Hazards Flashcards
Avalanche
A slide of a large snow or rock mass down a mountainside caused when a build up of snow is released.
Landslides
Similar to Avalanches except instead of snow, it involves pieces of the earth, such as dirt, trees and rocks. Landslides can be caused by earth quakes, volcanic eruptions and unstable land.
Mudflows
A special case of landslides in wish heavy rainfall causes loose soil on steep terrain to collapse and slide downwards.
Flood
The result of prolonged rainfall that isn’t able to drain from an area fast enough
Wild fire
An uncontrolled fire burning in wildland areas. Can be caused by drought or human negligence.
Cyclonic storms
Also called hurricane and typhoon. A storm system that forms over oceans. Caused when evaporating water comes off the ocean and becomes a storm.
Tornado
A natural disaster resulting from a thunderstorm. Violent, rotating columns of air which blow at speeds between 50 and 300 mph.
Lahar
A large amount of material, including mud, rock and ash sliding down the side of a volcano at a rapid pace during an eruption. Associated with heavy rains.
Earthquake
The ground shaking or moving sideways. Usually occur along plate boundaries due to two or more plates moving, causing energy to be released.
Tsunami
A wave of water caused by the displacement of a body of water. Can be caused by underwater earthquakes, or landslides.
Volcanic eruption
The point in which a volcano is active and releases its power. Usually occurs along plate boundaries due to plates moving apart, releasing lava from the mantle.
Hazard risk
The probability that a natural hazard may take place.
Hazard risk
The probability that a natural hazard may take place.
Hazard perception
The way we react in different ways to hazards, because of the differences in the way we process and filter infomation.
Potential factors in hazard response
Wealth, Age, Gender, Religion, ecenomic development of nation, hazard magnitude, hazard frequency.
Fatalism
When people accept the risk and consequences of living in a hazardous area, due the potential reward. Eg fertile soil near volcanoes
Adaption
When an area changes their way of living in order to be able to live with hazards.
Prediction
Predicting when a hazard takes place in order to reduce the impact. Includes: seismic monitering, measuring gas volcanic gas emissions, satellite observations, geological ground changes and odd animal behaviour before an earthquake.
Mitigation
Any action taken to reduce or eliminate the threat to property or human life.
Risk sharing
Spreading the risk of a natural hazard resulting in any one group’s / individual’s risk reducing. Can involve spreading financial burden
Management
An umbrella term for any actions taken to reduce the impact of natural hazards. Adaption, prediction, mitigation, and risk sharing.
The Park model
A model of hazard response considers how the standard of living and economic status of an affected area changes following an event.
Relief phase
The immediate response, focusing on saving lives and property. Urgent medical supplies may be brought in.
Rehabilitation phase
May last several months - efforts are made to restore physical and community structures, at least temporarily.
Reconstruction, mitigation, preparing.
Permanent changes are introduced to restore the quality of life and economic stability to at least the pre-disaster level (or more). Can also include mitigation and preparing for future hazards.
Slab pull
At subduction zones gravity ‘pulls’ the oceanic plate down into the mantle. This destroys crust material and keeps the earth in shape.
Ridge push
The process of material pushing out from the ridge is known as ridge push
Lithosphere
The solid top layer of crust in which plates are formed. Consists of crust and upper mantle.
Asthenosphere
Soft, plastic like rock in the uppermantle just below the lithosphere
Destructive margin
One plate sinks under another (subduction)
Constructive margin
Two plates move away from each other
Conservative
Two plates move past each other
Collision margin
Two continental plates move together
Continental crust
25-70km thick
Aprox 4 billion years old
Density 2.7 gcm^-3
Consists of oxygen, silicon, aluminium, iron, calcium
Granite, sedimentary and metamorphic rocks
Oceanic crust
6-7km think
Aprox 200 million years old
Density 3gcm^-3
Consists of silica and magnesium primaraly
Basalt and gabbro rocks
Pieces of evidence for plate tectonics
- Jigsaw fit
- Tectonic evidence
- Geological fit
- Paleomagnetism
- Fossil evidence
Paleomagnetism
New material is constantly being produced at the mid ocean ridge and takes the polarity of the earth of when it was made. Earth’s magnetism randomly flips sometimes meaning we can see a striped pattern in the polarity of the rock. This could only be possible due to the sea floor moving due to plates.
