Geophysical Hazards - Part 1: Plate Movement Flashcards

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1
Q

Describe Characteristics of the Crust to the Inner Core

A

Crust - brittle, low density materials. Oceanic = 5km
Land = 30km

Mantle - 2900km
Molten rock causes tectonic movement

Core - Highest density. Combined thickness 3500km.

Outer core - liquid nickel and iron at 4000-5000 degrees Celsius.
2300km.

Inner core - solid nickel and iron 5000-7000 degrees and 1200km.

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2
Q

Explain convection currents in the mantle. (6 steps)

A
  1. Heating occurs between the inner core to the mantle.
  2. Denser, cooler magma in the lower mantle heats and rises making it less dense.
  3. When it reaches the crust it’s forced to move in opposite directions.
  4. The movement causes cooling making the liquid rock sinks back down towards the core.
  5. The friction between the convection current and the crust causes the tectonic plates to move.
  6. The direction of movement of tectonic plates is determined by which way the convection currents are flowing.
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3
Q

What are earthquakes? (4 features)

A
  1. Series of seismic vibrations or shock waves originating from the focus.
  2. Epicenter = point on surface above the focus.
  3. Foreshocks and aftershocks.
  4. Seismic waves can travel along surface or through the body.
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4
Q

Convergent/Collision/Destructive plate boundary.

Continental-Continental and Oceanic-Continental

A

Continental-Continental:

  1. Two continental plates move towards each-other.
  2. Little subduction due to low density rock.
  3. Rock gets folded, faulted, thickened.
  4. Magma cannot penetrate thick crust –> forms granite.

Example: The Himalayas and the Tibetan Plateau = 50 mill. yrs of collision between Indian-Eurasian plates.

Oceanic-Continental:

  1. Oceanic plate subducts continental
  2. Volcanic arcs arise
  3. Oceanic = densert = high subduction potential
  4. Volcanoes eurpt

Example: Cascade mountains of Western North America // The Andes of Western South Africa

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5
Q

Divergent/constructive plate boundaries:

Oceanic and Continental

A

Oceanic:

  1. Tectonic plates are pulled apart
  2. Slab pull is created when plates SINK into the MANTLE at SUBDUCTION zones.
  3. Convection currents lift crust

Example: Mid-Atlantic Ridge:

  • Fissure eruptions
  • Shallow earthquake activity
  • New sea floor + widen ocean basin

Continental:

  1. Pull is not strong enough.
  2. Currents cause plates to arch upwards
  3. Plates are pulled thin and fractured into rift-shape
  4. Faults develop + central rock slides.
  5. Earthquakes can occur

Example: East Africa Rift Valley or the Dead Sea

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6
Q

Conservative/Passive/Transform

Oceanic and continental

A
  1. Horizontal movement only.
  2. Plates move past each other, rubbing along the edges.

Oceanic:

  1. Short faults on the sea floor near mid-ocean ridges.
  2. Plates split at different speeds.
  3. Space is created between margins
  4. Once the oceanic plate spreads beyond overlap, a fracture zone extends across seafloor.

Continental:

  1. Extra forces (compression + extension) create mountainous welts and down-dropped valleys.
  2. Thick crust = wide deformation zones.

Example: San Andreas, California = 100km of faults.

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7
Q

P versus S waves

A

P waves can travel at 6km/sec, travel through solids and liquids, and shake vertically.

S waves can travel at 4km/sec, travel through solids and shake horizontally.

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8
Q

Love vs Rayleigh waves

A

Both travel at slow speeds, both travel through solids on the crust.
L waves = horizontal shake.
R waves = vertical shake.

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9
Q

4 Human causes of earthquakes

A

Construction of large dams, mining, hydraulic fracturing, testing nuclear weapons.

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10
Q

How do we measure earthquakes?

A

Richter scale: seismometer produces seismograph. Numbered 1-10 and is logarithmic.

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11
Q

6 Primary Earthquake Hazards

A
Shaking
Ground ruptures
Landslides
Collapsed buildings
Gas and water lines burst
Fissures in roads
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12
Q

8 Secondary Earthquake Hazards

A
Aftershocks
Fires
Water-borne diseases
Road blockage
Floods
Tsunamis
Soil liquefaction
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13
Q

7 Factors effecting severity of earthquake impacts

A
Magnitude and frequency
Pop. density and distribution
Type of buildings and ifrastructure
Time of day
Distance from epicentre
Types of rock and sediment (urbanisation, deforestation)
Economic development
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14
Q

Factors for predicting future earthquakes

A

Time since last large earthquake, the longer ago the more likely it is.
Earthquake patterns
Mathematical models

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15
Q

Outline the year, location, plates, boundary, epicenter, focus, magnitude of the Christ Church Earthquake

A

Year: 22 Feb 2011
Location: Pacific Ocean on the Oceania Plate.

Tectonic plates: Australian and Pacific

Boundary: Conservative

Epicenter: 6 miles southeast of CC.

Focus: shallow, 3.1 miles.

