Hazards Flashcards
What is a Hazard
A hazard is an event which has the potential to cause harm to the environment, people or the economy
When does a hazard become a disaster
when harm actually occurs to the environment, people or the economy
What are the categories of natural hazards and some examples in each
Tectonic and geological hazards include:
earthquakes, volcanic eruptions, landslides and tsunami
Climate and meteorological hazards include:
storms, floods, droughts and tornadoes
Biological hazards include:
pests and diseases
Risk
the probability of an event happening and the scale of its possible damage.
What factors affect the risk
The ability of a population to take preventative or precautionary measures, known as adjustment or mitigation, and their ability to cope.
How easy the hazard events are to predict.
The frequency of events.
That some places may experience more than one type of hazard (hazard hot spot e.g. Philippines or California).
The severity of the hazard.
Structure of the earth
Crust
0-70km thick
Continental and Oceanic Plates
Solid -> Granite and Basalt
10 C
Mantle
2900 km thick
Solid, but flows - RHEOLOGICAL CONSISTENCY
375 C
Outer Core
2200 km thick
Liquid
3000 C
Inner Core
1270 km thick
Solid due to pressure - iron and nickel
3000 C
Oceanic and Continental Crust Characteristics
Oceanic
Newer than Continental
Denser
Thinner -> 5km
Can Subduct
Continental
Older
Less dense
Thicker -> 30km
Can’t subduct
Lithosphere and asthenosphere
Lithosphere-> top 100km of the earth, crust and top part of mantle that makes up earths 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?
Ridge push
• Slab pull
• Convection currents
Worldwide distribution of earthquakes and volcanoes:
Uneven distribution.
• Mostly correlate with plate boundaries.
• Earthquakes occur in linear chains (e.g. along west coast of S America) along all types of plate boundary.
• Some earthquakes away from plate boundaries (could be due to large plate movement or due to human activity such as building dams and reservoirs or fracking which puts a lot of pressure on the earth’s crust).
• Volcanoes also in a linear distribution. Around ¾ in a ring around the Pacific, termed the ‘Pacific Ring of Fire’, and are related to destructive plate boundaries.
• Some volcanoes aren’t on plate boundaries, these are hotspot volcanoes where isolated plumes of magma rise and move up through the crust to create a chain of volcanoes e.g. Hawaii.
Types of plate boundary:
• Divergent aka Constructive
o 2 oceanic plates move apart.
o Creates effusive volcanoes and small earthquakes.
o E.g. Mid Atlantic Ridge
• Convergent aka Destructive
o Oceanic plate subducts underneath a continental plate.
o Creates powerful earthquakes and explosive volcanoes.
o E.g. Nazca plate subducting under South American plate
• Collision
o 2 continental plates collide
o Causes powerful earthquakes and fold mountains.
o E.g. Indian plate colliding with Eurasian plate
• Transform aka Conservative
o 2 continental plates slide past each other.
o Creates powerful earthquakes.
o E.g. Pacific plate and North American plate.
Volcano Formation at constructive boundary
Constructive boundary volcano formation:
Two plates move apart from each other (at a mid-ocean ridge, though can also happen at a rift valley with two continental plates moving apart). Magma rises to the surface at this weak spot and is extruded in eruptions, forming volcanoes when it solidifies to lava (remember, magma in the mantle, lava on land).
Leads to shield volcanoes (short, gently sloping volcanoes composed of basaltic lava due to its low viscosity i.e. very runny) which have effusive eruptions
Volcano Formation at Destructive Boundary
Oceanic plate subducts underneath continental plate. Oceanic plate melts due to dehydration melting. Newly created magma causes pressure buildup under the surface and eventually rises to the surface and is erupted, forming a volcano over time as more material is erupted, cools, and solidifies to lava.
Leads to strato volcanoes (tall, steep sided, volcanoes composed of alternating layers of lava and pyroclastic flow/ ash deposits due to sticky, high viscosity rhyolitic lava) which have explosive eruptions.
Hotspot Formation
A random pool of magma beneath the surface of the crust erupts through the crust due to pressure build up
As plate boundary moves old Hotspot volcano becomes dormant as the magma moves away from it so it no longer has a supply
Magma then supplies a new volcano and another one forms near the old one
What are the primary and secondary hazards of a volcanic eruption
Primary hazards: immediate effects, resulting from the eruption e.g. lava flow, ash, pyroclastic flow etc.