Jigsaw fit
The similarity in the outline of the coastlines of eastern South America and west Africa points to the continents being moved by the movement of plates. Gaps or overlaps can be explained by coastal erosion and deposition.
Tectonic fit
Fragments of an old fold mountain belt around 425 million years old are found widely spread across multiple continents today
Geological fit
When the geology of eastern South America and West Africa was mapped it revealed that ancient rock outcrops over 2000 million years old were continuous from one continent to the other
Fossil evidence
There are many examples of fossils found on separate continents and nowhere else, suggesting the continents were once conjoined
Ocean Ridges
A line of undersea volcanoes created by tectonic activity.
Rift Valleys
A lowland region that forms where Earth’s tectonic plates move part
Graben
Areas that have dropped in a rift valley.
Horst
Areas that rise in a rift valley.
When continental and oceanic crust meet at a destructive boundary
Subduction occurs; the thinner and denser oceanic crust sinks below the continental crust into the mantle.
Very seismically active - violent volcanoes and earthquakes
Deep ocean trenches and fold mountains formed
When two oceanic crusts meet at a destructive boundary
Subduction occurs; one plate is forced under the other, due to it being marginally denser or moving quicker.
Causes earthquakes, some of which can be very powerful.
Ocean trenches and island arcs are formed, for example Marianas trench.
When two continental plates meet at a destructive boundary.
Continental plates are of lower density than the asthenosphere beneath them therefore subduction does not occur.
The plates instead collide, causing very powerful earthquakes e.g Nepal 2015.
Sediments from vanishing ocean floors are compressed to form fold mountains.
The two types of volcanoes
Shield Volcanoes
Composite volcanoes
Shield Volcanoes
- Gentle slopes and wide base
- Frequent eruptions of high speed, non-viscous lava that flows for long distances
- Usually non violent eruptions
- Found at constructive boundaries
Composite volcanoes
- High and steep sided with a narrow base
- Explosive eruptions of viscous lava and ash that does not flow far from the crater
- Layers of alternating ash and lava
Icelandic volcano
Low viscosity and highly effusive.
Hawaiian
Effusive, minor explosivity, with fire fountain and low viscosity lava flow
Strombolian
Eruption with gas bubbles so eject tephra
Vulcanian
Higher gas build up than Strombolian, highly viscous lava. A series of short lived explosions, with tephra including bombs
Pelean
Explosive eruptions with range of tephra with nuee ardent pyroclastic flows
Plinian
Highly explosive, large eruption column, range of tephra and pyroclastic fallout, including flows
List of volcanic hazards
Lahars
Mudflows
Terphra
Nuees ardentes
Lava flows
Gases
Acid rain
Ash fallout
Pyroclastic flow
Methods of monitoring volcanoes
Geological observations
Seismic activity
Gas emissions
Geological observations
Looking at physical aspects of a volcano to predict eruptions.
Often, the volcano expands before an eruption due to magma filling it. This can be recorded by measuring the volcano’s tilt, distance, or horizontal movements with GPS.
Seismic activity
Seismic activity always occur as volcanos are preparing to erupt. This can be measured with a seismograph or by monitoring infra sound. Spikes in seismic activity can indicate an eruption is going to happen.
Gas emissions
Spikes or drops in gas emissions, such as sulphur dioxide can indicate an oncoming eruption.
Examples of lava control ideas
Bombing lava tubes
Cooling the lava flow with water
Building a barrier
Adding concrete blocks to the flow to divert its path.
