Tectonics EQ1

Question 1

What is the asthenosphere?

Answer 1

Close to the surface, the low pressure create the ductile upper zone of the mantle

Question 2

What is the lithosphere?

Answer 2

The crust and upper mantle together, rock becomes cool and more brittle close to the surface of the mantle.

Question 3

What are the different types of crust?

Answer 3

Oceanic –> thin

Continental –> thick and lower in density than oceanic crust so it is able to float

Question 4

What % of earthquakes are found in the “Ring of Fire” in the Pacific Ocean?

Answer 4

75%

Question 5

Describe the two parts of the core?

Answer 5

Inner Core: Hottest - 6000C, solid, mostly Iron

Outer Core: semi-molten, mostly liquid iron and nickel, temps 4,500-6000C

Question 6

Describe the distribution of earthquakes?

Answer 6

The main earthquake zones are found, often in clusters, along plate boundaries; typically powerful earthquakes are associated with convergent or conservative boundaries. Apart from at plate boundaries, intra-plate earthquakes do occur along old fault lines, such as the Church Stretton Fault in Shropshire.
The oceanic fracture zone (OFZ) is a belt of activity through the oceans along the mid-ocean ridges, coming onshore in Africa, the Red Sea, the Dead Sea rift and California. Mid-ocean ridges such as the Mid-Atlantic Ridge are places in the Earth’s tectonic plate system where new crust forms and the plates move away from one another The CFZ is a belt of activity following the mountain ranges from Spain to the Pacific via the Alps, the Himalayas etc.

Question 7

Describe the distribution of volcanoes

Answer 7

• Near subduction zones such as the Pacific ring of fire, this often has the most violent of all activity
• Along divergent ridges e.g Mid-Atlantic ridge
• Along rift valleys (same as above just on land) e.g Mt Kilimanjaro
• A volcanic hotspot = area in mantle where heat rises as hot thermal plume from deep in earth, the magma rises through cracks and erupts to form active volcanoes on the Earth’s surface –> as tectonic plates move over the stationary hotspot, volcanoes also move and are replaced by new ones in their place. As oceanic volcanoes move away from the hotspot, they cool and subside, producing older islands –> can create chains of islands over time e.g Hawaiian Islands

Question 8

What is a convergent/ destructive plate boundary in simplest terms?

Answer 8

Where two plates colide

Question 9

What are divergent/constructive plate boundaries in simple terms?

Answer 9

Where two plates move apart

Question 10

What are conservative/transform plate boundaries in simplest terms?

Answer 10

Where two plates slide past each other

`

Question 11

How many active volcanoes are there in the world and how often do they erupt each year?

Answer 11

There are about 500 volcanoes globally, around 50 erupt each year.

Question 12

Describe the distribution of Tsunamis

Answer 12

90% of all events occur within the Pacific Basin, in association with the activity at plate margins. Most are generated at subduction zones (convergent boundaries), particularly off the Japan-Taiwan island arc, South America and the Aleutian Islands

Question 13

What are the causes of tsunamis?

Answer 13

When a sub-marine earthquake displaces the sea bed vertically as a result of movement along a fault line at a subduction zone. This violent movement displaces a large volume of water in the ocean water column, which then moves outwards in all directions from the point of displacement.
Sub-marine earthquakes that occur close to the shoreline can generate intense ground shaking damage, followed by subsequent tsunami

Question 14

Who coined the term continental drift and what does it mean?

Answer 14

Alfred Wegener in 1912. He believed that there was a single supercontinent called Pangea that existed about 300 million years ago. This was only evidenced in the early 1960s when seafloor spreading was validated by the scientific community

Question 15

Name the 5 pieces of evidence that support Wegeners’ theory of continental drift (i.e that there was once one supercontinent)

