1.3 physical processes explain causes of tectonic hazards

Question 1

earthquake hazards - what are P waves

Answer 1

• primary waves
• body wave
• fastest so they arrive first
• travel through solids and liquids
• caused by pushing and pulling in direction of travel
• cause shaking forward and backwards
• least damaging

Question 2

earthquake hazards - what are S waves

Answer 2

• secondary waves
• body wave
• slower than P waves
• only travel up and down in solids
• cause sideways motion
• more damaging than P waves

Question 3

earthquake hazards - what are L waves

Answer 3

• love waves
• surface wave
• slowest
• cause side to side motion
• larger energy is focussed on the surface
• most damaging

Question 4

earthquake hazards - liquefaction

Answer 4

• pore spaces in loosely packed, saturated soils fill up with water
• ground shaking due to the earthquake causes increased water pressure
• this causes the ground to behave like a liquid
• the upwelling of liquid soil moves downslope
• unsupported foundations can sink and buildings collapse

Question 5

earthquake hazards - crustal fracturing and ground shaking

Answer 5

• a locked fault is where there hasn’t been movement at the boundary for a long time
• tectonic strain builds up as plates try to move and elastic energy is stored in the rock
• eventually pressure exceeds strength and is released causing crustal fracturing
• energy is released as seismic waves
• these radiate from the hypocentre and are experienced as ground shaking

Question 6

earthquakes - what are the parts

Answer 6

• a fault is a crack in the crust
• the hypocentre is the point within the crust where the earthquake starts
• the epicentre is the point on the surface directly above the hypocentre, where intensity is greatest
• the focal depth is the distance between the hypocentre and epicentre

Question 7

what are primary hazards of an earthquake

Answer 7

• ground shaking
• crustal fracturing

Question 8

what are secondary hazards of earthquakes

Answer 8

• landslides and avalanches
• liquefaction
• tsunamis and flooding

Question 9

what are the primary hazards of volcanoes

Answer 9

• pyroclastic flow
• lava flow
• tephra
• volcanic gases

Question 10

volcanic primary hazards - what is pyroclastic flow

Answer 10

• mixture of tephra and poisonous gas
• up to 1000 degrees C
• can move at 700km/h
• happens at composite volcanoes

Question 11

volcanic primary hazards - what is lava

Answer 11

• magma at the surface
• basaltic is less viscos so travels faster, comes with gentle eruptions
• andesitic is slower and more viscous, comes with more explosive eruptions
• rhyolitic is extremely viscos and comes with the most explosive eruptions

Question 12

volcanic primary hazards - what is tephra

Answer 12

• rock fragments ejected into the air
• ash can cause roofs to collapse / damage electronics / cause breathing issues etc

Question 13

volcanic primary hazards - what is volcanic gas

Answer 13

• predominantly water vapour
• causes heavy rain or lahars
• sulphur dioxide is released and reflects and reflects solar radiation which cools the earth
• can lead to acid rain
• some gases are poisonous eg fluorine

Question 14

volcanic secondary hazards - what are lahars

Answer 14

• water mixed with debris flowing rapidly along valleys
• very fast and carries heavy load (boulders)
• can travel up to 60km/h

Question 15

volcanic secondary hazards - what are jökulhlaups

Answer 15

• floods of meltwater underneath an icecap / glacier
• leads to formation of lake when water causes ice to melt
• extremely strong flow of water that can wash away infrastructure like bridges

Question 16

what causes a tsunami

Answer 16

• oceanic plate subducts under continental at convergent boundary
• friction due to elastic energy and tectonic strain builds up in the Benioff zone or at a locked fault
• it is releases causing an upthrust of the plate
• water above the boundary is displaced, forming a wave