against
another part.
Normal faults form when the hanging wall drops down.
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The forces that create normal faults are tensional.
Reverse faults form when the hanging wall moves up.
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The forces creating reverse faults are compressional
Overthrust Fault
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A geological fault in which the upper side appears to have been pushed upward by compression
Block Mountain Fault
Rift Valley Fault
A graben is a depressed block of land bordered by parallel faults
Volcanic Mountains
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Volcanic Mountains are formed when molten rock (magma) deep within the earth, erupts, and
piles upon the surface.
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When the ash and lava cools, it builds a cone of rock. Rock and lava pile up, layer on top of layer.
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To understand what causes volcanoes, you need to understand how the earth is made up.
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The earth has three main layers: the crust, the mantle and the core.
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The crust is made up of solid rock and varies in thickness. It is more than 60km thick under
mountain chains like the Alps and Himalayas, but just 5km under the oceans.
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The mantle is a thick layer of molten rock (called magma), and the core is made up of an outer
liquid layer and a solid centre.
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Temperatures inside the earth are very high – over 5000° C in the core.
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the planet on which we live is a huge fiery ball of hot molten rock, surrounded by a few
kilometers of relatively cool, hard rock – the crust.
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Because heat rises, the magma in the earth’s mantle has to find a way to rise upwards though
the crust above it, rather like the way that hot air rises.
An Erupting Volcano
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A volcano erupts when magma escapes from inside the earth.
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As the magma is escaping from a confined space, a lot of energy is released with it, as happens
with any other explosion.
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This is why many eruptions also produce huge quantities of gases and dust.
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Magma sometimes rises under enormous pressure, so it not only finds cracks in the earth’s
crust, it can also create them.
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When magma reaches the earth’s surface it is called lava.
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The nature of every volcano is determined by its eruptive styles, which are themselves
determined by the kind of magma rising to the surface.
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The possible combinations of eruptive styles and resulting landscape forms is complex
3 Types of Volcanoes
1. Ash and cinder cones:
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Formed when ash and cinder are violently spewed out form an erupting volcano and blown to
great heights.
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This type of volcano is hardly composed of any lava, most cinder and ash.
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The ash and cinder cone volcano normally have steep sides and a small crater (e.g. Mount
Paricutin in Mexico)
2. Composite Volcano
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Formed by alternating levels of lava, ash and cinder.
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Eruptions are not as violent as the ash and cinder cones, as lava also escapes from many side
vents.
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Composite volcanoes are high and have gentle slopes at the base but steeper slopes near the
top. (e.g. Mount Vesuvius, Italy)
3. Shield Volcano:
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Forms when eruptions produce runny lava that flows across a vast area instead of making a
cone.
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Shield volcanoes usually have many side vents.
NOTE:
Majority of volcanic eruptions occur near plate boundaries!
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Convergent Plate movement: Most powerful eruptions occur when plates collide, where there
is an enormous amount of energy built up in the Earth’s crust .
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Divergent Plate movement: Volcanoes can also erupt when plates move apart from each
other, but these eruptions are much gentler.