Answer 15

REMEMBER THESE ARE NOT THEORIES, BUT EVIDENCE THAT CONTINENTAL DRIFT HAPPENED

1. Jigsaw Fit
2. Geological Fit
3. Tectonic Fit
4. Glacial deposits
5. Fossil Evidence

Question 16

Describe the Jigsaw Fit evidence for plate tectonics

Answer 16

The similarity in outline of the coastlines of eastern South America and West Africa had been noted for some time. The best fit is obtained if the coastlines are matched at a depth of 1,000 metres below current sea level
Why there are gaps or overlaps and not a constant jigsaw fit:
- Coastal erosion since separation of continents
- Coastal deposition since
-Rises in sea level (eustatic change) since seperation
-changes in land level (isostatic change) since separation

Question 17

Explain the geological fit as evidence for plate tectonics

Answer 17

Ancient rock outcrops over 2,000 million years old were the same in both eastern South America and West Africa
Also, rock sequences in northern Scotland are similar with those of

Question 18

Explain the geological fit as evidence for plate tectonics movement

Answer 18

Ancient rock outcrops over 2,000 million years old were the same in both eastern South America and West Africa
Also, rock sequences in northern Scotland are similar with those of Eastern Canada, indicating they were laid down under the same conditions in one location

Question 19

Explain tectonic fit as evidence for continental drift

Answer 19

Fragments of old fold mountain belt between 450 and 400 million years ago are found on widely separated continents today. Pieces of the Caledonian fold mountain belt are found in Greenland, Canada, Ireland, England, Scotland and Scandinavia. When these land masses are re-assembled the mountain belt forms a continuous linear feature

Question 20

Explain glacial deposits as evidence for continental drift

Answer 20

Today, glacial deposits formed during the Permo-Carboniferous glaciation (about 300 million years ago) are found in Antarctica, Africa, South America, India and Australia.
If the continents havent mood then this would suggest an ice sheet extended form the south pole to the equator at this time - very unlikely.
But if the continents of the southern hemisphere re-assembled near the south pole then the Permo-Carboniferous ice sheet assumes a much more reasonable size. More evidence comes from glacial striations - scratches on the bedrock made my blocks of rock embedded in the ice as the glacier moves. These show the direction of the glacier, and suggest the ice flowed from a single central point

Question 21

Explain fossil evidence for continental drift

Answer 21

There are many examples of fossils found on seperate continents and nowhere else, suggesting the continents were once joined.
i.e same fossil Mesosaurus can be found on South American East coast and African West Coast

Question 22

How does the theory of Mantle Convection explain how the plates move

Answer 22

Heat produced by the decay of radioactive elements in the earths core heats the lower mantle, creating convection currents. Heat radiates outwards from the inner core. These hot, liquid magma currents are thought to move in circles in the asthenosphere, causing the plates to move.
Less accepted now as the reason for plate movement as rate of convection is less than observed rates of plate movement.

Question 23

How does the theory of slab pull and ridge push explain tectonic plate movement?

Answer 23

Convection currents in the mantle move tectonic plates as the asthenosphere circulates due to heat present in the core. Where subduction is occuring, this results in a force known as slab pull. This is created as the plates begin to sink into the earths mantle and serves to pull the lower plate further away from the volcanic ridge where it is formed. Where new oceanic crust is formed at mid-ocean ridges, it pushes the tectonic plates apart.
The newly formed oceanic crust is denser than the asthenosphere that it sits upon so it begins to sink (at subduction zones), pulling apart the mid-ocean ridge allowing for more magma to rise.

Question 24

How do Subduction Processes and the Benioff Zone theory help to explain tectonic plate movement?

Answer 24

The subduction zone is the broad area where two plates are ,oving together, often with the more dense oceanic plate sinking beneath the continental plate. As a new plate is being created in one place, it is being destroyed in another. Benioff zones are dipping zones of increased earthquake activity produced by the interaction of the sinking oceanic crustal plate with an overriding continental or oceanic plate. They occur at subduction zones
The area of seismicity corresponding with the slab being thrust downwards is the Benioff zone. The different speeds and movements of the rocks at this point produce numerous earthquakes. This theory is important in determining the earthquake magnitude as it determines the position and depth of the hypocentre (the focus point where the strain energy of the earthquake stored in the rock is released)

Question 25

How does Sea Floor Spreading help explain tectonic plate movement?

