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IB Geography - Geophysical Hazards
Terms in this set (76)
crust, mantle, outer core, inner core
Very thin and rigid. Continental crust is thicker but less dense. oceanic crust is thinner, more dense and older.
Semi-molten rock, flows very slowly (82% of Earth's volume)
Very dense, liquid
Very dense, solid - made of iron and nickel
Two flows of heat from earth's interior to the surface
- Primordial heat
Heat produced from the radioactive decay of materials in the mantle and crust
Heat lost by the earth as it continues to cool from its original formation
Occurs in the mantle. Heat from the core heats magma, making it rise. As it rises, it cools and becomes denser, therefore it sinks. The friction of the moving magma with the surface of the earth causes tectonic plates to move. This process repeats.
Subduction/destructive plate boundary
The plunging of one plate below another. Subduction zones normally occur when oceanic crust (thinner but more dense) and contintental (thicker) crust collide. The oceanic crust submerges.
Mountains, volcanoes, earthquakes
Occurs at constructive plate boundaries. Upwelling convection in the mantle causes the crust to form a ridge. Tension develops causing the lithosphere to stretch and crack. The central block moves downwards and magma rises through the faults and forms new crust. This process repeats as convection currents continue.
Can form mountain ranges.
Constructive plate boundary
Plates that move away from each other. Magma rises through gap and forms new crust as it cools.
Conservative plate boundary
Where two tectonic plates slide past each other (can be in the same or different direction).
What happens when continental crust collides?
The crust buckles up and forms fold mountains. Compression and high pressure of sediment over many years also form these.
A tall, steep-sided mountain in which layers of lava alternate with layers of ash and other volcanic materials. Formed by alternate eruptions of lava followed by eruptions of fragmental material.
Chimborazo in Mexico
Have gently sloping sides, a shallow crater and large circumference. Formed from very hot, runny basaltic lava - no explosive activity
Mauna Loa in Haiwii
Steep volcano with concave crater and central vent. Built up from ashes, cinders, and rocks (solid material) that burst from Earth during a violent eruption.
Cinder Cone in Northern Carolina
Scalding avalanche of ash and hot, toxic expanding gas, traveling very fast down the side of a volcano
Icelandic lava eruptions
Persistent fissure (linear volcanic vent) eruption. Large quantities may build up vast horizontal plains
Hawaiian lava eruption
Involve a central vent. Runny basaltic lava runs down the sides of the volcano.
Explosive reaction that produce pyroclastic rock. White cloud forms and large quantites of lava are blasted out.
Occur when the pressure of trapped gases in magma becomes sufficient to blow off overlying crust of solidified lava. Releases large quanities of ash into the atmosphere.
Primary hazards associated with volcanoes
- Lava flows
- Ash fallout
- Pyroclastic flows
- Gas emissions
Secondary hazards associated with volcanoes
- Mudflows/lahars (when ash joins with rainwater)
- Landslides (debris avalanches) as the land becomes unstable
A series of seismic vibrations which originate from the focus
What is the focus?
The point at which the plates release their tension
the point on the Earth's surface directly above the focus of an earthquake
Primary (P) waves
Waves are parallel to the direction of travel. Faster than S waves and can move through both solids and liquids
Secondary (S waves)
Waves are perpendicular to the direction of travel. Unable to move through liquids.
A type of seismic wave that forms when P waves and S waves reach Earth's surface. Consist of Love waves and Raleigh waves
Moves ground side to side. Travel faster than Raleigh waves
Moves ground up and down
What are earthquakes caused by other than plate boundaries?
Construction of large dams, mining, testing of nuclear weapons
Primary hazards of earthquakes
Secondary hazards of earthquakes
Soil liquefaction, landslides, rockfalls. mudflows, tsunamis
The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud. Occurs in saturated soils
How does liquefaction occur?
In saturated soils, the gaps between water particles are filled with water. When the soil particles are vibrated, they lose contact with each other and act like a liquid.
Large-scale movement of the Earth's surface that are not accompanied by a moving agent such as a river
Examples of mass movement
Creep, landslides, mudflows, solifluction, debris avalanche
Slow, downslope flow of water-saturated materials common to permafrost areas. Continuous melting and freezing.