Seismicity
The earth shaking
Steps to seismic waves
1) Pressure builds at the point where two plates meet
2) Sudden release (due to rock failure)
3) The waves cause the ground to shake
4) The intensity of the shaking is determined by the depth of the focus and the energy release
5) The result is the earthquake hazard
Types of seismic waves
P Waves
S waves
Rayleigh waves
Love waves
P waves
Fastest waves
Move the ground forwards and backwards
Least damaging
S waves
Slightly slower than P waves
Go up and down
Far more damaging than S waves
Rayleigh waves
Much slower even than S waves
Compression up and down more slowly
Can be more damaging
Love waves
Side to side movement
Most destructive
Slow
Tsunamis
Caused by seismic waves under the sea
A large volume of water that pushes inland
Plates move which displace water, causing it to flow to land
Liquefaction
The mixing of sand or soil and ground during the shaking of a moderate or strong earthquake. When the water and soil are mixed, the ground becomes very soft and acts similar to quick sand.
Methods of predicting earthquakes
-Past seismic events
-Remote sensing (plate movements, surface temperature etc..)
-Radon gas emissions
Primary effects of earthquakes
- Liquefaction of saturated soils
- Buildings + infrastructure damage
- Immediate deaths from crushing, falling glass, fire etc..
- Slope failures setting off landslides
Secondary effects of earthquakes
- Power cuts restrict emergency services
- Flooding from blocked rivers
- Fires caused by broken gas pipes
- Panic, fear, hunger
Long term effects of earthquakes
- Bodies not cremated / buried - disease spread
- Long term ‘lost generation’
- Problems restoring trust in neighbours and civil services
- Education suspended
- Long term trauma / grief can lead to reduced life expectancy
Measuring earthquakes
Seismometers are used to measure seismic activity. These plot a seismograph which can be used to determine how much shaking occured
There are two scales used; the modified mercalli scale and the richter scale
The Richter scale
- Measures the ground deformation and energy release during a seismic event
- Logorithmic. For example, 3 is 10x greater than 2
- The greater the magnitude the less frequent the hazard
- News agencies and scientists use it as its more scientific as it used actual data rather than subjective observations
The modified Mercalli scale (MMI)
- A subjective view of the effects of a seismic event
- Has a scale that goes from I to XII, the later being the most destructive
Tropical storm definition
A violent rotating storm which occurs at the mid- latitudes (5 - 30 degrees N/S of the equator)
Formation of Tropical storms
1) Strong upward movement of air draws vapour up from the warm ocean surface
2) The evaporated air cools as it rises and condenses to form thunder storms
3) Condensing air releases energy which powers the storm further
4) Several small thunderstorms combine to form a join spinning storm, and a tropical storm is officially born
5) Storm develops an eye where air rapidly descends
6) Storm carried across the warm ocean, continuing to gather energy
7) When it hits the land, the storm loses energy due to friction aswell as no more warm water being available
Monitoring tropical storms
1) Aircraft and drones fly around and inside tropical storms, collecting data on wind speeds, pressure, rainfall and snow.
2) Satellites can take large top down view of satellites in order for scientists to gauge the scale of a storm. They can also make 3D scans and measure temperatures within the storm
3) Computer models are able to use large amounts of data to quickly process large amounts of data to create accurate predictions on the development of storms.
Magnitude of Tropical storms
The magnitude of tropical storms are classed using the saffir-Simpson scale. It puts storms into 5 categories based on sustained wind speeds.
Convection
The process of hot magma rising in the mantle which reaches the crust and caused plates to move
Hazards associated with tropical storms
- Strong winds
- Storm surges (caused by low pressure increasing tide height)
- Heavy rainfall
- River flooding
- Landslides
Wildfire definition
Any kind of rural fire which is uncontrolled and spreading
Ladder fuels
Fuels that allow fire to travel vertically upwards
When high, fire can spread more easily due to sparks and embers spreading further
Causes of wild fires
Human activity and involvement are the main causes of wild fires.
For example, in the last 90 in the USA 61% of wildfires were caused by arson.
Favourable conditions for wildfires
- Plants with low water content are more easily burnt
- Dry, hot conditions
- Wind can carry ash and embers, spreading the fire.
