Geophysical Hazards - Part 1: Plate Movement Flashcards
Describe Characteristics of the Crust to the Inner Core
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.
Explain convection currents in the mantle. (6 steps)
- Heating occurs between the inner core to the mantle.
- Denser, cooler magma in the lower mantle heats and rises making it less dense.
- When it reaches the crust it’s forced to move in opposite directions.
- The movement causes cooling making the liquid rock sinks back down towards the core.
- The friction between the convection current and the crust causes the tectonic plates to move.
- The direction of movement of tectonic plates is determined by which way the convection currents are flowing.
What are earthquakes? (4 features)
- Series of seismic vibrations or shock waves originating from the focus.
- Epicenter = point on surface above the focus.
- Foreshocks and aftershocks.
- Seismic waves can travel along surface or through the body.
Convergent/Collision/Destructive plate boundary.
Continental-Continental and Oceanic-Continental
Continental-Continental:
- Two continental plates move towards each-other.
- Little subduction due to low density rock.
- Rock gets folded, faulted, thickened.
- 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:
- Oceanic plate subducts continental
- Volcanic arcs arise
- Oceanic = densert = high subduction potential
- Volcanoes eurpt
Example: Cascade mountains of Western North America // The Andes of Western South Africa
Divergent/constructive plate boundaries:
Oceanic and Continental
Oceanic:
- Tectonic plates are pulled apart
- Slab pull is created when plates SINK into the MANTLE at SUBDUCTION zones.
- Convection currents lift crust
Example: Mid-Atlantic Ridge:
- Fissure eruptions
- Shallow earthquake activity
- New sea floor + widen ocean basin
Continental:
- Pull is not strong enough.
- Currents cause plates to arch upwards
- Plates are pulled thin and fractured into rift-shape
- Faults develop + central rock slides.
- Earthquakes can occur
Example: East Africa Rift Valley or the Dead Sea
Conservative/Passive/Transform
Oceanic and continental
- Horizontal movement only.
- Plates move past each other, rubbing along the edges.
Oceanic:
- Short faults on the sea floor near mid-ocean ridges.
- Plates split at different speeds.
- Space is created between margins
- Once the oceanic plate spreads beyond overlap, a fracture zone extends across seafloor.
Continental:
- Extra forces (compression + extension) create mountainous welts and down-dropped valleys.
- Thick crust = wide deformation zones.
Example: San Andreas, California = 100km of faults.
P versus S waves
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.
Love vs Rayleigh waves
Both travel at slow speeds, both travel through solids on the crust.
L waves = horizontal shake.
R waves = vertical shake.
4 Human causes of earthquakes
Construction of large dams, mining, hydraulic fracturing, testing nuclear weapons.
How do we measure earthquakes?
Richter scale: seismometer produces seismograph. Numbered 1-10 and is logarithmic.
6 Primary Earthquake Hazards
Shaking Ground ruptures Landslides Collapsed buildings Gas and water lines burst Fissures in roads
8 Secondary Earthquake Hazards
Aftershocks Fires Water-borne diseases Road blockage Floods Tsunamis Soil liquefaction
7 Factors effecting severity of earthquake impacts
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
Factors for predicting future earthquakes
Time since last large earthquake, the longer ago the more likely it is.
Earthquake patterns
Mathematical models
Outline the year, location, plates, boundary, epicenter, focus, magnitude of the Christ Church Earthquake
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
Outline the primary impacts of the christ church earthquake
185 killed. 2000 injured. Hundreds km water pipes and swer pipes damages. 50% infrastructure damaged. Liquefaction. Glacier broke creating iceberg. 80% city lost electrics.
Outline the secondary impacts of the Christ Church earthquake
Businesses out of action, loss of jobs + income Schools sharing classrooms Hard to travel on roads Mental health Loss of tourism - closing Rugby pitch
Outline the short term responses of the Christ Church earthquake
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.
Outline the Long term responses to the Christ Church earthquake
898 million dollars in building claims.
Temporary housing and made damaged houses watertight.
Water and sewage restored by August.
Outline the year, location, plates, boundary, epicenter, focus, magnitude of the Haiti earthquake
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
Outline the short term impacts of the Haiti earthquake
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.
Outline the long term impacts of the Haiti earthquake
Destroyed businessed Rebuilding infrastructure over years People still in temp. accommodation Diseases Need long-term strategy
Outline the primary responses to the Haiti earthquake
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.
Outline the secondary responses to the Haiti earthquake
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.
Outline 3 differences between the two earthquakes.
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.
What are key features of volcanoes from bottom to top?
Magma chamber Magma Vents Crater Lava Volcanic bombs Ash, steam and gas
Describe the 3 types of volcanoes
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.
What primary hazards are caused by volcanic eruptions
Pyroclastic flows and surges Lahars Collapse: Avalanches Lava flows Tsunamis
Outline how a volcano forms in 6 steps + which plate boundaries
- magma reaches earth surface
- lava spews from vent
- lava cools
- volcano erupts again
- lava cools on top of solid lava
- process repeats
DIVERGENT and CONVERGENT
2 types of volcano names + main difference
Lava creeps slowly and burns everything
Pyroclastic is faster (80-400km/h) and more explosive
Outline the Montserrat volcanic eruption year, location, plate boundary
Year: July 18 1995
Location: Small island in Caribbean
Define Risk, Vulnerability and Hazard Perception
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.
Define resilience and adaptation
RESILIENCE: The ability to protect lives, jobs and infrastructure + ability to recover
ADAPTATION: Ways that human activities are altered due to increased hazard risk.
Outline the primary hazards of the Montserrat eruption
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
Outline the secondary hazards of the Montserrat eruption
23 deaths
Over 100 injured
Displaced people - 50 sharing toilet, sewage tanks not emptied for weeks, water diseases spread e.g. cholera.
Outline the primary responses
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.
Outline the secondary responses
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
