Hazards

Question 1

What are the 3 main layers of the Earth’s structure?

Answer 1

Crust, Mantle, Core

Question 2

Describe the 2 types of crust

Answer 2

Continental - much thicker (av. 35km) but less dense, mainly granitic
Oceanic - Denser but not as thick (5-10km) - mainly basaltic

Question 3

Describe the parts of the mantle

Answer 3

Lithosphere - crust to 100km (rigid layer)
Asthenosphere - semi molten layer - lubricating layer over which tectonic plates slide - convection currents operate here
Mesosphere - solid material

Question 4

Describe the parts of the core

Answer 4

Outer core - liquid
Inner core - solid - hotter but under so much pressure that becomes solid
Iron and nickel

Question 5

What was Alfred Wegener’s theory and what was the supercontinent called?

Answer 5

Continental drift - continents slowly drifted about the Earth’s surface
Pangaea

Question 6

What is the geological evidence for continental drift?

Answer 6

Shapes of continents fit together - e.g. Eastern side of South America and Western side of Africa
Mountain chains and glacial valleys on either side of oceans that show great similarity and used to be part of a single ting

Question 7

What is the biological evidence for continental drift?

Answer 7

Similar fossil reptiles found in South America and South Africa
Younger rocks show less similarity in fossils - different evolutionary paths and speciation after physical barrier (ocean) introduced
Fossils of organisms found in tropical climates found in temperate or even polar climates

Question 8

Describe paleomagnetism and sea-floor spreading

Answer 8

As lava cools, particles of magnetic minerals become orientated in the direction of the Earth’s magnetic field - reverses around every 20,000 years
Strips of rock with same magnetic orientation occur symmetrically either side of mid-ocean ridges - sea-floor spreading occurs as molten material rises up to the ocean bed and pushes older rock away from the ridge (divergent plate)
Thickest and oldest sediments near continents, younger deposits further out in the oceans

Question 9

What is the definition of sea-floor spreading?

Answer 9

The lateral movement of new oceanic crust away from a mid-ocean ridges

Question 10

How are rift valleys formed?

Answer 10

Magma rising at divergent plate boundaries forces rigid lithosphere and crustal rocks into a dome - enormous stresses created as dome rises results in rocks fracturing - sinking down of rocks between fractures or faults

Question 11

What has been formed in the north Atlantic by vast amounts of magma production at a mid-oceanic ridge?

Answer 11

The volcanic island of Iceland - rift valley between north American and Eurasian plates

Question 12

Where is most material along divergent boundaries erupted?

Answer 12

Underwater - lava cools rapidly as it meets sea water - rounded mounds of lava called pillow lavas

Question 13

What are black smokers and what is found where they occur?

Answer 13

Superheated sea water that has seeped into magmatic rocks rising in jets containing minerals from the ocean bed
Unique and highly specialised organisms and ecosystems exist at these locations

Question 14

What are transform faults?

Answer 14

When ocean ridges are displaced sideways and broken into segments - earthquakes

Question 15

What is graben?

Answer 15

Downfaulted section of a rift valley

Question 16

Where can rifting and doming occur away from mid-ocean ridges?

Answer 16

Where the crust thins - e.g. between Egypt and Turkey - rift valley, graben. Sometimes sinks below sea level, e.g. Dead sea, Israel

Question 17

Oceanic-continental convergent plate boundaries

Answer 17

Oceanic subducts beneath continental due to higher density - forms deep ocean trench
Benioff zone - fracturing and faulting releases seismic energy
Descending plate melts and molten material is less dense than surroundings so rises towards surface - volcanic eruptions
Sediments carried by oceanic plates subducted or crumpled up along with leading edge of continent to form mountain chains, e.g Andes

Question 18

Oceanic-oceanic plate boundaries

Answer 18

Slghtly denser plate subducted, forming ocean trench, magma rises, erupting as a chain of volcanoes known as an island arc.

Question 19

Continental-continental

Answer 19

Little subduction - grind together, releasing much seismic energy. Rocks compressed and extensive fold mountain ranges form, e.g Himalayas

Question 20

Describe conservative plate boundaries

Answer 20

Plates slide past each other - no subduction so no volcanic activity - frictional resistance and build up of pressure results in earthquakes and seismic actvity
e.g. san andreas fault
Can be ‘tear’ showing where plates have moved relative to each other

Question 21

What factors influence the type of volcanic activity occurirng at any one location?

Answer 21

Type of plate boundary
Chemistry of the lava and its viscosity (how well it flows)
Materials erupted (ash, pumice, lava)
Gases produced
How the eruption takes place

Question 22

What are the 2 ways volcanic eruptions can be classified?

Answer 22

Explosive - violent due to build up of pressure within a volcano - tend to have viscous lava such as andesite, which can block the volcano vent - tend to be at convergent plate boundaries - high silica content and acidic - steep sided stratovolcanoes, composite, calderas
Effusive - much less violent due to free-flowing lava such as basalt - tend to be at divergent plate boundaries - low silica content and basic - shield volcanoes, gently sloping sides

Question 23

What is a supervolcano?

