Tectonic Hazards Flashcards
1
Q
what are P waves?
A
- fastest wave, first on seismogram
- compression and expansion of waves
- passes through solids, liquids and gasses
2
Q
What are S waves?
A
- transverse waves, sideways movement
- second fastest
- passes through solids but not liquids
3
Q
What are L waves?
A
- Surface waves
- responsible for all the damage
- High amplitude
- slowest type of wave
4
Q
what is the Richter scale?
A
- ranks magnitude from 1-10, measuring the amount of energy released
- works logarithmically (each increase in magnitude is 30x more energy released)
- 0-1 = cannot feel these
- 5 = damage done to weak buildings in epicentre
- 9 = rare but causes unbelievable damage
5
Q
What is the Mercalli scale?
A
- measures from 1-12 in Roman Numerals
- based on observations about the strength of earthquakes in different locations, by damage caused and life lost
- light - felt in doors by many, and outdoors by few
- violent - general panic, very weak constructions collapse
6
Q
What is the Moment Magnitude scale
A
- Updated version of Richter scale
- 32x increase in the amount of energy released between levels
7
Q
what are the primary hazards of earthquakes?
A
- ground shaking
- surface faulting
8
Q
what are the secondary hazards?
A
- Ground failure + liquefaction
- landslides and rockfalls
- Debris flow + mudflow
- Tsunamis
- avalanches
9
Q
What are the impacts of hazards?
A
- loss of life and livelihood
- total/partial destruction of buildings
- interruption of water supplies
- breakage of sewage systems
- loss of public utilities (gas, energy, etc.)
- floods from collapsed dams
- release of hazardous materials
- fires
10
Q
Factors affecting earthquake damage
A
- strength and depth of earthquake and number of aftershocks
- population density
- type of buildings
- time of day
- distance from epicentre
- type of rocks/sediments
- secondary hazards
- economic development
11
Q
what is ground shaking and displacement?
A
- the horizontal and vertical movement of the ground
- settlements close to epicentre and the geology is unconsolidated with a high water content will experience the greatest shaking
- ground movements cause the displacement of rocks along fault lines
12
Q
what is liquefaction?
A
- occurs when waterlogged sediments are agitated by seismic shaking
- separates the grains from each other which reduces the load-baring capacity and acts like a liquid
- can leave large areas covered in a deep layer of mud
13
Q
how do Tsunamis occur?
A
- earthquakes that occur underwater can cause the sea bed to rise, leading to the displacement of water
- when the ocean is deep the waves have a height of less than 1m and have a wide wavelength of up to 200km meaning they can go undetected
- wave height increases rapidly when it approaches shallow water
- water in front of the wave is pulled back out to sea which is called drawdown
14
Q
factors affecting Haiti’s vulnerability to 2010 earthquake
A
- Poor building – houses with no earthquake resistance.
- Poorest country in western hemisphere – 70% on less than $2 a day.
- Life expectancy – 60yrs old
- IMR – 86 per 1000
- GNI - $660 pa
- Long history of unstable governments.
- 86% of people in Port-au Prince lived in slum conditions
- Lack of awareness and coherent emergency plan.
15
Q
Factors affecting Christchurch’s limited vulnerability to earthquakes
A
- Having access to preparation measures:
- hazard mapping
- Education
- Monitoring of seismic activity
- Greater building regulations
- Evacuation orders
- close political ties with other HICs (being member of commonwealth)
16
Q
immediate responses to Boxing day tsunami
A
- fresh water, water purification tablets, food, sheeting and tents came in aid
- medical teams and forensic scientists arrived
- UK government promised £75 million and public donations of £100m followed
17
Q
long term responses to boxing day tsunami
A
- £372m donated by British public a year later - only £128m had been spent by the DEC due to organisational issues
- rebuilding - DEC spent more than £40m on projects in Sri Lanka and Indonesia - plans to spend a further £190m the following year building 20,000 houses
- Indian ocean tsunami warning system set up in 2006 - none previously
18
Q
Earthquake prediction
A
- looking for patterns (relies on there being the same amount of slippage between each dislocation, the rate of deformation within the crust is constant and the friction along the fault line is constant)
- looking for deformation (strain meters, GPS measurements, Microcracks and Radon Gas, major slips)
-
19
Q
Iceland Earthquake management/preparation
A
- education on how to react to earthquakes (DUCK, COVER, HOLD and calling 112, the emergency line)
- security measures - furniture secured to the ground, covering windows, etc.