Answer 25

Mid-ocean ridges are formed when magma (molten rock) is forced up from the asthenosphere and hardens, forming new oceanic crust. This new crust pushes the tectonic plates apart in a process called seafloor spreading.
Palaeomagnetism is the study of the history of Earth’s magnetic field. The direction of Earth’s magnetic field changes direction once every 200,000 - 400,000 years (polarity reverses) - meaning the north and south poles switch. As magma erupts from mid-ocean ridges the magnetic minerals in the molten rock align themselves with the direction of the Earth’s magnetic field. So, magnetic minerals (e.g iron) in the crust created during periods of normal polarity (north pole is magnetic north) are aligned in the opposite direction of those created in periods of reverse polarity (magnetic north is in south pole). This creates alternating magnetic strips along the sea floor. It is possible to follows these bands of crust created under different polarity and determine that the further away from the mid-ocean ridge the older the crust is, showing the plates are moving apart

Question 26

Explain a primary hazard of a volcano (Pyroclastic Flows)

Answer 26

• Mixture of dense hot rock, lava, ash and gases ejected from a volcano, which move very quickly along the earths surface
• They destroy everything they touch and travel at very high speeds making them particularly dangerous
• They are extremely hot ( up to 700 degrees Celsius) and travel at 100km per her

Question 27

Explain a primary hazard of a volcano (Lava Flows)

Answer 27

• Streams of lava that have erupted onto earths surface
• Very hot (up to 1700 degrees Celsius)
• Can take years to cool completely
• Not so much a threat to humans because people can escape them as they move much slower

Question 28

Explain a primary hazard of volcanoes (Volcanic gases)

Answer 28

• Gases dissolved in Magma are released into the atmosphere during volcanic eruptions
• Water vapour (80%)
• CO2
• Sulphur Dioxide
• Can travel thousands of kilometres

Question 29

Explain a primary hazard of volcanoes (Tetra and Ash falls)

Answer 29

• Tephra = pieces of volcanic rock and ash that are blasted into air during volcanic eruption
• The larger pieces tend to fall nearer the volcano, causing death and injury
• The smaller pieces can travel thousands of kilometres
• Ash falls can be very disruptive. Where ash lands it covers everything - making roads slippery and poor visibility. Roofs may collapse under the weight and engines can get clogged up

Question 30

Explain a secondary hazard of volcanoes (Lahars)

Answer 30

• Masses of rock, mud and water that travel quickly down the side of a volcano
• Volcanic mudflows composed of fine silt and sand
• Vary in size and speed
• The largest can be hundreds of miles wide and flow tens of metres per second
• They are caused when an eruption quickly melts snow and ice
• OR they can occur where heavy rainfall erodes loose rock and soil causing it to surge downslope
• The degree of hazard depends on how steep the slopes are, the volume of material and particle size

Question 31

Explain a secondary hazard of volcanoes (Jokulhlaup)

Answer 31

• The heat of a volcanic eruption can melt the snow and ice in a glacier - causing heavy and sudden floods known as Jokulhlaup)
• These floods can be very dangerous because they suddenly release large amounts of water, rock, gravel and ice that can catch people off guard and damage land and structures
• They can occur anywhere where water accumulates in a subglacial lake beneath a glacier
• The flood is iniated following the failure of a dam

Question 32

Tsunami (keyword) & Characteristics

Answer 32

Initiated by underwater earthquakes, landslides and sometimes volcanic eruptions. A tsunami is a sequence of waves with deep troughs between them.
Characteristics:
Long wavelengths : 150-100km
Low amplitude (wave height): 0.5 - 5m
Fast velocities, up to 600kph in deep waters

Question 33

Describe a case study of a Tsunami

Answer 33

Stages of the 2011 Tohoku Tsunami: a 9.0 magnitude earthquake under the Pacific ocean, the waves reached 10 metres high and surged up to 10km inland

• The plates are pushing together which eventually slip and release all the stored strain energy
• The energy is transferred into the water, the water above suddenly moves up when the seabed is lifted upwards, creating a wave (displacing the water column)
• The wave moves out from where the earthquake hit travelling at high speeds
• As the waves reach shallow waters the front of the wave slows and the back catches up, this causes the wave to get taller and eventually crashes into the land