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Flashcards in Plate Tectonics Deck (80):
1

What are the layers of the Earth?

Core, mantle, crust.

2

What is the structure, composition and consistency of the core?

There is a solid inner core and a semi-molten outer core, both of which contain iron and nickel.

3

What is the structure, composition and consistency of the mantle?

The part of the mantle nearest the core is quite rigid, the layer above this (the asthenosphere) is semi-molten and the very top of the mantle is rigid too. The mantle is made mostly of silicate rocks.

4

What is the structure of the crust?

There is oceanic and continental crust. Continental crust is 30-70km thick and less dense. Oceanic crust is 6-10km thick and more dense.

5

What is the lithosphere?

The lithosphere is rigid mantle and crust, which is divided into tectonic plates.

6

What is the asthenosphere?

The asthenosphere is the semi-molten mantle.

7

What is the plate tectonics theory?

In the 17th century, people first noticed that South America and Africa looked like they could fit together, there were suggestions that the continents may once have been joined. In 1912, Alfred Wegener proposed the theory of continental drift, suggesting that all the continents were once joined as one supercontinent called Pangea 300 million years ago. The North was called Laurasia, and the South was called Gondwanaland.

8

What did Alfred Wegener base his theory on, and why wasn't it taken seriously initially?

Geological evidence and fossil records, but he couldn't back it up with a mechanism that explained how the continents moved.

9

Explain why there are convection currents in the asthenosphere and how they move tectonic plates.

Radioactive decay in the mantle and the core generates heat. When lower parts of the asthenosphere heat up, they become less dense and slowly rise. As they move towards the top of the asthenosphere they cool down, become more dense, and slowly sink. These circular movements of semi-molten rock are called convection currents. Convection currents create drag on the base of the tectonic plates and this causes them to move.

10

What is the cause of sea floor spreading/how do tectonic plates move?

Convection currents in the asthenosphere.

11

Explain the process of sea floor spreading.

Rising convection currents diverge at the base of the lithosphere, the drag of the convection currents causes the oceanic plates above them to diverge too. Magma rises up to fill the gap created, then cools to form new crust. Over time, the new crust is dragged apart and more new crust forms in-between.

12

What are the 5 pieces of evidence for the theory?

Geology, fossil records, living species, climatology and paleomagnetism.

13

How does geological evidence support the theory?

Areas of South America and Africa have rocks of the same age and composition, which line up when you fit the contents together. These rocks must have formed under the same conditions and in the same place in order to match so well.

14

How do fossil records support of the theory?

By fitting land masses together you can match up the distribution of some fossils (e.g. fossils of the mesosaurus). It is very unlikely that this species migrated over thousands of miles of water, or that they evolved in different places.

15

How do living species support the theory?

The same living organisms can be found on different continents (e.g. earthworms of the family megascolecidae are found in New Zealand, Asia and North America. It is very unlikely that this species migrated over thousands of miles of water, or that they evolved in different places.

16

Hoes does climatology support the theory?

There's evidence that the past climates of some continents were similar, despite being thousands of miles apart now. Large coal deposits that were formed in tropical conditions have been found in North America and parts of Europe, suggesting these regions were once closer to the equator than they are now.

17

How does palaeomagnetism support the theory?

Once every 200,000 years, the Earth's magnetic field reverses polarity. As magma erupts from mid-ocean ridges, magnetic materials in the molten rock align themselves with the direction of the Earth's magnetic field. When the crust has solidified, the alignment is fixed. The magnetic minerals in crust created in times of normal polarity are aligned in the opposite direction to those in crust created in periods of reverse polarity. This creates a series of alternating magnetic stripes along the sea floor. The stripes show that the crust is older the further away from a mid-ocean ridge you go, this means the plates are moving apart.

18

What is the evidence for sea floor spreading?

Palaeomagnetism.

19

What is the evidence for convection currents?

Continental drift.

20

Which hazards occur at constructive margins?

Earthquakes and volcanoes.

21

Which hazards occur at oceanic-continental destructive margins?

Earthquakes and volcanoes.

22

Which hazards occur at conservative margins?

Earthquakes.

23

In which direction do plates move at constructive margins?

Apart.

24

In which direction do plates move at destructive margins?

Towards each other.

25

In which direction do plates move at conservative margins?

Past each other.

26

What landforms are created at constructive margins?

Mid-ocean ridges and rift valleys.

27

How are mid-ocean ridges formed at constructive margins?

Where plates diverge beneath ocean, rising magma causes the oceanic crust to bulge and fracture, forming fault lines. As the plates keep moving apart, the crust between parallel faults drops down to form a rift valley. For example, the Mid-Atlantic Ridge.

28

How are rift valleys formed at constructive margins?

Where plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines. As the plates keep moving apart, the crust between parallel faults drops down to form a rift valley. For example, the East African Rift System.

29

How are volcanoes formed at constructive margins?

The mantle is under pressure from the plates above. When they move apart, the pressure is released at the margin. The release of pressure causes the mantle to melt, producing magma. The magma is less dene than the plate above, so it rises and can erupt to form a volcano.

