Hazardous Earth

Question 1

What is the structure of the earth?

Answer 1

The earth is made up of an inner core, outer core, mantle and crust

Question 2

What is the crust like?

Answer 2

-0-100km long
-Consists of the oceanic(more dense) and continental(less dense) plate
-oceanic thickness is 5-10km
-continental thickness is 30-70km

Question 3

What is the mantle like?

Answer 3

-100-2900km long
-The upper mantle contains the lithosphere and belown it the asthenosphere(100-300km)
-Lithosphere (semi-core) The top part of the mantle
Rigid and stuck to the underside of the crust Varies in thickness Boundary with asthenosphere difficult to define (melts and becomes incorporated in asthenosphere)
-Asthenosphere extends 100-300km Semi-molten/viscous - Allows rock to move due to high pressure in mantle. Flowing slowly
-It also has a lower mantle

Question 4

What is the core like?

Answer 4

-Consists of a liquid outer core and solid inner core
-Liquid outer core is 2883km to 5140km thick
-Solid inner core is 5140km to 6371km thick

Question 5

Where do convection currents exist and What do these do?

Answer 5

They occur in the Asthenosphere and are caused by vast amounts of heat generated in mantle.They pull on the underside of the lithosphere causing it to move, resulting in plate movement

Question 6

Explain the movement of the crust caused by convection currents in the mantle:

Answer 6

-Hot rock rises from lower to upper asthenosphere.
-Hot rock spreads and cools, pushing plates apart.
-Cool rock sinks back down towards core.
-As (oceanic) plate subducts at ocean trenches, gravity pulls it under
-Rising mantle pushes crust upwards at mid-ocean trenches, while gravity pulls it back down

Question 7

Who is Alfred Wegner?

Answer 7

Alfred Wegener (1880-1930), a German meteorologist and geologist, was the first person to propose the theory of continental drift

Question 8

What was Wegners idea of continental drift?

Answer 8

He proposed that in the carboniferous period, 250 million years ago, a large single continent pangea existed. This slowly broke apart into 2 large land masses. This movement slowly continued to the present day as the continents separated and spread across the globe.

Question 9

What is the geological evidence for continental drift?

Answer 9

-The fit of continents such as South America and Africa on either side of the Atlantic
-Evidence from about 290million years ago of the effects of contemporaneous glaciation in southern Africa , Australia, South America, India and Antarctica, suggesting that these land masses were joined at this time, located close to the south pole
-Mountain chains and some rock sequences on either side of Oceans show great similarity, e.g. northeast Canada and northern Scotland

Question 10

What is the biological evidence for continental drift?

Answer 10

-Similar fossil brachiopods (marine shellfish) found in Australian and Indian limestones
-Similar fossil animals found in South America and Australia, especially marsupials
-Fossils from rocks younger than the Carboniferous period, in places such as Australia and India, showing fewer similarities , suggesting that they followed different evolutionary paths

Question 11

What are other pieces of evidence for continental drift?

Answer 11

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Question 12

Who is Marie Tharp?

Answer 12

Marie Tharp is a celebrated cartographer who contributed to a revolution in geological thinking - mapping the seafloor revealing the existence of mid-ocean ridges around the globe.

Question 13

What 4 things can be used as evidence of the sea floor spreading?

Answer 13

-Paleo magnetism
-Ruggedness (mountains)
-Age
-Volcano and earthquake distribution

Question 14

How can paleomagnetism be used as evidence of the sea floor spreading?

Answer 14

-During the history of the Earth the direction of magnetic north has frequently changed/reversed.
Thus, sometimes rocks are magnetised to the North and sometimes to the South
-Igneous rocks, form part of the oceanic crust and ocean floor. These rocks contain iron particles and as lava erupts, it cools and the magnetic orientation of the iron is locked into the rock, depending on the Earth’s polarity at the time. Earth’s polarity is not constant, it changes every 400,000-500,000 years and this is recorded in the rocks on the ocean floor
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Question 15

How can ruggedness be used as evidence for the sea floor spreading?

Question 16

How can age be used as evidence for the sea floor spreading?