Secondary hazards: things that happen as a result of primary hazards e.g. water contamination, infrastructure damage.
Measured using VEI
Mt Fuego LIC Key Facts
3rd June 2018, Mt Fuego, Guatemala.
• 3763m high stratovolcano in the Pacific ring of fire.
• Cocos and Caribbean destructive plate boundary.
• Country has high levels of poverty and political instability.
• 48km from Guatemala City.
• Explosive eruption (biggest for 500 years).
• Ash cloud 10km high.
• Pyroclastic flow of over 100km/hour.
• Settlements such as El Rodeo devastated.
• Airport closed.
• 110 killed, 200 missing.
• 12,000 evacuated, 3000 housed in temporary shelters.
• 1.7 million effected.
• 8500Ha of crop damage.
• Traffic chaos from people trying to flee in their cars.
Kilauea (HIC) key facts
May 2018.
• Effusive eruption from shield volcano over a hotspot in the middle of the Pacific plate. New lava flows from the Pu’u O’o crater.
• Lava fountains.
• No lives lost.
• Property damage especially in Leilani estates and Vacationland, where nearly 700 homes were destroyed.
• House insurance increased six fold.
• Closure of part of the Hawaii volcanoes national park.
• Largest freshwater lake, Green lake, was vapourised.
• Coastline extended more than 1km.
• People with respiratory problems potentially impacted due to high SO2 concentrations.
• 10,000 residents evacuated, and a few airlifted by helicopter.
• Governor declared a state of emergency.
Earthquake definition and formation
A sudden and brief period of intense ground shaking.
Caused by:
1. Plates get stuck due to friction, often caused by protrusions on the opposite plate.
2. Pressure builds up.
3. Pressure gets too great and plates slip. The slipping motion causes energy to be released in the form of seismic waves, which is an earthquake.
What are the different types of earthquake wave, which one causes damage?
P waves:
Primary waves. Pull ground side to side.
S waves:
Secondary waves. Pull ground up and down.
Primary do the damage
What are 4 precursor events to an earthquake
Precursor events:
• Small tremors in preceding months
• Increase in radon emissions
• Indicators of previous earthquakes e.g. fault lines (fault scarps) and seismic gaps
Strange animal activity e.g. mass migrations
What impacts amount of deaths from earthquakes
• Age of building/ if they have been made ‘life safe’ or ‘earthquake proof’ via stringent building codes; remember ‘earthquakes do not kill people, buildings do’.
• Infrastructure damage.
• Potential for ground liquefaction.
• Population density
• Poverty
• Poor governance
• Depth of focus (shallow focus (<10km) quakes will have a greater impact).
• Strength of earthquake.
• Number of aftershocks
• Level of development.
• Time of day
• Distance from epicentre
• Proximity to secondary hazards e.g. tsunamis, landslides etc.
What are the scales for earthquakes
Measured on the Mercalli Scale (effects i.e. intensity) or Richter Scale (strength i.e. magnitude).
Nepal earthquake case study key facts
• 25th April 2015
• Midday, Gorkha district.
• Magnitude 7.8 on richter scale
• Impact made worse by poverty.
• Collision margin of Indian and Eurasian plates.
• Focus 15km deep.
• Kathmandu region was raised by 1m, Mt Everest sank 3cm.
• 300 aftershocks (Magnitude 4 to 6.7)
• Secondary hazards: landslides, flooding, avalanches on Everest.
• 9000 killed, 23,000 injured.
• 8 million affected.
• 90% tourist bookings cancelled during immediate aftermath, losing $600 million during 2015-2017.
• 1.4 million people required food assistance.
• Aid from WHO, Red Cross etc.
Italy HIC case study earthquake key facts
• Amatrice, in the Apennines, August 24th 2016
• Magnitude 6.2
• Eurasian and African plate meeting at destructive margin.
• Occurred within a seismic gap left between earthquakes in 1997 and 2009.
• 298 dead (inc tourists as it was the summer season)
• 03.37 local time, so many were asleep and crushed by houses.
• 4000 made homeless.
• Lots of buildings collapsed as many affected places were ancient hilltop settlements, which hampered the response too.
• Antiseismic construction laws introduced in 1973, but concrete beams are often used instead of wood (which can be subjected to more stress) and the Mafia often obtain building permits and don’t follow legislation, which worsens impacts.
• 50 million euros worth of emergency funding was authorised by the government.
