why are some locations more at risk from tectonic hazards?

Question 1

the global distribution of plate boundaries can be explained by what?

Answer 1

plate boundaries and other tectonic processes

Question 2

describe the earth’s structure

Answer 2

the inner core, outer core, mantle, crust

Question 3

what are the two main tectonic plates? and what’s the difference between them.

Answer 3

oceanic:
-underwater 
-thinner than continental crust
-dense so it sinks
-newer rocks
  continental 
-on land 
-thicker than oceanic crust
-less dense (so it floats)
older rocks

Question 4

what are seismic waves?

Answer 4

shock waves released by tectonic movements

Question 5

what are the four theories explaining plate tectonic movement?

Answer 5

Mantle Convection
Slab pull
Subduction
Seafloor spreading.

Question 6

describe was is meant by mantle convection

Answer 6

Heat produced by the radioactive decay of material in the earth’s core heats the lower mantle-creating convection currents. These hot liquid magma currents are thought to move in circles through the asthenosphere causing the plates to move.

Question 7

describe what is meant by Slab Pull

Answer 7

Newly formed oceanic crust at mid-ocean-ridges become denser and thicker when it cools. this causes it to sink into the mantle under its own weight- pulling the rest of the plate further down with it.

Question 8

describe what is meant by subduction

Answer 8

As two oceanic plates (or one oceanic and one continental) move towards each other, one (usually the denser one) slides under the other into the mantle- where it melts in an area known as a subduction zone

Question 9

describe what is meant by seafloor spreading

Answer 9

in the middle of many oceans are huge mid-ocean ridges (underwater mountain ranges). These are formed when hot magma is forced up from the asthenosphere and hardens (cooled). This forms a new oceanic crust which pushes the tectonic plates apart in a process called seafloor spreading.

Question 10

what are the three different plate margins?

Answer 10

Destructive
Constructive
Conservative plate boundary

Question 11

what happens at the conservative plate margin and what do they form?

Answer 11

Plates slide past each other

earthquakes

Question 12

what happens at destructive plate margins and what do they form?

Answer 12

Plate slides under another plate
forms volcanos and earthquakes

(destructive collision zones)
Plates move towards each other
both plates are forced up and form fold mountains

Question 13

what happens at constructive plate margins and what is formed?

Answer 13

plates move away from each other

forms volcanoes

Question 14

what are some theories of plate motion?

Answer 14

• Alfred Wegener’s continental drift hypothesis in 1912 suggested that now-separated continents had once been joined as a continent names Pangea
• Arthur homes suggested in 1930 that the earth’s internal radioactive heat was the driving force of mantle convection that could enable the movement of tectonic plates
• the discovery in 1960 of the asthenosphere, a weak, deformable layer beneath the rigid lithosphere on which the lithosphere moves
• paleomagnetism involving ancient magnetism which causes the plates to move

Question 15

what are transform zones?

Answer 15

where conservative plate boundaries consist of transform faults. These faults join up as they traverse the earth’s surface in a zig-zag pattern. Long transform faults like the San Andreas fault creates an area of frequent earthquake activity.

Question 16

what are the causes of earthquakes?

Answer 16

Earthquakes are a result of a sudden release of stored energy. As tectonic plates attempt to move past each other along fault lines, they inevitably ‘stick’. This allows pressure to build up over time which is suddenly released (stick-slip behaviour). energy radiates out in all directions from the earthquake’s focus. in some cases, the earthquakes motion displaces the surface, creating a fault scarp.

Question 17

what are the three types of waves earthquakes create?

Answer 17

P-waves: primary waves (fastest and cause the least damage)
S-waves: secondary waves (second fastest and shake ground violently causing damage)
L-waves: love waves (slowest, have a large amplitude and cause significant damage, Inc. fracturing the ground’s surface).

Question 18

what are some secondary impacts of earthquakes?

Answer 18

landslides- most prone in areas of geologically young (and therefore unstable) earthquakes such as the Himalayas
liquefaction- areas where the ground consists of loose sediment such as silt, sand or gravel that is also waterlogged (often found near sea of rivers).

Question 19

what are six secondary hazards of volcanos?

Answer 19

• LAVA FLOW: extensive areas of solidified lava which can extend several kilometres from the volcanic vents
• PYROCLASTIC FLOW: very large, dense clouds of hot ash and gas of temperatures of up to 600°C.
• ASHFALL: ash particles and larger tephra particles can blanket huge areas in ash, killing vegetation, collapsing buildings and poisoning water sources
• GAS ERUPTION: the eruption of carbon dioxide and sulphur dioxide, which can poison people and animals in extreme cases
• LAHAR: volcanic mudflows, which occur when rainfall mobilises volcanic ash. They can travel at high speed down river systems and cause major destruction.
• JÖKULHLAUP: devastating floods caused when volcanoes erupt beneath glaciers, and ice caps, creating huge volumes of meltwater. They are common in Iceland.

Question 20

which of the volcanic secondary hazards occur in a composite volcano/subduction zone?

Answer 20

• lava flow
• pyroclastic flow
• ashfall
• gas eruption
• lahars

Question 21

which of the volcanic secondary hazards occur in a shield volcano?

Answer 21

• lava flow

- gas eruption

Question 22

which of the volcanic secondary hazards occurs on a constructive plate margin?

Answer 22

• ashfall

- Jökulhlaup

Question 23

what are ways in which a tsunami is formed?

Answer 23

• landslides
• eruptions of volcanic islands
• (most commonly) sub-marine earthquakes in subduction zones.

Question 24

describe how a tsunami is formed as a consequence of a sub-marine earthquake

Answer 24

Tsunamis are generated when a sub-marine earthquake displaces the sea bed vertically (either up or down) as a result of movement along the subduction zone or along a fault line.
The violent motion displaces a large volume of water in the ocean water column, which then moves outwards in all directions from the point of displacement.
the water moves as a vast ‘bulge’ in open water, rather than as a distinct wave.

Question 25

what are some characteristics of a tsunami?

Answer 25

• wave height of typically less than 1m
• wavelengths are usually more than 100km.
• speeds are 500-950km/h.

Question 26

what’s the difference between tsunamis in the open ocean and close to shore?

Answer 26

• out at sea: barely noticeable

- close to shore: wavelength drops but wave height increases making them noticeable.