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