30

How do earthquakes happen at constructive margins?

The plates don't move apart in a uniform way, some parts move faster than others. This causes pressure to build up. When the pressure becomes too much, the plate cracks , making a fault line and causing an earthquake.

31

What landforms are created at oceanic-continental destructive margins?

Deep sea trenches and fold mountains.

32

How are deep sea trenches formed at destructive margins?

The more dense oceanic crust is subducted under the less dense continental one (or less dense oceanic one), forming a deep sea trench. For example, the Peru-Chile trench.

33

How are fold mountains formed at destructive margins?

Fold mountains are made up of sediments that have accumulated on the continental crust, which are folded upwards along with the edge of the continental crust.

34

How are volcanoes formed at oceanic-continental destructive margins?

The oceanic crust is heated by friction and contact with the upper mantle, which melts into magma. The magma is less dense than the continental crust above and will rise back to the surface to form volcanoes.

35

How do earthquakes happen at oceanic-continental destructive margins?

As one plate moves under the other they can get stuck. This causes pressure to build up. When the pressure becomes too much the plates jerk past each other, causing an earthquake.

36

What landforms are created at oceanic-oceanic destructive margins?

Deep sea trenches and island arcs.

37

How are island arcs formed at destructive margins?

Volcanic eruptions that take place underwater create island arcs - clusters of islands that sit in a curved line. For example Mariana Islands.

38

How do earthquakes happen at oceanic-oceanic destructive margins?

The formation of a deep sea trench triggers earthquakes.

39

How are volcanoes formed at oceanic-oceanic destructive margins?

The formation of a deep sea trench triggers volcanic eruptions.

40

What landforms are created at continental-continental destructive margins?

Fold mountains.

41

How do earthquakes happen at continental-continental destructive margins?

Pressure builds up between the two plates moving together and can cause an earthquake.

42

What landforms are created at conservative margins?

Low ridges.

43

How do earthquakes happen at conservative margins?

The two plates get locked together in places and pressure builds up. As with destructive margins, this causes the plates to jerk past each other (or to crack, forming a fault line), releasing the energy as an earthquake.

44

What is a hot spot and how does it form volcanoes?

A hot spot is caused by a magma plume that rises up from the magma. Volcanoes form above magma plumes. The magma plume remains stationary, but the crust moves above it. Volcanic activity in the part of the crust that was above the hot spot decreases as it moves away . New volcanoes form in the part of the crust that is now above the hot spot. As the crust continues to move, a chain of volcanoes is formed. There's a hot spot in Hawaii.

45

What kind(s) of lava do you find at constructive plate margins?

Basaltic lava.

46

What kind(s) of lava do you find at destructive plate margins?

Andesitic and rhyolitic lava.

47

What is the silica content, viscosity and temperature of eruption of basaltic lava?

Low silica content, low viscosity (runny) and over 950 degrees celsius.

48

What is the silica content, viscosity and temperature of eruption of andesitic lava?

Medium silica content, medium viscosity and around 750-950 degrees celsius.

49

What is the silica content, viscosity and temperature of eruption of rhyolitic lava?

High silica content, high viscosity (thick) and less than 750 degrees celsius.

50

What are the characteristics of a basaltic lava eruption?

Non-violent, frequent and long-lasting eruptions.

51

What are the characteristics of an andesitic lava eruption?

Violent, intermittent and short-lived eruptions.

52

What are the characteristics of a rhyolitic lava eruption?

Violent, intermittent and short-lived eruptions.

53

What is intrusive volcanic activity?

Volcanic activity that takes place beneath the Earth's surface, such as formation of large magma chambers.

54

What is extrusive volcanic activity?

Volcanic activity that takes place on the Earth's surface. There are major (volcanic eruptions of lava) and minor forms (e.g. hot springs, geysers and boiling mud) of extrusive volcanic activity.

55

What are batholiths and how are they formed?

When large chambers of magma cool underground they form domes of igneous rock called batholiths. An example of a batholith is the Sierra Nevada batholith in the US.

56

What are dykes and sills and how are they formed?

Where magma has flowed into gaps in the surrounding rock and cooled, it forms vertical dykes and horizontal sills. Cooling cracks may form as the magma cools, in sills they're vertical and in dykes they're horizontal.

57

What are hot springs and why do they form?

Springs are places where groundwater emerges at the surface. When the groundwater source of a spring flows close to an area of recent intrusive volcanic activity, the water is heated and it becomes a hot spring.the temperature of hot springs varies from around 20-90 degrees celsius. They often have high mineral content because hot water can hold a lot of dissolved solids. An example of a group of hot springs are the ones in Rio Hondo in Argentina.

58

What are geysers and why do they form?

Geysers are a type of hot spring where hot water and steam are ejected from the surface in a fountain. They form in areas of intense volcanic activity. Groundwater is heated to above boiling point by magma deep in the crust. The hot water becomes pressurised and forces its way to the surface along cracks in the rocks. Finally, the hot water and steam spray out from a vent. Geysers erupt periodically, because they only erupt when the pressure is high enough to force the water out of the ground. An example of a geyser is Old Faithful in Yellowstone National Park in the US.