- civil protection making radio announcements on state radio
- emergency shelters in schools
- Icelandic Meteorological office (IMO) - monitoring, analysing, providing warnings and forecasts - issues public and aviation alerts about impending natural hazards
- uses regularity between earthquakes and devising whether the conditions are right for enough energy to have built up before the next one occurs
- ## Iceland Catastrophe Insurance (ICI) - uses probable maximum loss calculations
20
Q
Iceland earthquake perception of risk?
A
- low due to long term excellent earthquake engineering work as many buildings are seismic resistant
- 2nd highest ranked for education in the world - literacy rate almost 100% meaning people know how to react to earthquakes
- it will be the mindset of the population towards earthquakes which poses the most danger (Icelandic PM)
21
Q
Earthquake monitoring
A
- seismometers - to record micro earthquakes
- magnetometer - to record changes in Earth’s magnetic field
- near-surface seismometers - to record larger shocks
- strainmeters - to monitor surface deformation
- laser survey equipment - to measure surface movement
22
Q
What is a volcano?
A
vent on the earth’s surface through which magma can escape
23
Q
what is magma?
A
A hot, viscous, siliceous melt. containing gases
24
Q
characteristics of an Icelandic fissure volcano
A
- basaltic lava (low in silica)
- low viscosity
- low explosivity
- gases tend to be steam dominated
- erupted at 1200c
- rarely seen on surface
e.g. Hekla
25
characteristics of a Hawaiian Shield eruption
- basaltic lava (low in silica)
- low viscosity
- low explosivity but frequent eruptions
- gases tend to be steam dominated
- erupted at 1200c
- lava can flow for many km's producing huge shallow sided volcanoes
26
Characteristics of a Strombolian eruption
- medium low viscosity
- greater gas content than Hawaiian
- explosions occur at regular intervals following explosion of large gas bubbles
- discharge of streams of incandescent lava into the atmosphere, hundreds of metres high at speeds of 200m/s
- long arcing jets of lava cool and form scoria
27
Characteristics of a Vulcanian eruption
- andesitic lava
- very viscous and contains moderate amounts of gases
- repeated cannon-like explosions of medium - high energy with a discharge of large volcanic bombs `
- no new magma is erupted
- large clouds of gas and cinders
28
characteristics of Pelean eruptions
- explosion of the entire mass of the dome, usually following a large avalanche
- lava domes formed by the extrusion of andesitic and rhyolitic magma
- low in gas
- domes form steep sides which are subject to collapsing in avalanches
- results in the formation of Nuees Ardentes
29
characteristics of a plinian eruption
- high gas content
- high explosivity
- rhyolitic lava
- steep sided
- leads to ash fallout
30
What are the primary/secondary hazards of volcanic eruptions?
Primary:
- lava flows
- pyroclastic deposits
- ash fallout
- gas
Secondary:
- landslides
- mudslides
- rock falls
- lahars
- tsunamis
31
what is a Nuees Ardentes?
the flow of pyroclastic material as well as a cloud of gases that rises from the flow
32
What are Lahars?
