Plate Tectonics

Question 1

What is the inner core of the earth?

Answer 1

It is a solid ball of iron

Question 2

Why is the inner core very hot?

Answer 2

The inner core is very hot due to pressure and radioactive decay (the inner core contains elements such as uranium that give off heat when they decompose).

Question 3

What is the heat from pressure and radioactive decay responsible for?

Answer 3

The heat from pressure and radioactive decay is responsible for the Earth’s internal energy which spreads throughout the structure of the earth.

Question 4

What is the Asthenosphere?

Answer 4

The asthenosphere is a semi-molten layer that constantly moves due to flows of heat called convection currents.

It is below the lithosphere.

Question 5

What is the Mantle?

Answer 5

The Mantle consists of mainly solid rock, and rocks that are high in silicon. However, the very top layer of the mantle is semi-molten magma (the asthenosphere).

Question 6

What is the Lithosphere?

Answer 6

The Earth’s lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic plates.

Question 7

What is the Crust?

Answer 7

The thin top layer of the lithosphere.

Question 8

What are the characteristics of Oceanic crust?

Answer 8

Oceanic Crust is DENSE and DESTROYED by plate movement.

Question 9

What are the characteristics of Continental crust.

Answer 9

Continental crust is less dense that oceanic crust and is not destroyed by plate movement

Question 10

Explain the process of a continental and an ocean plate colliding (Destructive)

1. Subducts
2. ocean trench
3. Fold mountains
4. Asthenosphere
5. pressure
6. Pressurised magma
7. Composite volcanoes, Explosive pressure.

Answer 10

1. The denser and heavier oceanic plate subducts below the continental plate.
2. The plate subducting leaves a deep ocean trench (e.g. Mariana Trench in Western Pacific Ocean).
3. Fold mountains occur when sediment is pushed upwards during subduction.

4.The oceanic crust is melted as it subducts into the asthenosphere.

5. The extra magma created causes pressure to build up
6. Pressurised magma is forced through the weak areas of the continental plate.
7. Explosive, high pressure volcanoes erupt through the continental plate, known as composite volcanoes.

Question 11

What are Volcanic island arcs?

(Description for 8 marker)

Answer 11

Volcanic arcs are a type of archipelago of volcanic islands close two a boundary between to converging tectonic plates.

Question 12

What is an Ocean trench?

(Description for 8 marker)

Answer 12

Ocean trenches are large scale features that are long and relatively narrow depressions in the ocean floor.

-the asymmetric V-shaped oceanic trenches stretch 30-60miles.

Question 13

What is the process of sea floor spreading?

(Description for 8 marker).

Answer 13

Sea floor spreading is a process which occurs at mid ocean ridges where new ocean floor (basaltic magma) is formed through volcanic activity, this ocean floor gradually moves away from the ridge.

Question 14

What are fold mountains?

Answer 14

Fold mountains are large mountain ranges (E.g. Andes, Himalaya, Alps and Rockies mountains). For example, The Himalayas were created from shallow sea bed sediments under the Tethys sea, which have been pushed up and folded as a result of the Indo-Australian plate moving into the Eurasian plate).

Question 15

Explain how fold mountains are formed?

1. Sediment, geosynclines.
2. lake bed, compression
3. continental plates
4. crumple, lithosphere
5. anticlines, synclines

Answer 15

1. Sediment accumulates in depressions known as
   GEOSYNCLINES as rivers enter in those areas.
2. This creates a lake bed of layered sedimentary rocks as compression takes place.
3. Two continental plates converge due to convection currents.
4. This causes continental crust to crumple on top of the lithosphere due to pressure between the plates.
5. The continental crust starts to forms folds with anticlines and synclines which are pushed upwards to form fold mountains.

Question 16

Who theorised sea floor spreading and when?

Answer 16

Harry Hess in the 1940s.

Question 17

What does sea floor spreading provide evidence for?

Answer 17

Sea floor spreading provides evidence for tectonic plate movement.

Question 18

What is Palaeomagnetism?