Answer 23

A volcano that erupts more than 1000km3 in a single eruption event - tends to exist as a giant caldera - e.g. Yellowstone, Wyoming, USA

Question 24

What are the two key factors involved when measuring and assessing volcanic activity?

Answer 24

Magnitude (amount of material erupted)

Intensity (speed at which material is erupted)

Question 25

What is the logarithmic scale used to measure volcanic explosivity?

Answer 25

Volcanic Explosivity Index (VEI) - scale from 0 (least explosive) to 8 (most explosive)

Question 26

What is an example of a flood basalt (large area of basaltic lava erupted over many hundreds or thousands of years)?

Answer 26

Deccan plateau (500,000km2)

Question 27

Give some examples of volcanic hazards (short term risks)

Answer 27

Primary: Lava flows, pyroclastic flows (500°C, 100km/h), ash fall (breathing difficulties, smothers crops, collapses buildings, disrupts transport), tephra (bombs (>6cm diameter) to fine ash), toxic gases (SO2, CO, CO2, acid rain, death, fun stuff like that)
Secondary: lahars (mud flows can travel at speeds of 50km/h), floods (due to ice melting), tsunamis

Question 28

What is a long-term risk of a major volcanic eruption?

Answer 28

ejecting vast quantities of ash into the upper atmosphere - implications for longer-term climate change due to albedo and blocking of sunlight, cooling climate - Toba (70,000 years ago), has caused global cooling events in the past

Question 29

What do earthquakes result from?

Answer 29

Release of stress and pressure within crustal rocks - possess a focus (point at which waves originate) and an epicentre (location on earth’s surface above focus).

Question 30

What are the 3 types of seismic wave?

Answer 30

Primary (P) - fast travelling, low frequency, longitudinal
Secondary (S) - half speed of P, high frequency, transverse
Surface (L) - slowest of 3, low frequency

Question 31

What are the 3 main ways of assessing earthquake magnitude?

Answer 31

Richter scale - wave amplitude to assess energy released
Modified Mercalli Intensity (MMI) scale - earthquake intensity and impact based on qualitative assessment based upon observation and description
Moment magnitude scale (Mw) - more accurate measure of energy released by an earthquake (amount of physical movement of an earthquake - not useful in low-energy events

Question 32

What are the distinctive hazards generated by earthquakes?

Answer 32

Ground shaking and displacement - horizontal and vertical movement of the grounds. Severity depends on magnitude, distance from epicentre and geology - building collapse, fractured pipelines and sewers, roads and railways break, water supply and irrigation disrupted
Liquefaction - unconsolidated sediments (e.g. sands, alluvium) with high water content behave like a liquid due to earthquake vibrations - riverbanks collapse, structures sink and tilt as their foundations give way
Landslides and avalanches - slopes give way if shaken too much. Deforestation removes binding effect of roots (Nepal). Dams can form from landslide material, leading to flooding
Tsunamis - secondary hazards - underwater earthquakes cause sea bed to rise, displacing large volumes of water, producing very powerful waves with low wave heights and long wavelengths in open water (undetected by ships) - when reach shallow water, wave height can exceed 25m, carrying hundreds of tonnes of water

Question 33

Good quote ;)

Answer 33

Earthquakes don’t kill people, buildings kill people

Question 34

What are the 3 stages of volcanohood?

Answer 34

Active - erupted in past 10,000 years
Dormant - not erupted in past 10,000 years but expected to erupt again in the future
Extinct - not expected to erupt again

Question 35

What is resilience?

Answer 35

Ability to resist, absorb, and recover from shock and stress

Question 36

What is the disaster risk equation?

Answer 36

Risk (R) = Frequency or magnitude of hazard (H) x level of vulnerability (V) / Capacity to cope and adapt (C)

Question 37

What is a disaster?

Answer 37

When a hazard exceeds the capacity of a country, community or household to cope with the effects of that hazard

Question 38

What is the relationship between magnitude and frequency/ recurrence interval?

Answer 38

High energy events occur less frequently (have a longer recurrence interval)

Question 39

Over the past 50 years there has been an increase in the number of tectonic disasters. Why is this not evidence that tectonic activity is rising?

Answer 39

More people are living in seismic zones, consequent increase in building construction and economic activity in the same locations
Emergency Events Database (EM-DAT)

Question 40

What are the stages of the disaster response model?

Answer 40

Pre-disaster (normality)
(Hazardous event occurs - deterioration)
Relief (hours to days) - search, rescue and care - may require national or international outside help
Rehabilitation (days to weeks) - may require national or international outside help - e.g. aid and temporary housing services
Reconstruction (weeks to years) - permanent rebuilding of physical and social infrastructure
(return to normality or even improvement - strategies to modify vulnerability to prevent further disasters)

Question 41

What is the nature of recovery related to?

Answer 41

Need to reduce vulnerability

Need to restore normality as soon as possible

Question 42

What are the 3 groups of strategies to managing tectonic hazards?

Answer 42

Modify the event
Modify people’s losses
Modify people’s vulnerability

Question 43

What is hazard mapping (e.g. predicted lahar routes, ground likely to liquefy) used for?

Answer 43

Land use zoning - prevents building in locations identified by hazard mapping

Question 44

What sort of design do hazard-resistant buildings have?

Answer 44

Aseismic design