Hazards Flashcards
what is a natural hazard
an event that poses a threat to human life, the built environment and the natural environment
what are the 3 main types of hazards
geophysical - caused by earth processes
hydrological - caused by the occurance, movement and distribution of surface and ground water
atmospheric - caused by processes operating in the atmosphere
how does the UN define a disaster
• 10+ people are killed
• 100+ people are affected
• a state of emergency is declared
• International assistance is called for
why do people stay in hazard risk zones?
-hazard events are unpredictable
-lack of alternatives
-changing level of risk
-cost/benefit
-perception
how is risk measured?
r = h x v
c
r = risk
v = vulnerability
c = capacity to cope
what is hazard perception
the way in which a person understands or interprets a hazard. People tend to respond to hazards based on their perception
what is the fatalism approach to hazards
an optimistic or accepting approach, where people may believe that hazards are a fact of life or ‘acts of god’
what is the domination approach to hazards
hazards are predictable and can be better understood by scientific research
what is the adaptation approach to hazards
hazards are influenced by natural and human events and so we can change our lives to reduce the impacts
what is a primary hazard?
a hazard directly related to the event
eg, lava flows are directly related to a volcanic eruption
what is a secondary hazard?
a hazard that occurs due to a primary hazard
eg, a lahar is indirectly related to a volcanic eruption
what is a short term response?
occur in the days and weeks immediately after a disaster
mainly search and rescue and helping the injured
what is a long term response?
responses that go on for months and years after a disaster
involves rebuilding and taking steps to boost the local economy
what is vuberability?
the diminished capacity of an individual or group to anticipate, cope with, resist and recover from the impacts of a hazard
can relate to exposure to hazards, political instability, poverty, etc
what factors influence perception?
-education
-wealth
-religion, culture or ethnic background
-vunerability
-age
-previous experience of hazards
-family and marital status
-occupation/ employment status
-values, personality and expectations
what is a disaster?
a major hazard event that causes widespread destruction to a community or region, with significant social, economic and environmental losses
the affected community is unable to cope without outside help
what is resilience?
the sustained ability of a community to utilise available resources to respond too, withstand and reviver from the effects of natural hazards
what does integrated risk management do?
-identify the hazard
-analyse the risk
-establish priorities
-treat the risk
-implement a risk reduction plan
-develop public awareness and community strategy
-monitor and review the whole process
what are the ‘4 Ps’ of hazard management?
Prediction
Preparation
Protection
Prevention (not always possible)
why is the hazard management cycle useful?
-simplify complex events
-useful when responding to hazards with severe time constraints
-comparing actual conditions with a model leads to better understanding, so better response
-help people understand the hazards
-allow better integration of relief and recovery
what are the limitations of the hazard management cycle?
-responses are often more complex, and not always logical
-timescale is not accounted for, the model suggests equal time for each phase
-does not consider environmental conditions that might affect severity of the hazard
-all hazards are different and the model does not account for this
-evaluation and analysis of hazards are important in order to prepare for future hazards
-some countries do not have the means to mitigate effectively
-does not consider international aid
why is the park model useful?
-tool to analyse the different types of response and the sequence in which they happen
-useful for pinpointing the different kinds of response needed at different stages of a disaster
what are the limitations of the park model?
-does not take varying capacity to cope into account, and different places will take longer to reach different points of relief, rehabilitation and reconstruction
-far too general and not specific enough about impacts, frequencies, and how these affect the capacity to respond
-a model is an ideal to compare and critique, never a perfect fit
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describe the motion of constructive plate bounderies
plates move away from eachother in opposite direction, causing magma from the mantle to rise to the surface, forming new crust
what are the geological features associated with constructive plate bounderies?
-mid ocean ridges
-rift valleys
-gentle, effusive volcanoes with low viscosity basaltic lava
-volcanic islands
how are mid-ocean ridges formed?
-constructive plate boundery
-magma rises from the mantle forming new crust
-forms chains of submarine mountain ridges
-regular breaks called transform faults cut across ridges
-these faults may widen at different rates, causing frictional stresses to build up
-this tension is released by shallow focus earthquakes
how are rift valleys formed?
