Hazardous Environments Flashcards
Define hazards
An extreme that threatens people, their property and settlements
Define disaster
When a hazard causes widespread destruction to property and human lives
How hazardous or disastrous an event is also dependant on…
Risk - the probability of an event happening and scale of its possible damage;
The ability of a population to make adjustments or mitigation and their ability to cope;
How easy the hazards events are to predict;
The frequency of the event;
Some places may be in experience more that one hazard (eg Philippines);
The severity of the hazard.
Types of hazards
-geological (eg volcanic eruptions, earthquakes)
-climatic (eg tropical storms)
Outer core
- 2200km thick
- liquid
- 3000 C
Crust
- 0-70km thick
- continental and oceanic crust
- solid —> mainly granite and basalt
- 10 C
Mantle
- 2900km thick
- solid, but flows
- 375 C
Inner core
- 1270km thick
- solid —> mainly iron and nickel
- 3000 C
Oceanic crust
- newer (less than 200 millions years old)
- denser (heavier)
- thinner —> 5km
- can subduct (go under into mantle)
Continental crust
- older (1500 millions years old years old)
- less dense
- thick —> 30km
- can’t subduct
Lithosphere
Top 100km of the earth (ie crust and top part of the mantle) that makes up earth’s tectonic plates
Asthenosphere
The rest of the upper part of the mantle that acts as a lubricant for the tectonic plates to move on
How do tectonic plates move?
- slab pull
- ridge push
- convection currents
How does slab pull work?
Occurs when a dense oceanic plate sinks into the mantle at subduction zones. As it sinks, it pulls the rest of the plate along with it, creating movement
How does ridge push work?
At mid-ocean ridges, magma rises to form new crust. As this crust moves away from the ridge, it pushes the plates apart, causing them to move
How does convection currents work?
These are circular movements of molten rock in the earth’s mantle caused by heat from the core. Hot material rises, cools, and sinks, creating currents that drag the plates along the surface
Worldwide distribution of earthquakes and volcanoes
- uneven
- mostly correlate with plate boundaries
- earthquakes occur in linear chains along all types of plate boundary
- some earthquakes occur away from plate boundaries, this could be due to human activity like mining, fracking etc
- volcanoes also occur in a linear distribution, like around the pacific ring of fire, and are related to destructive plate boundaries
- other volcanoes are not on plate boundaries, called hotspot volcanoes, they occur where plumes of magma rises and meets the crust and form a chain of volcanoes eg Hawaii
Types of plate boundaries
- divergent aka constructive
- convergent aka destructive
- collision
- transform aka conservative
Divergent aka constructive plate boundary
- when 2 oceanic plates move apart
- creates effusive volcanoes and small earthquakes
- eg Mid Atlantic Ridge
Convergent aka destructive plate boundary
- when oceanic plate subduct underneath a continental plate
- creates powerful earthquakes and explosive volcanoes
- eg Nazca plate subduct under South American plate
Collision plate boundary
- when 2 continental plates collide
- causes powerful earthquakes and fold mountains
- eg Indian plate colliding with Eurasian plate and forming the Himalayas
Transform aka conservative plate boundary
- when 2 continental plates slide past each other
- creates powerful earthquakes
- eg Pacific plate and North American plate
Constructive plate boundary volcanoes formation
- Two plates move apart from each other (usually at mid-ocean ridge, though can also happen at a rift valley with 2 continental plates pulling apart).
- Magma rises to the surface at this weak spot and is extruded in eruptions, forming volcanoes when it solidifies to lava
- This leads to shield volcanoes
Destructive plate boundary volcano formation
- Oceanic plate subducts underneath continental plate
- Oceanic plate melts due to dehydration melting.
- Newly created magma rises to the surface and is erupted, forming a volcano over time as more material is erupted, cools, and solidifies to lava
- Creates strato volcanoes
Shield volcanoes
Shot, gently sloping volcanoes composed of basaltic lava due to its low viscosity ie very runny.
These have effusive eruptions
Strato volcanoes
Tall, steep sided, volcanoes composed of alternating layers of lava and pyroclastic flow / ash deposits due to sticky, high viscosity rhyolitic lava.
