Tectonics and Volcanoes

Question 1

Where is oceanic and continental crust located in NZ?

Answer 1

• Oceanic crust is located in the cool-colored sea-bed.
• Land and the red/orange-toned sea-bed is the continental crust.

Question 2

Describe how tectonic interaction caused the Kermadec Trench.

Answer 2

• Formed by the Pacific Plate subducting under the Australian Plate.
• Both plates are oceanic crust, so the PP drags the AP down, forming a deep ocean trench.
• AP stretches

Question 3

Describe how tectonic interaction caused the Hikurangi Trough.

Answer 3

• Formed by the denser oceanic crust of the PP subducting under the more buoyant continental crust of AP.
• PP drags the AP down forming a moderately deep trough.

Question 4

Describe how tectonic interaction caused the Puyseger Trench.

Answer 4

• Formed by the denser oceanic crust of the AP subducting under the less dense oceanic crust of the PP.
• AP drags down the PP (both oceanic) forming a deep ocean trench. –> not as deep as Kermadec.

Question 5

Describe how tectonic interaction caused the Kermadec Volcanoes.

Answer 5

Formed by the denser and older oceanic crust of the PP subducting under the less dense oceanic crust of the AP (overriding plate).

Question 6

Describe how tectonic interaction caused the Taupo volcanic zone and Taranki.

Answer 6

Formed by the denser ocenaic crust of PP subducting under the more buoyant continental crust of AP.

Question 7

What happens when the Pacific Plate reaches a certain depth?

Answer 7

When the PP reaches a certain depth (about 20km) magma forms with the help of superheated water from wet sediments. This is why the TVZ and Kermadec volcanoes are parallel to the tectonic boundary.

Question 8

Describe how tectonic interaction caused the Auckland volcanoes.

Answer 8

• Formed because the AP is being stretched in that area.
• Occasionally causes a stretching/cracking of the crust, allowing molten magma from 100 km deep in the mantle to start rising.
• Forming an Auckland volcano.

Question 9

Describe how tectonic interaction caused the Mountain building and the Southern Alps.

Answer 9

• Axial ranges such as Rimutaka Ranges at start of Wellington and go north - parallel to the tectonic boundary
• They run parallel to major faults that relieve tension caused by the tectonic plate boundary.
• Blocks of land rise and are eroded forming the ranges.

Question 10

Describe how tectonic interaction caused the Southern Alps.

Answer 10

• They form in the South Island continental crust of both the PP and AP colliding.
• PP overrides AP (both are buoyant continental crust) uplifting the land and forming the Southern Alps.
• SA are eroding because of high rainfall in West Coast
• Uplift plus erosion means SA will remain at same height.

Question 11

What is a volcano?

Answer 11

A volcano is a vent that erupts and deposits lava around the volcano. Magma rises from deep underground and erupts when the surface above is weakened by the magma’s pressure.

Question 12

Where does the magma come from?

Answer 12

Magma generally pools in a magma chamber beneath the volcano before eruption.

Question 13

What is magma?

Answer 13

Magma is molten rock rising from deep beneath the ground. Can erupt gently or explosively. The temp varies from 650 C to 1200 C.

Question 14

What does a magma’s erupt agression depend on?

Answer 14

• Amount of silica. More silica means the magma becomes more viscous. Meaning the magma can trap more gas.
• Amount of silica can also depend on the amount of sediment subducted and/or the depth of the continental crust the magma travels through to get to the surface.

Question 15

What are the types of magma?

Answer 15

• Basaltic
• Andesitic
• Rhyoditic

Question 16

Describe what happens when volcanic ash occurs.

Answer 16

• The ash has gone into the troposphere and spreading out.
• Small eruption –> will effect weather briefly
• Large eruption –> Will stay up in the stratosphere for longer, can affect the weather for a few years.
• WILL NOT cause long-term climate change.

Question 17

Descrip what happens when pyroclastic flows and crater collapses occur.

Answer 17

• Can cause tsunamis if they happen near/under the ocean.
• Flows can travel very fast.
• Size of flow depends on size/violence of the eruption.
• Dmg can be extensive, especially if they occur near towns/cities.

Question 18

What is volcanic gas?

Answer 18

• Consists of carbon dioxide, water vapour, and sulphur dioxide. TOXIC
• Carbon dioxide –> melted carbonate rocks (limestone), consists of plankton skeletons.
• Gas bubbles expand when rising in magma –> expansion of now frothy magma puting pressure underneath surface.

Question 19

Name and describe the different types of explosions.

Answer 19

• Magmatic - caused by bubbles of gas in the magma, the more gas there is the more explosive the eruption. (Ngauruhoe)
• Phreatomagmatic - Caused by hot magma coming up under a water source (lake). Liquid water flashes to vapour –> expands rapidly.

Question 20

Name the types of tephra (ash).

Answer 20

• Volcanic bomb
• Ash
• Cinders

Question 21

How do subduction volcanoes form?

Answer 21

• TVZ, Mt. Taranaki, and Kermadec volcanoes
• Formed when PP subducts under AP off the coast of the North Island and along Kermadec Trench
• Rising magma forces its way up through vents when PP reaches certain depth.
• Parallel to tectonic plate boundary

Question 22

How does magma form in subduction volcanoes?

Answer 22

• Water laden sediments and limestone from the bottom become subducted
• PP reaches depth and the water becomes superheated– lowering melting point of the overriding AP rock, melting it
• Melted rock forms magma. Hot so less dense. Chaos ensues