59

What are boiling mud pools and why do they form?

A boiling mud pool is a type of hot spring. They form in areas with very fine-grained soil, when the hot spring water mixes with the soil. The pools sometimes contain brightly-coloured mud because of minerals deposited by the hot water. There are boiling mud pools in Yellowstone National Park in the US.

60

What do dome volcanoes look like, what margins do they occur at, and what kind of lava do they have? Give an example.

Steep sides caused by high viscosity of lava, with a central vent and made up of layers of lava. They often occur at destructive margins, with rhyolitic or andesitic lava. An example of a dome volcano is Puy De Dome in France.

61

What do caldera volcanoes look like, what margins do they occur at, and what kind of lava do they have? Give an example.

Very wide circular crater, which can be several kilometres across. The central part of the volcano has collapsed as the magma chamber below has emptied. Made up of layers of lava, ash and cinders. They often occur at destructive margins, with rhyolitic or andesitic lavas. An example of a caldera volcano is Aira Caldera in Japan.

62

What do shield volcanoes look like, what margins do they occur at, and what kind of lava do they have? Give an example.

Gently sloping sides caused by low viscosity lava, with a central vent and made up of layers of lava. They often occur at constructive margins or hotspots, with basaltic lava. An example of a shield volcano is Mauna Loa in Hawaii.

63

What do fissure volcanoes look like, what margins do they occur at, and what kind of lava do they have? Give an example.

Fairly flat surface caused by low viscosity of lava, with a long linear vent and made up of layers of lava. They often occur at constructive margins, with basaltic lava. An example of a fissure volcano is the Laki Fissure System in Iceland.

64

What is the main cause of earthquakes?

Earthquakes are caused by tension that builds up at all three types of plate margin. When the plates jerk past each other it sends out seismic waves (vibrations). These vibrations are the earthquake and they spread out from the focus.

65

Apart from movement at plate boundaries, how else may an earthquake be caused?

Reactivation of old fault lines that have not been active for a long time, subsidence (when the ground sinks) as a result of deep mining, and pressure on surface rocks from water in large reservoirs.

66

What is the focus?

The place in the lithosphere where the earthquake starts.

67

What is the epicentre?

The point on the Earth's surface directly above the focus.

68

What are the three types of seismic waves?

P (or primary) waves, S (or secondary) waves and surface waves.

69

What are the characteristics of P waves?

P waves can travel through solids and liquids, they push and pull the earth in the same direction as the wave is travelling and they are the fastest seismic wave.

70

What are the characteristics of S waves?

S waves can only travel through solids, they move the earth at 90 degrees to the direction of travel and they can cause a lot of damage because of their shearing effect.

71

What are the two types of surface waves?

Love waves and rayleigh waves.

72

What are the characteristics of love waves?

Love waves can only travel through solids, they move the surface from side to side, they cause a lot of damage because of their shearing effect and they travel more slowly than P and S waves.

73

What are the characteristics of rayleigh waves?

Rayleigh waves can travel though liquids and solids, they move the surface in a rolling motion and they travel more slowly than P and S waves.

74

How can you measure earthquakes?

The amount of energy released by an earthquake can be measured using a seismometer. Seismometers measure the magnitude of the earthquakes as well as the duration and direction of the vibrations. Seismic records have been built up over time, which allow us to look at the frequency of earthquakes in different areas.

75

What are the two different scales used to measure earthquakes?

The Richter and Mercalli scale.

76

What are the characteristics of the Richter scale?

The Richter scale measures the magnitude of an earthquake. It doesn't have an upper limit and it's logarithmic (an earthquake measuring 5 has an amplitude ten times greater than one with a magnitude of four.

77

What are the characteristics of the Mercalli scale?

The Mercalli scale measures the impacts of an earthquake, measured using observations of the event. The scale is between 1 and 12, with 1 being an earthquake only detected by instruments, and 12 being an earthquake that causes total destruction.

78

How do earthquakes cause tsunamis?

The earthquakes cause the seabed to move, which displaces water. Waves radiate out from the epicentre of the earthquake. The greater the movement of the sea floor, the greater the volume of water displaced and the bigger the wave produced.

79

Apart from an earthquake, how else could a tsunami be caused?

Volcanic eruptions and landslides that slide into the sea can also displace large amounts of water and cause a tsunami.

80

What is a tsunami and what are the characteristics of one?

Tsunamis are large waves caused by the displacement of large volumes of water. In the open ocean where the water's very deep, the waves travel at high speeds of about 500-950km/h, with a long wavelength of about 200km, and a small amplitude of about 1m. Closer to land the water gets shallower. This causes the waves to get compressed and their energy becomes more concentrated. The waves slow down to less than 80km/h, their wavelength decreases to less than 20km, and their amplitude increases to many metres. Just before the tsunami reaches the coast, the water withdraws down the shore. The wave then hits with great force, but only travels a short distance inland.