- a mixture of flowin water laden with volcanic ash
- very hot
- follows a pre-existing stream/river channel
- high velocity (up to around 40m/s) and thick sediment
- highly destructive
- mount Reiner lahar travelled 60km near Seattle
33
Nevado del Ruiz case study
- volcano erupted causing ice cap to melt releasing between 10 and 60 million cubic metres of water
- led to a lahar being formed
- Armero was 20km away but over 22,000 people died
- 8m deep lahar travelled at 45kph
- civil defence told Armero to evacuate because it was on a previous lahar deposit
- residents refused because it was dark, raining, they had no where to go and they didn't know what it was
- perception of risk was low
34
What is a pyroclastic flow?
- flow of a high-density mix of hot lava locks, pumice, ash and volcanic gas
- travel at very high speeds (faster than 80kph or 50mph)
- rock fragments range from ash to boulders
- very hot (between 200 and 700c)
- most consist of two parts: a lower (basal) flow of coarse fragments that moves along the ground and a turbulent cloud of ash which rises above the basal flow
35
what are the different ways in which a pyroclastic flow is formed?
- collapse of eruption column
- 'boiling over' from eruptive vent
- collapse of lava domes or flows
36
Mount Pelee (Martinique) case study
- erupted on 8th may 1902
- pyroclastic flow formed from dome exploding
- travelled at more than 100mph
- hit st Pierre in 2 minutes
- 30,000 people died - all but one died from suffocating or burning
- major tremors and mudflows that had killed several inhabitants had been ignored
37
secondary hazards of lahars
- eroding, melting and mixing with snow and ice
- damming or blocking streams in volcanic valleys
- increasing the rate of steam runoff and erosion during rainstorms
38
what is ash fallout?
- a mixture of volcanic material, varying in size, ejected from an explosive eruption
- tephra are fragments of rock that are produced when magma or rock is explosively ejected
- ash (<2mm in diameter) is both easily convected upward within the plume and carried downwind for very long distances
- can cause disruption to aviation due to its abrasive nature
- can also impact buildings, transportation, water and wastewater, power supplies, communications equipment, agriculture and primary production
- can cause health impacts to humans and animals
39
how much gas was released in the 1991 mount Pinatubo eruption in a day?
250 megatonnes
40
Dangers of CO2 gas
- breathing air og more than 3% CO2 can lead to headaches, dizziness, increased heart rate and difficulty breathing
- 15%+ can quickly lead to unconsciousness and death
- three ski patrol members where killed at mammoth mountain ski resort after falling into a snow depression surrounding a volcanic fumarole and filled with cool CO2 gas
41
Dangers of Sulfur dioxide (SO2) gas
- irritates skin and the tissues and mucous membranes of the eyes, nose and throat
- can cause acid rain and air pollution downwind of a volcano
- in high concentrations can produce volcanic smog (Kilauea, Hawaii), causing health problems
- can be converted to sulfate aerosols which reflect sunlight and also have a role in ozone depletion
-
42
Dangers of Hydrogen Halides?
- can cause acid rain
- can poison water supplies, agricultural crops and grazing land
43
Volcano prediction
- aviation hazard mapping shows where it is dangerous to fly over
– satellite imagery shows deformation of glaciers
– seismometers measure earthquakes which often occur before an eruption – 20 magnitude 2 earthquakes leading up to E15 2010
- Soufriere hills volcano – lava dome inflation led to the forecasting of a repetitive cycle of eruptions (Anomaly) – often hard to predict
44
Volcano monitoring
- space and ground-based observations for improved monitoring and evaluation of volcanic hazards and open data policy – Iceland
- German Research Centre for Geosciences using drones to observe the lava dome
- Rain gauges in lahar regions
- Acoustic flow meters detecting ground vibration
- Tilt meters
- Satellite observations
- Measurement of gas, water and rock chemistries
- Gas emissions
- Ground deformation
- Thermal monitoring
45
Volcano preparedness
- education
- refuge and evacuation points
- warning systems
- white island - low perception of risk due to it being a tourist destination
- Iceland - failure in warning system for Hekla eruption
- Hawaiian population - low understanding of volcano risk
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