-constructive plate bounderies
-formed when the lithosphere stretches
-causing it to fracture into sets of parallel faults
-the land between these faults then collapses into deep, wide valleys separated by upright blocks of land called hosts
how are volcanic islands formed? (constructive plate bounderies)
-volcanic eruptions along mid-ocean ridges can build submarine volcanoes
-over time these may rise above sea level to create volcanic islands
-eg, Ascension Island
describe the motion at destructive plate bounderies
one plate moves toward another, or two plates move towards eachother
what happens at a destructive plate boundery between an oceanic plate and a continental plate?
the heavier oceanic plate is subducted
this causes the continental plate to ‘scrunch’ and form fold mountains
the exact point of collision is marked by bending of the oceanic plate to form a deep sea trench
the descending oceanic plate starts to melt beyond 100km deep and melts completely by 700km deep thud zone of melting is known as the Benioff Zone
the melting crust creates magma less dense than the surrounding asthenosphere, which rises in plumes, passing through faults in the buckled continental plate to form explosive volcanic eruptions of viscous andersitic lava
friction causes tension that builds up and is released as intermediate or deep focus earthquakes
what happens at a destructive plate boundery between two oceanic plates?
-the denser or slower moving plate is subducted under the other
-forms a deep sea trench
-rising lava from the benioff zone forms crescents of submarine volcanos which may form volcanic island arcs (eg. Mariana Trench and Marianas Islands)
what happens at a destructive plate boundery between two continental plates?
-no subduction as they are both less dense than the asthenosphere
-colliding plates uplift, compress and buckle to form fold mountains (eg, Hymalayas)
-no subduction, so no volcanoes
-shallow focus earthquakes
-young fold mountains are continously compressing and growing taller
describe the motion at conservative plate bounderies
two plates slide past eachother, causing friction
what are the geological features associated with conservative plate bounderies?
-tension forms fault lines
what are the hazards associated with constructive plate bounderies?
-gentle, effusive volcanic eruptions of low viscosity basaltic lava
-shallow focus earthquakes along transform faults at mid ocean ridges and parallel faults at rift valleys
what are the hazards associated with destructive plate bounderies?
-explosive volcanic eruptions of viscus andersitic lava from the melting Benioff Zone at oceanic-oceanic and oceanic-continental bounderies
-intermediate or deep focus earthquakes at oceanic-oceanic bounderis
-shallow focus earthquakes at continental-continental bounderies
what are the hazards associated with conservative plate bounderies?
-no subduction, so no volcanoes or formation of new crust
-powerful earthquakes
-friction between the two moving plates leads to stresses building up whenever any ‘sticking’ occurs. These stresses are released as powerful shallow focus earthquakes (San Andreas Fault System)
what is the crust?
the outermost 5-70km of the lithosphere
the layer of solid rock on the earth’s surface
what is the lithosphere?
the crust and uppermost solid mantle
the outermost 100km of the earth’s surface
what is the asthenosphere?
the layer of mantle 100-250km from the Earth’s surface
the uppermost semi-molten mantle
describe Icelandic eruptions
-basaltic lava that flows in long, parallel fissures
-effusions (constant steady stream rather than eruption)
describe hawaiian eruptions
-fluid lava that flows from the volcanoes summit and radial fissures
-forms shield volcanoes
-effusive to gentle eruption
describe strombolian eruptions
-clots of thick, incandescent (glowing due to heat) lava
-moderate bursts of expanding gasses that eject clots of lava in cyclical or nearly continuous eruptions
-gentle to explosive
describe vulcanian eruptions
-small explosions of viscus lava
-moderate explosions of gas laden with volcanic ash that forms dark, turbulent eruption clouds
-explosive to severe
describe peleean eruptions
-explosive outbursts that generate pyroclastic flows
-severe to cataclysmic
describe plinian eruptions
-gas rich magma
-gasses boiling out of of gas rich magma cause enormous and almost continuous jetting blasts that core out the magma conduit and rip it apart
-ash clouds can reach the stratosphere and generate their own lightning
-cataclysmic to paroxysmal
how are basic shield volcanoes formed?
eruptions of very runny lava from a ventral vent forming gentle, sloping cones
where are basic shield volcanoes found?
-mid-ocean ridges
-rift valleys
-hot spots
how are acid dome volcanoes formed?
eruptions of viscus lava that doesn’t flow very far, creating steep sided convex volcano cones
what is tephra?
rock fragments ejected during a volcanic eruption
what are the warning signs of a volcanic eruption?
