Date post: | 16-May-2015 |
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New Zealand’s Natural Landscapes
How we got what we have
Outline
• Relief and landforming processes
• Plate Tectonics
• Processes to produce landforms– Faulting– Folding– Volcanism
• Landmodifying processes– Erosion
Relief and landform processes
Plate Tectonics
Theory of Plate Tectonics
• The surface of the earth is covered by crustal plates which collide or are pulled apart from one another (fig 1)
• They are driven by convection currents (fig 2)
Figure 1: Plate tectonics theory says the earth is made up of interlocking crustal plates Figure 2: Beneath the earth’s crust
Plate margins – Where the action is!
• Plate margins are where plates collide, move past, slide past or spread apart
• There are three types of plate margin– Destructive plate margin
• Fig 1
– Constructive plate margin• Fig 2
– Passive plate margin• Fig 3
Figure 1: Destructive plate margin
Figure 2: Constructive plate margin (sea floor spreading)
Figure 3: Passive plate margin
Destructive plate margins
• Where plates move towards each other one is forced under the other, called subduction
• The thinner oceanic plate is forced under the thicker continental plate
Constructive plate margins
• Where plates are moving apart sea-floor spreading occurs
• The magma rises into the cracks between the plates, this causes mid-oceanic ridges
Passive plate margin
• Where the plates are moving past one another it is known as a conservative boundary
• Crustal rock is neither destroyed nor created
Tectonics of NZ
Processes to produce landforms
Faulting
• Faulting is the movement of the crust along zones of weakness– Generally plate margins
• As pressure builds old, brittle rocks break and move in blocks
• The land shifts upwards, downwards or sideways
• The southern Alps of NZ have been uplifted by faulting
Folding
• Folding is the process where sedimentary rock is pushed and squeezed as surrounding hard rock is moved by plate tectonics
• The soft rock bends and twists• This creates more gentle landscapes• The North
Island hill country has been formedby folding
Volcanism• Subducting oceanic rock melts and then
escapes to the surface through a weakness• Typical
volcanic landforms are – lava or ash
erupted from volcanoes
– Calderas, lake Taupo
– Thick deposits of ash, the Volcanic Plateau
– Old lava cones, Auckland volcanic field
Land modifying processes
Erosion
• Once land is formed other processes occur to change or modify the landform
• This wearing down and transportation of the earth’s surface is known as erosion
• This occurs by– Weathering– Transportation– Deposition
Weathering
• The breaking down and wearing away of the land by chemical processes
• Some of the these processes are– Fluvial erosion
• Erosion by running water
– Glacial erosion– Periglacial erosion
• Freeze thaw
– Aeolian erosion– Coastal erosion
Transportation
• Once the material has been broken down by one of the chemical processes it is moved from that place
• Some of the forms of transportation are– Fluvial
• Running water
– Glacial– Aeolian– Coastal
Deposition
• Once the material has been transported it is put somewhere else
• This is known as deposition– It is deposited somewhere
• Example– A river transports material downstream– Where the river is flowing fast it picks up a lot of
material in its flow– As the speed of the river slows it can’t transport all the
material anymore, its not moving fast enough to hold it
– It then deposits that material