Answer 18

Palaeomagnetism is the study of rocks that show the magnetic fields of the Earth.

Question 19

Evidence for seafloor spreading/tectonic plate movement (8)

1. formed and cooled, grains, and poles.
2. poles, periodically
3. opposite direction, older rock
4. Ocean floor, plate boundaries, symmetrical bands.

Answer 19

Harry Hess theorised sea floor spreading which provide proof for tectonic plate movement

Palaeomagnetism def.

As new rock is formed and cooled the magnetic grains within the rock align with the magnetic poles. Our poles (North and South) switch periodically. Each time these switch the new rocks being formed at plate boundaries align in the opposite direction to the older rock. On the ocean floor either side of constructive plate boundaries, geologists observed that there are symmetrical bands of rock with alternating bands of magnetic polarity. This is evidence of sea floor spreading.

Question 20

Explain how ocean trenches form (8)

Answer 20

1. Dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench.
2. This results in the seafloor bending to form a deep V-shaped depression.
3. Oceanic subduction zones almost always feature a small hill preceding the ocean trench itself. This hill, called the outer trench swell, marks the region where the subducting plate begins to buckle and fall beneath the more buoyant plate. This is known as the Benioff Zone.
4. The oceanic side is dominated by thick sedimentary rocks, while the continental side generally has a more igneous and metamorphic composition.

Question 21

What is the Peru-Chile trench.

Answer 21

The Peru-Chile Trench off the west coast of South America is formed by the oceanic crust of the Nazca plate subducting beneath the continental crust of the South American plate.

Question 22

What is the hadalpelagic zone, how does this relate to Oceanic trenches?

Answer 22

Ocean trenches occupy the deepest layer of the ocean, the hadalpelagic zone. (Deepest zone of the open ocean, starting at around 6,000 meters)

Question 23

Explain the formation of rift valleys (8)

Answer 23

1. Rift valleys occur at constructive margins in continental areas.
2. The heating and up-doming of the crust leads to fracturing and rifting.
3. As the sides of the rift move apart, central sections sections drop down to form rift valleys.

4.The largest rift valley is the Great East Africa Valley which extends 4000km and is 50km wide. The rift valley might widen further allowing the sea to inundate it, this may possibly cut of East Africa

Question 24

Explain how Mid-oceanic ridges form (8)

Answer 24

1. The plates diverge from each in opposite directions due to convection currents from heat in the asthenosphere.
2. As these plates move apart this leaves cracks and fissures that allows magma from the mantle to escape from the highly pressurised interior of the planet.
3. This magma rises through the gaps and erupts onto the surface and cools as new land.
4. The lava erupting is Basaltic. This means that the lava an travel long distances and creates gently sloping land features.
5. This can create huge ridges such as the Mid-Atlantic ridge with seamounts such as Tamu Massif in the northwest Pacific Ocean, sitting atop a triple junction of mid-ocean ridges. Also, Tristan da Cunha is an active strato-volcano in Saint Helens formed above a magma hot-spot some 400km east of the Mid-Atlantic Ridge.

Question 25

What is an example of a Mid-Ocean Ridge?

Answer 25

The Eurasian plate moves away from the North American plate at a rate of around 4cm per year. It is offset and has Transform faults running off it at right angles. These transform faults can cause earthquakes as they are prone to lateral movement.

Question 26

Explain how volcanic island arcs form (8)

Answer 26

1. Volcanic Island arcs are formed along a convergent plate boundary (e.g. The Pacific Ring of Fire has arcs along the Japanese, Mariana, and Aleutian Islands,) with a subduction zone between a continental and an oceanic plate.
2. Movement is generated by convection currents from heat in the asthenosphere. The denser oceanic plate is subducted below the continental plate.
3. The descending plate (oceanic plate), through the
   process of subduction is melted along the Benioff zone.
4. The molten magma
   then rises through the earth’s crust which cools and sets to create volcanoes, the basis for the arcs.
5. They occur as curved linear chains and may form two lines
   (extinct and active island arc systems).