-seismic activity
-ground deformation
-upward movement of iron-rich magma
-rising groundwater temperature and/or gas content
-small eruptions
-emissions of gasses
-landslides
-rockfalls
how is seismic activity measured and what does it indicate? (volcanicity)
seisometers, recorded using a seisomograph
microquakes indicate rising magma fracturing and cracking the overlaying rocks
how is ground deformation measuread and what does it indicate? (volcanicity)
tiltometers and laser-based elecrtonic distance measurement
bulging of the ground is caused by rising magma
how is upward movement of iron-rich magma measured and what does it indicate? (volcanicity)
magnetometers
changing magnetism within the volcano is a common geophysical indication of rising magma
how is rising groundwater temperature and/or gas content measured and what does it indicate? (volcanicity)
hydrological instrumentation
rising magma will both heat groundwater and corrupt it with gas such as sulphur (which increases its acidity)
how are warning signs such as small eruptions, emissions of gasses, landslides and rockfalls measured and what do they indicate? (volcanicity)
remote sensing equipment
remote solar powered digital camera surveillance is a powerful and safe tool for monitoring changes in and around the main crater
thermal imaging and gas sampling of emissions such as chlorine can also be included in remote sensing
what are the primary hazards of volcanoes?
-lava flows
-pyroclastic flows
-tephra
-volcanic gasses
what are the secondary hazards of volcanoes?
-ground deformation
-lahars
-landslides
-possibly tsunamis
describe lava flows as a volcanic hazard
-primary
-basaltic fissure eruptions are fastest at up to 50km/h on steep slopes, so the most dangerous. can spread more than 8km from their source
-can bury roads, cars and housing developments (Hawaii)
-1,000°c, causing fires when it comes close to buildings
-normally people have time to get out of the way
describe pyroclastic flows as a volcanic hazard
-primary
-a mixture of hot tephra fragments, lava particles and ash mixed with hot gases
-associated with andersitic or rhyolitic volcanoes and the collapse of lava domes
-move at up to 300km/h and can reach 40km from their source
-temperatures withing the flow are commonly between 100-700°c
describe volcanic dust, ash and tephra as a volcanic hazard
-primary
-ash build up on roofs can collapse buildings
-ash infiltrates machinery and quickly wears out moving parts
-fire ash from an eruption is hazardous to aircraft - when heated inside a jet engine it creates a liquid that sprays around the turbine and sets as a glassy coating which blocks airflow and shuts down the engine
describe volcanic gas as a volcanic hazard
-contaminates land and drinking water
-causes crops to fail
-affects people and livestock
describe lahars as a volcanic hazard
-secondary
-volcanic ash mixes with water to form a dense slurry similar to freshly mixed concrete
-the lahar can flow downslope at at over 50km/h
what are seismic waves?
the vibrations from earthquakes that travel through the earth
what is the focus of an earthquake?
the initial point of rupture, where an earthquake begins
what is the epicentre of an earthquake?
the point on the earth’s surface directly above the focus
how do P (primary) waves travel
-longitudinal
-vibrations in the same direction as the direction of travel
-arrive at the sensor first
how do S (secondary) waves travel?
-transverse
-vibrations are at right angles to the direction of travel
-arrive at the detector second
what to L (long) waves do?
shake the ground from side to side
how are earthquakes measured?
the moment magnitude scale
what is the moment magnitude scale?
a way of measuring earthquakes
based on the total moment release of the earthquake
log scale (base 10)
what is the mercalli scale?
a way of measuring earthquakes
measures how much damage is caused based on observations
scale of I to XII
changes according to distance from the epicentre
what is the richter scale?
a way of measuring earthquakes
the energy is released is proportional to the magnitude
log scale
how do we predict and prepare for earthquakes?
-earthquake warning systems
-individuals and businesses have response plans to prevent chaos
-tsunami warning systems
-authorities ensure evacuation routes are well signposted
-communities establish search and rescue teams
what are the warning signs of an earthquake?
-microquakes
-bulging of the ground
-decreasing radon gas concentrations in groundwater
-raised groundwater levels
-increased argon gas concentrations in soil
-curious animal behaviour
-electrical and magnetic changes within local rocks
what are the primary hazards of tropical storms?
-strong winds
-storm surges
-coastal and river flooding
-landslides
what is the threshold ocean temperature for tropical storms to form?
26°c
what is a wildfire?
the generic name for an uncontrolled rural fire
what is a crown fire?
a fire that spreads across tree canopies and affects forested areas
fastest
what is a surface fire?
a fire that burns across surface vegetation
what is a ground fire?
a fire that burns underneath the ground in layers of dry organic peat
slowest
what is the ladder effect?
the process of fires from the forest floor spreading to the canopy
what conditions does fire need?
-fuel
-ignition
-oxygen
what are the causes of wildfires?
natural:
-el nino
-lightning
-drought
human:
-arson
-cigarettes
-campfires
-controlled burning
-fireworks