Answer 16

-During the 1960s, an ocean-drilling programme was established to investigate ocean sediments and crustal
rocks in the deep ocean.
-Drilling recovered cores in water up to 7,000m deep and revealed a spatial pattern of sediments. This supported sea-floor spreading theory.
-Thick and old sediments were found near continents.
-Nowhere in the oceans was rock older than 200 million years – confirming that ocean crust was constantly recycled over this period

Question 17

How can the volcano and earthquake distribution be used as evidence for the sea floor spreading?

Question 18

What is sea floor spreading?

Answer 18

Lateral movement of new oceanic crust away from a mid-ocean ridge (constructive plate boundary)

Question 19

How does sea floor spreading provide evidence for continental drift?

Answer 19

-Sea-floor spreading moves material across ocean floors.
-Newest rock is found in the middle (at mid-ocean ridge), therefore new rock is being created here - these palaeomagnetic stripes show that each one is mirrored either side of the mid-ocean ridge, showing that new crust is being created here before it moves apart
-Rocks are not the same age as the earth (4.5 billion years) meaning oldest rock is being destroyed and replaced by newer rocks - also shows new crust is being created
-Indicates that, as fresh molten rock from asthenosphere reaches ocean bed, ‘older’ rock is pushed away from the mid-ocean ridge.
-Oldest rock would be located furthest from the point it is created (nearer land).
-Eventually, the sea floor reaches an ocean trench where material is subjected into the asthenosphere and becomes semi-molten (caused by convection currents).

Question 20

How does the global patterns of plate boundaries provide evidence for continental drift?

Answer 20

-Earthquakes are concentrated in narrow bands at plate boundaries (rigid lithosphere and crust broken up into tectonic plates that are moving) - there is an obvious pattern that most volcanic eruptions and earthquakes occur around the edges of plates, e.g. the Pacific Ring of Fire, where the most movement occurs (evidence for continental drift)
-Although there are some in the centre of plates, there is an obvious pattern

Question 21

How do subduction zones provide evidence for continental drift?

Answer 21

-Where plates collide, fold mountains and ocean trenches prove that the plates are moving towards each other
-The Benioff zone in ocean trenches, where oceanic crust is being subducted, experiences earthquakes occurring below sea level - this proves that plates are subducted
-Volcanic activity also occurs on these boundaries due to the melting of the subducted plates - volcanic activity proves plate movement

Question 22

How do hot spots provide evidence for continental drift?

Answer 22

-Hot spots are mantle plumes - a convection current must be set up as lava rises. If there is a heat differential, a convection current will be set up
-Hot spots are able to record the movement of plates over a mantle plume, e.g the Hawaii hotspot movement
-There is little evidence for this, as convection currents can’t be modelled in the mantle, only on a smaller scale in labs.
-For this theory to be correct, we are assuming convection currents in the mantle will act the same way as on a small scale - this makes the evidence unconvincing due to the lack of support

Question 23

How do plates floating on the mantle provide evidence for continental drift?

Answer 23

-Seismic profiling allows you to identify layers beneath the surface. The wave will be reflected if there is a sudden change in rock type, indicating that there are different layers. However, this provides little evidence as to how many layers are beneath the surface, and doesn’t prove the mantle is a liquid layer.
-Ophiolite sequences are a full section of the ocean crust, found in crumple zones in fold mountains. However, these sequences contain variably altered oceanic rocks, with only a small part of the mantle to examine, so these are often unconvincing.
-Shield volcanoes reveal what is under the crust

Question 24

What is the global pattern for plate boundaries?

Answer 24

Earthquakes are concentrated in narrow bands at plate boundaries (rigid lithosphere and crust broken up into tectonic plates that are moving)

Question 25

What are the 3 types of plate boundaries?

Answer 25

-Divergent (constructive)
-Convergent (destructive)
-Transform (conservative)

Question 26

What are the features and processes of a divergent plate boundary?

Answer 26

-Plates move apart, magma from the mantle fills the gap forming new oceanic crust
-E.g mid Atlantic ridge
-Landforms: Rift valleys, mid ocean ridges and shield volcanoes
-Hazards: Volcanic activity, minor earthquakes

Question 27

What are the features and processes of a convergent plate boundary?