Factors increasing shear stress
- Removal of support through slope steepening and undercutting e.g through water erosion
- Increased weight on slope e.g accumulation of debris
Factors reducing shear strength
- Weathering effects - makes rocks/ground weaker
- creation of fissures and cracks
- Organic effects e.g burrowing of animals, decay of roots
Global distribution of earthquakes
- most occur near plate boundaries e.g near the mid-atlantic ridge
- many around the edge of the pacific ocean
- broad belts = subduction zones and collision boundaries
- narrow belts = constructive and conservative
Global distribution of volcanoes
- most occur at place boundaries
- some occur at hotspots e.g in Hawaii
- 75% of historically active volcanoes in Pacific Ring of Fire
a plume of hot material rising from the mantle
Global distribution of landslides
common in areas that have:
- high seismic activity i.e earthquakes
- high rainfall, especially high short term intensities
- high population density
most fatal landslides happen in low income counties - mostly parts in Asia
the expected frequency of an event
Measures the magnitude of the earthquake. The scale is logarithmic.
Volcanic explosive index
Measures the strength of a volcano. Based on the amount of material ejected in the explosion, the height of clouds and the amount of damage caused
the conditions that increase the susceptibility of a community to a hazard
Economic factors affecting vulnerability
- Levels of wealth and development
- Building styles
- Access to technology
- Insurance cover
Social factors affecting vulnerability
- Public education/ educational programmes
- Awareness of hazards
- Gender (women and children more vulnerable)
Demographic factors affecting vulnerability
- Population density
Political factors affecting vulnerability
- Effectiveness of management and planning
- Effectiveness of lines of communication
Geographic factors affecting impacts of geophysical events
- magnitude and frequency of events
- How close the earthquake is to the surface
- Time of day
- Distance from the event
- Types of rocks and sediments
- Secondary hazards
The likelihood of loss of life, injury, destruction and damage from a disaster
Factors affecting perception of risk
- Material well-being
A description of a specific type of local hazard
Ways to characterise hazards (hazard profiles)
- Recurrence interval
- Areal extent
- Spatial concentration
- Speed of onset
Trends in geophysical hazards
- Geophysical hazards have remained constant from 1994 to 2013
- Earthquakes and Tsunamis have killed the most people
- Most natural disasters have occurred in Asia
- Low income countries disproportionately affected
Population growth and natural disasters
Urbanization in seismic zones have increased significantly - increased vulnerability. Occuring mostly in poorer regions - death rates are higher
- ground surface changes
- Ground tilt
- Changes in rock stress
- Micro-earthquake activity (measured using seismometers)
- Seismometers to record mini earthquakes as magmas rises
- chemical sensors to measure increased sulphur levels
- Physical swelling of volcano
- Change in animal behaviour
- Land-use zoning
- New technology
Regulation of how land in an area may be used. Some land-uses may be prevented in at risk areas e.g. near a fault line
Protection against possible financial loss - however most LIC residents cannot afford insurance. Some people may not think its worthy to spend on an event that might not happen.
Can be used to record the swelling of volcanoes and measure changes in the ground. Warnings can then be given out. Mobile phones can be used to inform agencies about changes and apps that notify people.
- Terracing steep slopes
- Drainage of water from slopes
- Erosion control at cliff bases
- Restraining structures e.g. stone walls
Managing earthquake risk
Buildings can be designed to withstand earthquakes
- Single story buildings reduce swaying
- Tall buildings built with soft story (upper floors sink into it and cushion impact)
- Mounting the foundations on rubber (allows movement and isolates building from tremor)
- Steel constructed frames
- Shock absorbers e.g. tyres
- Reinforcing walls e.g. bamboo
Managing volcano risk
- Dry channels to divert lava flows
- Evacuating area
Managing tsunami risk
- Sea walls
- Early warning systems
Disaster recovery model
Rescue, rehabilitation, reconstruction
In the immediate aftermath, people are searched for using thermal sensors and sniffer dogs. Emergency aid given and rubble is cleared.
People being able to make their homes safe and live in them again. Restoration of major services. Takes longer in LICs
If rehabilitation is not possible, reconstruction is necessary. This can take years. Takes longer in LICs
Use of mobile phones in geophysical hazards
Information can be spread quickly, apps such as RapidFTR have been made to reunite children with their parents in disaster situations, information about missing people can be recorded
However, not everyone has access to mobile phones i.e. in poorest LICs
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