Movers and Shakers: How Landforms are Created

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Movers and Shakers How Landforms are Created

• Chapter 5

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Landform Types

• There are six different types of landforms on
  earths surface that were formed by plate
  tectonics.
• Mountains
• Highlands
• Plateau
• Hills
• Plains
• Valley

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Defining Landform Types

• Elevation
• Height above sea level
• Mountains have the highest elevation and valleys
  have the lowest
• Surface Relief
• Refers to the surface of the feature
• Flat surfaces have low relief
• Rough, hilly and jagged surfaces have high relief

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Mountains

• Rugged peaks of varying heights
• High elevation and relief
• Formed by tectonic folding, faulting and
  volcanism

Highlands

• Like mountains but all the peaks are the same
  height
• High elevation and relief
• Formed by isostatic uplift followed by millions
  of years of erosion.

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Plateau

• High, flat table of land
• High elevation and low relief
• Formed by isostatic uplift often extrusive
  former lava flow

Hills

• Rounded mounds of no particular shape
• Medium relief and elevation
• Either old worn down mountains or depositional
  features

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Plains

• Low flat land
• Low elevation and relief
• Formed from a former uplifted sea floor, or
  deposited material from mountain erosion

Valley

• Low flat land surrounded by hills or mountains
• Low elevation and relief
• Formed from folding, faulting or erosion.

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Landforms Created Through Isostatic Movement

• Isostasy slowly elevates the land and creates new
  landforms
• Isostatic rebound occurs when you have something
  very heavy (like a glacier) pushing down on the
  earths crust.
• When the weight is removed the crust very slowly
  bounces back.
• This is one of the main reasons why fossil fuels
  are found so close to the surface.

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Mountain Building

• Mountain building is also known as orogny.
• It is a process that takes hundreds of millions
  of years
• Formed in three ways
• Folding
• Faulting
• Volcanism

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Landforms Created Through Folding

• Folding occurs when the earths crust is pushed
  up from either or both sides.
• Fold Mountains form as plates slide into each
  other and the crust is pushed up.
• Found near the leading edge of plates
• Older fold mountains are often so worn down that
  they look like hills
• You can tell a mountain has been folded because
  the rock layers run up and down in parallel bands

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Landforms Created Through Folding

• Its hard to identify fold mountains for two
  reasons
• Erosion often wears away some of the folded
  layers.
• Folding often occurs along with faulting and
  volcanism

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Landforms Created Through Folding

• The structure of a fold mountain can be complex.
• Simple ones are made up of layers that rise and
  fall like waves of water.
• The peaks are called anticlines
• The troughs or valleys are called synclines

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Landforms Created Through Faulting

• Faulting occurs when blocks of rock fracture or
  pull apart
• The mid-oceanic ridge is a perfect example
• Two plates have pulled away from each other
• Faulting can occur very quickly (seconds or
  minutes) where as folding occurs over thousands
  and millions of years.

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Landforms Created Through Faulting

• Faults occur wherever a plate experiences tension
  or compression
• Tension pulling apart of plates
• Compression when plates are rammed together

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There are many different landforms that faulting
creates.

• Subduction Fault
• when an oceanic plate moves under a continental
  plate.
• Run along continental borders
• Deep underwater trenches
• Coast line is mountainous
• Extension Fault
• When two plates are pulling away from each other
• Example mid-oceanic ridge, the crust is so thin
  here that magma oozes up into the fault lines and
  hardness into new crust.

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There are many different landforms that faulting
creates.

• Rift Valleys or Grabens
• form when there are two parallel faults
• The land between the faults sinks as they pull
  apart
• Example great rift valley in Africa
• Horst or Block Mountain
• Forms when land rises between parallel faults
• Example Grand Tetons in U.S.A.

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There are many different landforms that faulting
creates.

• Collision Fault
• Forms when two plates crash into one another
• One plate slides up relative to the other
  creating a fault plane
• Basically the same as the subduction fault but
  the two plates are continental
• There is no subduction in this case because the
  plates are the same thickness and density.
• They plow into each other like two cars crashing.
• Example The Himalayan Mountains

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There are many different landforms that faulting
creates.

• Strike-Slip Fault
• Occur when two plates slide laterally past one
  another
• Example San Andrea Fault in California

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Landforms Created Through Volcanism

• Volcanoes are examples of extrusive volcanism
• Extrusive means that the feature is visible on
  the surface of the earth
• Under the surface magma flows into cracks within
  the crust.
• This is intrusive because it is happening under
  the surface.

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Landforms Created Through Volcanism

• Magma often accumulates in a magma chamber.
• If the pressure is great enough and there are
  fault lines to facilitate movement the magma
  flows onto the surface through a magma conduit
• Sometimes the magma solidifies before it has a
  chance to flow out of the volcano, and a magma
  plug is formed.

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Main Features of a Volcano
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Landforms Created Through Volcanism

• Vesuvian Volcanoes
• Volcanoes that have had a magma plug.
• The plug lets the pressure build up more and more
  until there is a violent eruption of lava, ash
  and rocks
• Hawaiian Volcanoes
• Less violent
• Form over a hot spot
• Less viscous lava so it flows
  more freely and
  doesnt
  form a plug

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Landforms Created Through Volcanism

• Intrusions
• When magma is forced into small cracks in the
  crust you get
• Dikes, sills and laccoliths
• When magma is forced into a large opening inside
  the crust you get
• Batholiths (100s of kms across)

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Landforms Created Through Volcanism