Answer 27

• (Oceanic-continental) Denser oceanic plate sub-ducts under continental plate, forming trenches and volcanic mountain ranges e.g. Andes mountains
  -(Oceanic-oceanic) One oceanic plate subducts under the other, creating deep ocean trenches and volcanic island arcs e.g. Mariana Trench
  -(Continental-continental) Collision with no subduction due to similar densities, forming high mountain ranges e.g. Himalayas
  -Hazards: Earthquakes, volcanic eruptions, tsunamis

Question 28

What are the features and processes of a conservative plate boundary?

Answer 28

-At transform boundaries, plates slide past each other horizontally
-Crust is neither created nor destroyed, but the friction between plates often leads to earthquakes. E.g San Andreas fault in California where the pacific and North American plates slide past each other, producing frequent earthquakes and the Alpine Fault in New Zealand where the pacific and ind-Australian plates slide past each other.

Question 29

What are explosive eruptions?

Answer 29

-Found at convergent plate boundaries, where magma is viscous and rich in silicia, leading to violent explosions
-Volcano types include strato-volcanoes (composite Cone volcanoes) with layers of ash and lava, which can build up intense pressure
-Calderas are volcanic craters usually more than 2km in diameter and from when an explosive eruption causes the volcano to collapse, leaving a large crater
-E.g. The 1883 eruption in Krakatoa in Indonesia left a caldera 7km wide

Question 30

What are effusive eruptions?

Answer 30

-Occur at divergent plate boundaries where magma as low viscosity and low silicia content, allowing lava to flow more easily
-Shield volcanoes with gentle slopes form through effusive eruptions as seen in Iceland
-Lava Plateux form when large volumes of low viscosity lava flow over extensive areas, such as the Deccan plateau in India which covers more than 500,000km squared known as the large igneous province while the Colombia plateau in the northwest USA covers 130,000km squared

Question 31

What are the volcanic hazards associated with effusive/explosive eruptions?

Answer 31

-Lava flow
-Pyroclastic flows
-Ash flows
-Lahars
-Volcanic gases
-Volcanic bombs and tephra

Question 32

What are lava flows?

Answer 32

-Lava flows are streams of molten rock that emerge from a volcanic vent
-They can be slow moving, giving people time to evacuate, but they cause extensive destruction=tin by incinerating buildings, roads and vegetation
-Basaltic lava is fluid and spreads far while andestic and rhyolitic lavas are more viscous and flow less readily

Question 33

What are pyroclastic flows?

Answer 33

-These are fast moving , ground hugging clouds of hot gas, ash and volcanic debris that can reach over speeds of 100km/hr and temperature around 400-700 degrees Celsius
-They can destroy everything in their path and can travel several km from the eruption site
-Highly lethal de to their speed, temperature and density

Question 34

What is ash fall?

Answer 34

-Volcanic ash consists of fine particles of volcanic rock and glass
-When ejected into the atmosphere, it can settle over wide areas, disrupting transportation, damaging machinery, contaminating water supplies and affecting health
-Ash fall can also lead to building collapse if it accumulates heavily on rooftops and disrupt agriculture by burying crops

Question 35

What are Lahars?

Answer 35

-Lahars are volcanic mudflows that occur when volcanic debris mixes with water form rainfall, melted snow or ice
-These flows move rapidly down river valleys, carrying boulders, ash and mud
-Lahars can be highly destructive, burying entire communities and they can persist for years after an eruption due to repeated rainfalls

Question 36

What are volcanic gases?

Answer 36

-Volcanoes release gases such as sulfur dioxide, carbon dioxide, hydrogen sulfide and water vapour
-Sulfur dioxide can lead to acid rain and respiratory issues, while CO2 in high concentrations can cause suffocation, especially in low-lying areas
-These gases can also impact the climate, as sulfur dioxide can reflect sunlight, causing temporary cooling

Question 37

What are volcanic bombs and tephra?

Answer 37

-Volcanic bombs are large fragments of lava that cool into solid rock before hitting the ground, while tephra includes all airborne volcanic material
-These materials can cause injuries or fatalities on impact and damage structures within the blast zone