Hazards - 1.1-1.3

Question 1

How are earthquakes distributed globally

Answer 1

• usually occur along plate boundaries (most powerful found at conservative boundaries)
• intraplate earth quakes occur near the middle of plates usually due to pre-existing weaknesses

Question 2

How are volcanoes distributed globally

Answer 2

• mainly found on convergent boundaries except from hotspot volcanoes
• hotspots such as Hawaii occur due to mantle plume
• around 70% of earthquakes found in the ring of fire

Question 3

What are the four layers of the earth and their composition

Answer 3

• inner core (solid)
• outer core (liquid)
• Mantle (solid but elastic)
• Crust (solid)

Question 4

What are the 3 layers of the mantle starting from shallowest and their composition

Answer 4

• Lithosphere (cool and brittle)
• Asthenosphere (ductile due to less pressure)
• Mesosphere (solid due to higher pressure)

Question 5

What are convection currents and how do they work

Answer 5

• the cores hot temperatures causes magma to rise in the mantle and sink towards the core when it cools
• the currents flow beneath the lithosphere building up lateral pressure carrying the plates with them

Question 6

What is slab pull theory

Answer 6

• at destructive margins the denser oceanic crust sinks into the mantle under the influence of gravity which pulls the rest of the plate along behind it

Question 7

What is sea floor spreading

Answer 7

• mid ocean ridges are formed when hot magma is forced up from the asthenosphere and hardens forming new oceanic crust
• the crust pushes the tectonic plates apart in this process of sea floor spreading

Question 8

What happens during subduction

Answer 8

• as new crust is being created in one places its being destroyed in another by subduction
• as two plate move towards each other, (oceanic and continental), the oceanic will slide under the continental into the mantle where it melts in the subduction zone

Question 9

What is paleomagnetism

Answer 9

• when the earths magnetic fields change direction causing the poles to swap
• when lava cools, minerals inside the rock lineup with earths magnetic direction

Question 10

What is an intraplate earthquake

Answer 10

found in the middle of tectonic plates caused by stress within a plate. Since plates move over a spherical surface zones of weaknesses are created

Question 11

What are hotspot volcanoes (mantle plumes)

Answer 11

Area in the mantle which heat rises as a hot thermal plume. High heat and low pressure at base of lithosphere enable melting of rock which rises through cracks in rocks causing volcanoes

Question 12

What is magnitude and intensity

Answer 12

Magnitude: measures the amount of energy released from the epicentre
Intensity: a measure of the ground shaking

Question 13

Describe the process of earthquakes

Answer 13

• movements are preceded by a gradual build up of tectonic strain which stores elastic energy in rocks
• when pressure exceeds the strength of the fault the rock fractures
• this produces the sudden release of energy, creating seismic waves
• the crust rebounds either side of the fracture (ground shaking) that is the earthquake felt on the surface

Question 14

What are the features of a body P-wave

Answer 14

• fastest and first to be received
• compressional wave
• travel through solid and liquid

Question 15

What are the features of a body S-wave

Answer 15

• slower - arrive after p wave
• up and down / side to side motion
• only travel through solid

Question 16

What are the features of surface waves (love and rayleigh)

Answer 16

• occur at lower frequency (slower)
• cause majority of damage
  Love
• faster, move horizontally
  Rayleigh
• rolling motion
• cause the most damage

Question 17

What are the primary hazards of earthquakes

Answer 17

• ground shaking: causes buildings, bridges, roads and infrastructure to collapse
• crust fracturing: when energy released causes the
  earths crust to crack

Question 18

What are the secondary hazards caused by earthquakes

Answer 18

• soil liquefaction: violent shaking causes surface rock to loose straight and become more liquid that solid -> subsoil looses ability to support building foundations
• landslides / avalanches: ground shaking places stress on slopes so they fail

Question 19

What are primary hazards of volcanoes

Answer 19

• lava flows: hot streams of lava up to 170 C. Slow moving so don’t threaten people
• Pyroclastic flows: mixture of hot rock, lava, ash, gas ejected at 100km/h (700C)
• Ash falls: disruptive as causes poor visibility and slippery roads causing roofs to collapse and engines to clogg
• Gas eruptions: magma contains dissolved gases (co2 / sulphur dioxide) that are released in the atmosphere and can be hazardous

Question 20

What are secondary hazards of volcanoes

Answer 20

• Lahars: masses of rock, mud and water travel down side of volcanoes fast (cant be outrun)
• Jokulhlaup: heat of eruption can melt snow/ice in a glacier causing sudden floods which are very dangerous