Tectonics Pack B

Question 1

What is the global distribution of tectonic hazards?

Answer 1

• Earthquakes are located in long, narrow belts along all types of plate boundaries
• Volcanoes and earthquake activity occur in similar places in narrow zones of activity (e.g. Mid-Atlantic Ridge and Pacific Ring of Fire)
• Hotspots are small areas away from plate margins with an unusually high heat flow linked to volcanic activity

Question 2

What are the characteristics of earthquakes along different plate boundaries?

Answer 2

• Divergent margins = shallow and related to volcanic activity
• Oceanic crust subduction zones = frequent powerful earthquakes that might create tsunamis
• Collision margins = shallow but powerful/hazardous if humans inhabit area
• Some occur away from margins due to stress creating movement along old fault lines
• Human activity like fracking can cause minor earthquakes

Question 3

What are the statistics for earthquake and volcano distribution?

Answer 3

• 450 of world’s volcanoes (active and dormant) and 90% of earthquakes are located in Pacific Ring of Fire
• 80% of active volcanoes are at subduction zones
• 75% of magma reaching the surface happens at divergent boundaries

Question 4

What are the characteristics of volcanoes at different boundaries?

Answer 4

• Divergent = non-violent, in the deep ocean, little hazard except where inhabited land is crossed
• Convergent = violent, hazardous (e.g. Mt St Helens)

Question 5

What is the hotspot theory?

Answer 5

• There are fixed spots in the mantle where magma rises to the surface
• Eruptions are usually not very violent but produce large quantities of lava

Question 6

How do hotspots form?

Answer 6

• A plume of magma rises from the asthenosphere
• Magma pushes through the crust to form volcanoes at the surface
• Form a chain of volcanoes as plate moves over hotspot
• The line of volcanoes move with the plate
• Oceanic volcanoes cool and subside as islands or sea mounts
• Continental volcanoes become extinct
  E.g. Hawaiian Islands extending 2400km
  E.g. Yellowstone (continental)

Question 7

What is an alternative theory to the hotspot theory?

Answer 7

• Plates have weaknesses from former collisions or are stretched by slab oull
• When the weak sections pass over previously subducted material, the molten rock can move to the surface

Question 8

What physical factors does the impact of a tectonic hazard depend on?

Answer 8

• Magnitude
• Spatial predictability
• Duration
• Areal extent
• Speed of onset
• Frequency

Question 9

What are the human factors that influence the impact of a tectonic hazard?

Answer 9

• Population density
• Level of development
• Vulnerability of the population

Question 10

What is a hazard profile?

Answer 10

Only looks at physical factors of a hazardous event

Question 11

What are the uses of hazard profiles?

Answer 11

• Understand and compare the physical characteristics and processes of the different types of tectonic hazard
• Compare the same type of hazard in different locations and at different times
• Valuable to decision makers who are involved in the day to day management of hazards

Question 12

How does spatial predictability influence impact?

Answer 12

• An area that has never had an event will experience greater impacts
• More people and places will be unprepared
• Accurate prediction allows for evacuation of danger zones
• Too many inaccurate predictions mean people start to ignore warnings

Question 13

How can earthquakes be predicted?

Answer 13

• No characteristic pattern of change or seismic activity that indicates EQs
• Possibilites are radon gas, water table changes, magnetic field variations and animal behaviour changes
• Seismic gap theory suggests all parts of a fault line must move the same over a given time period so this may be useful to predict for places that have had a gap in seismic acitivity

Question 14

How can volcanoes be predicted?

Answer 14

• Changes in gas emissions
• Ground deformation
• Hydrology
• Temperature changes
• Seismic activity
• Not accurate in terms on magnitude

Question 15

How does areal extent influence impact?

Answer 15

• The larger the area affected, the greater the potential impact
• More people and places will be affected
• Local -> regional = shield volcano, composite volcano, subduction zone earthquake, tsunami

Question 16

How does frequency influence impact?

Answer 16

• Events that occur more often are likely to create cumulative impacts
• Reduces time to recover
• Although, rare events have more energy

Question 17

How does magnitude influence impact?

Answer 17

• The greater the amount of energy released, the greater the impacts
• The most important factor
• It is the size of the physical force of a hazard event

Question 18

What is the magnitude scale for volcanic eruptions?

Answer 18

• VEI
• 0 to 8 but no actual upper limit
• 10 fold increase each time
• Looks at volume of material in eruption, height of ash cloud, direction of eruption and observations
• No account of material density or SO2 emissions

Question 19

What are the scales to measure earthquake magnitude?

Answer 19

• Richter scale
• Moment magnitude scale
• Mercalli scale

Question 20

What is the Richter scale?

Answer 20

• 1 to 10
• Uses the amplitude of the largest wave recorded
• Old

Question 21

What is the Moment Magnitude scale?

Answer 21

• 1 to 10
• Looks at area of fault rupture and amount of fault movement = amount go energy released

Question 22

What is the Mercalli scale?

Answer 22

• I to XII
• Amount of dmage caused by surface shaking
• Descriptive scale

Question 23

How does speed of onset influence impact?

Answer 23

• The faster the event, the greater the impact
• Shorter warning time so places will be unprepared and will not have evacuatd
• Looks at how quickly the peak of the hazard event arrives
• EQs are instant so there is no warning time

Question 24

How does duration influence impact?

Answer 24

• Longer an event lasts, the greater the impacts
• Aftershocks and tsunamis may follow an EQ
• Secondary hazards may follow an eruption (e.g. lahars)

Question 25

How do hazard profiles help for recovery?

Answer 25

- Created after an event - Record characteristics to help planners in future - Retrofitting