Tectonics Pack A

Question 1

How do plates move by internal heating within the Earth?

Answer 1

• Heat from the core is moved towards the surface by convection currents in the mantle
• These spread out at the surfaces carrying plates with them
• Plates move on the asthenosphere

Question 2

How do plates move by ridge push?

Answer 2

• Molten magma rises at a mid ocean ridge divergent boundary
• Rocks in the lithosphere are heated, expand and rise above the surrounding sea floor
• This forms a steep slope away from the ridge
• As the rock cools it becomes denser and gravity causes it to slide down the ridge
• This exerts a force on the plates
• Gravitational sliding is the active driving force

Question 3

How do plates move by slab pull?

Answer 3

• At most convergent boundaries, one plate is denser/heavier than the other
• The denser plate subducts beneath the less dense plate
• The subduing plate is colder/ heavier than the mantle so it continues to sink pulling the rest of the plate with it

Question 4

How are plates distributed?

Answer 4

Lithosphere is divided into seven large and three smaller plates

Question 5

What happens at a divergent plate margin?

Answer 5

• Plates are moving apart from one another
• Magma from the mantle rises up to construct a new crust
• This causes earthquakes and shield volcanoes

Question 6

What landforms are found at divergent plate boundaries?

Answer 6

• Ocean ridges (e.g. Mid-Atlantic Ridge)
• Rift valleys (e.g. East African Rift Valley)
• Shield volcanoes
• Lava tubes and geysers

Question 7

What happens at a convergent destructive plate boundary?

Answer 7

• Plate are moving towards each other
• Usually involves an oceanic and continental plate
• Oceanic plate is forced beneath the continental plate (subduction) as it is denser
• This forms an ocean trench
• The plate sink into the magma and melts to form magma
• Pressure builds up and magama escapes through weaknesses int the rock

Question 8

What landforms and hazards are found at convergent destructive plate boundaries?

Answer 8

• Composite volcano
• Earthquakes
• Ocean trench

Question 9

What happens at a convergent collision boundary?

Answer 9

• Two continental plates collide and neither can sink
• Land buckles upwards to form fold mountains

Question 10

What landforms and hazards are found at a convergent collision plate boundary?

Answer 10

• Super volcanoes (e.g. Campi Flegrei)
• ## Cinder cones (e.g. Paricutin, Mexico)

Question 11

What happens at a transform (conservative) plate boundary?

Answer 11

• Plates slide past each other in opposite directions or in same direction at different speeds
• Friction occurs and plates become stuck
• Pressure builds up and is released to form an earthquake
• Can be destructive as close to Earth’s surface

Question 12

What hazards occur at a transform (conservative) boundary?

Answer 12

• Earthquakes
• Fault lines (e.g. San Andreas)

Question 13

What layers is the Earth divided into?

Answer 13

• Crust
• Mantle
• Core

Question 14

What is the lithosphere?

Answer 14

• Outer solid part of the Earth (including crust and upper mantle)
• 100km thick but thickness is age dependent

Question 15

What is the asthenosphere?

Answer 15

• The ductile part of the earth just below the lithosphere (including the upper mantle)
• 180km thick

Question 16

What is the Moho Discontinuity?

Answer 16

• Boundary between the crust and mantle
• Depth where seismic waves change velocity and there is a change in chemical composition
• 60 to 80 km deep beneath continents and between 5 to 8 km deep beneath ocean floor

Question 17

What are the properties of the inner core?

Answer 17

• 5000 to 6000°C
• Solid due to the pressure
• Iron and nickel
• 1250km radius

Question 18

What are the properties of the outer core?

Answer 18

• 4000 to 6000°C
• Liquid
• Iron, nickel, sulfur and oxygen
• 2250km thick

Question 19

What are the properties of the lower mantle?

Answer 19

• 3000 to 4000°C
• Solid due to pressure
• Iron, oxygen, silicon, magnesium and aluminium
• Found between 670km and 2890km below surface

Question 20

What are the properties of the upper mantle?

Answer 20

• 1400 to 3000°C
• Liquid/solid as lower part of is solid and melted rock but upper region is stiffer as it’s cooler
• Iron, oxygen, silicon, magnesium and aluminium
• Up to 670km below Earth’s surface
• Upper part is known as the asthenosphere

Question 21

What are the properties of the crust?

Answer 21

• 22°C
• Solid
• Oceanic crust = iron, oxygen, silicon, magnesium, aluminium
• Continental crust = granite, sedimentary and metamorphic rocks
• Land is made of continental crust that is 8 to 70km deep (made of sial)
• Ocean bed is made of oceanic crust which is 8km thick (made of rock called basalt)