Magnitude: 6.3

Aftershock: from 2010 earthquke

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16
Q

Outline the primary impacts of the christ church earthquake

A
185 killed. 
2000 injured.
Hundreds km water pipes and swer pipes damages.
50% infrastructure damaged.
Liquefaction.
Glacier broke creating iceberg.
80% city lost electrics.
17
Q

Outline the secondary impacts of the Christ Church earthquake

A
Businesses out of action, loss of jobs + income
Schools sharing classrooms
Hard to travel on roads
Mental health
Loss of tourism - closing Rugby pitch
18
Q

Outline the short term responses of the Christ Church earthquake

A

Most vulnerable cared for.
Chemical toilets for 30k people
Areas classified by most damaged and costly.
International aid worked cleared roads. 80% cleared by August.

19
Q

Outline the Long term responses to the Christ Church earthquake

A

898 million dollars in building claims.
Temporary housing and made damaged houses watertight.
Water and sewage restored by August.

20
Q

Outline the year, location, plates, boundary, epicenter, focus, magnitude of the Haiti earthquake

A

Year: Jan 12 2010

Plate boundary: Island of Hispaniola sits on the Gonave microplate between North American and Caribbean.

Epicenter location: 25km west of port-au-prince.

Focus: 13km below surface.

Aftershocks occurred.

Magnitude: 7

21
Q

Outline the short term impacts of the Haiti earthquake

A
300k injured + 230k dead.
Hospitals collapsed.
30k commercial buildings collapsed.
Crippled main airport + ports and paved roads.
300k homes damaged.
Communication infrastructure damaged.
Crowded camps.
22
Q

Outline the long term impacts of the Haiti earthquake

A
Destroyed businessed
Rebuilding infrastructure over years
People still in temp. accommodation
Diseases
Need long-term strategy
23
Q

Outline the primary responses to the Haiti earthquake

A

Dominican republic provided water and medical supplies.
Rescue teams from many countries.
GIS used to provide satellite images of area to assist aid.
UN troops and police sent.
UN delivered food to 200k people.

24
Q

Outline the secondary responses to the Haiti earthquake

A

1,300 camps built after 1 year.
Schools being rebuilt.
Small farmers supported.
Money pledged by orgs. and govs. to help rebuilding but slow progress.
Programs paying Haitians to clear rubble.

25
Q

Outline 3 differences between the two earthquakes.

A

The response in Christchurch was more efficient. A full emergency management programme was in place within 2 hrs.

Christchurch had a smaller magnitude but was closer to epicenter = more damage.

Lower deaths in Christchurch.

26
Q

What are key features of volcanoes from bottom to top?

A
Magma chamber
Magma
Vents
Crater
Lava
Volcanic bombs
Ash, steam and gas
27
Q

Describe the 3 types of volcanoes

A

Composite - most common, alternating eruptions of fragmental material, several vents

Cinder cone - violent eruptions, formed by fragments of solid material, concave shape.

Shield - no explosive activity, formed by hot, basaltic lava, sloping sides, shallow crater, large circumference.

28
Q

What primary hazards are caused by volcanic eruptions

A
Pyroclastic flows and surges
Lahars
Collapse: Avalanches
Lava flows
Tsunamis
29
Q

Outline how a volcano forms in 6 steps + which plate boundaries

A
  1. magma reaches earth surface
  2. lava spews from vent
  3. lava cools
  4. volcano erupts again
  5. lava cools on top of solid lava
  6. process repeats

DIVERGENT and CONVERGENT

30
Q

2 types of volcano names + main difference

A

Lava creeps slowly and burns everything

Pyroclastic is faster (80-400km/h) and more explosive

31
Q

Outline the Montserrat volcanic eruption year, location, plate boundary

A

Year: July 18 1995

Location: Small island in Caribbean

32
Q

Define Risk, Vulnerability and Hazard Perception

A

RISK: Probability of a hazard causing harm

VULNERABILITY: geographic conditions that increase susceptibility to a hazard and its impacts.

PERCEPTION: Degree of threat of a hazard to different people.

33
Q

Define resilience and adaptation

A

RESILIENCE: The ability to protect lives, jobs and infrastructure + ability to recover

ADAPTATION: Ways that human activities are altered due to increased hazard risk.

34
Q

Outline the primary hazards of the Montserrat eruption

A
Clouds of ash and steam.
The 1996 eruption caused mud flows and lava flows. Dome collapsed + boiling rocks and ash thrown out, new dome created. 
75% island covered in ash
Destroyed infrastructure
Airport and port closed
35
Q

Outline the secondary hazards of the Montserrat eruption

A

23 deaths
Over 100 injured
Displaced people - 50 sharing toilet, sewage tanks not emptied for weeks, water diseases spread e.g. cholera.

36
Q

Outline the primary responses

A

Public services moved north.
Southern third of island = evacuated.
5k evacuated to safe zone created in Salem and Plymouth.
UK provided 41 million gbp in relief and recovery. Royal Navy sent ships to evac. 4k people to Antigua.
Plymouth most impacted. Pop. of 4000.
Between 1995-2000, 2/3 of the population was forced to flee to UK.
1997 - 1,200 people
2016 - 5k people

NGO’s Int. Red Cross = organised evac camps.

37
Q

Outline the secondary responses

A

1997 - Islanders offered 2,500 each to relocate to UK
UK gave 75 million gbp to help long-term development.
Rebuilding homes and vital infrastructure takes long time.
Respiratory diseases.
Implemented seismic monitoring at Montserrat Volcano Observatory.
Skills shortage due to emigration
1995 - 12k people
1997 - 1,200 people
2016 - 5k people