These have explosive eruptions
Hotspot formation
The plate above the magma plume moves, but the plume stays put, forming a chain of volcanoes
Volcanic features
- magma chamber
- crater
- lava flow
- secondary vent and cone
- volcanic bombs (strato)
- ash cloud (strato)
- pyroclastic flow (strato)
What is used to measure eruptions of volcanoes?
Volcanic explosivity index (VEI)
What are Primary hazards?
Immediate effects, resulting from the eruption eg lava flow, ash, pyroclastic flow etc
What are Secondary hazards?
Things that happen as a result of primary hazards eg water contamination, infrastructure damage etc
Mt Fuego volcano case study (LIC)
- 3rd June 2018, Mt Fuego, Guatemala
- strato volcano in Pacific ring of fire
- at destructive plate boundary
- country has high levels of poverty and political instability
- 48km from Guatemala City
- explosive eruption (biggest for 500 years)
- ash cloud 100m high
- pyroclastic flow over 100km/hr
- settlements devastated
- 1.7 million effected
- 8500Ha of crop damage
- scientists warned of eruption 8hrs before, but took 3 hrs for evacuation to be issued
Kilauea volcano case study (HIC)
- May 2018
- effusive eruption from shield volcano over a hotspot in the middle of the Pacific Ocean
- lava fountains
- no lives lost
- property damage — 700 homes destroyed
- house insurance increased sixfold
- coastline extended 1km
- largest freshwater lake
What is an earthquake?
A sudden and brief period of intense ground shaking
Earthquakes are caused by…
- Plates get stuck due to friction, often caused by protrusions on the opposite plate
- Pressure builds up
- Pressure gets too great and plate slips. The slipping motion causes energy to be released in the form of seismic waves, which is an earthquake
Which plate boundaries does earthquakes occur at?
All plate boundaries
What are P waves?
Primary waves, pulls ground side to side.
What’s are S waves?
Secondary waves, pulls ground up and down
What are some examples of precursor events?
- small tremors in preceding months
- increase in radon emissions
- indicators of previous earthquakes eg fault lines and seismic gaps
What are some factors that impact the death toll?
- Age of building / if they have been made ’life safe’ or ’earthquake proof’ via stringent building codes; REMEMBER: earthquakes do not kill ppl, buildings do
- Potential for ground liquefaction
- Population density
- Poverty
- Poor governance
- Depth of focus (shallow focus <10km quakes have greater impact)
- Strength of earthquake
- Number of aftershocks
- Level of development
- Time of day
- Distance from epicentre
- Proximity to secondary hazards eg tsunamis, landslides etc
How are earthquakes measured?
Either the Mercalli Scale (measures effects ie intensity) or Richter Scale (measures strength ie magnitude)
Nepal earthquake case study (LIC)
- 25th April 2025
- at midday
- magnitude 7.8
- impact made worst by poverty
- collision margin of Indian and Eurasian plates
- focus 15km deep
- 300 aftershocks
- secondary hazards: landslides, flooding, avalanches on Everest
- 9000 killed, 23000 injured
- 8 million effected
- 90% tourist bookings cancelled, losing $600 million during 2015-2017
- 1.4 million ppl required food assistance
- Aid from WHO, Red Cross etc
Italy earthquake case study (HIC)
- august 24th 2016
- magnitude 6.2
- Eurasian and African plates meeting at destructive plate margin
- 298 dead
- 03:37 local time, so many asleep and crushed by houses
- lots of buildings collapsed as places affected include ancient hilltops
- Anti-seismic construction laws not followed since 1973, worsens impacts
- taxes cancelled for the worst hit settlements
- a Casa Italian
Where do tropical storms form?
In tropical oceans, 5-30 degrees N/S of the equator
Conditions for the formation of tropical storms…
- sea surface temp >27 degrees
- converging winds, forces air to rise from sea surface
- low pressure systems
- low wind shear, allows clouds to rise vertically to high levels
- Coriolis effect, cause cloud to start rotate
What wind speed counts as a tropical storm?
> 34 mph wind speed to be called a tropical storm
