Hazards resulting from tectonic processes Flashcards
What is a Hazard?
A threat that could injure people and damage the built environment
What is resilience?
How well a population recovers from a disaster
Name the three ways in which natural hazards can be classified by CAUSE
- Tectonic
- Geo-morphological eg. mass movements
- Atmospheric eg. cyclones
Name some other classifications of natural hazards
- Magnitude, size or scale
- Frequency of occurrence
- Duration
- Spatial distribution
How many earthquakes happen every year?
100,000
What percentage of volcanoes are on plate boundaries?
81%
Describe how an earthquake is caused?
When plates move via convectional drag, ridge push and slab pull this can create seismic activity which originates from the focus in the ground. Seismic waves cause the ground to shake
what is the point on the surface of the ground, directly above the focus called?
Epicenter
What is the point in the ground that seismic waves originate from?
Focus
What are the two types of seismic waves?
Body and surface
Why does depth of earthquake matter?
The lines of energy from the focus get weaker with distance so deeper earthquakes are less violent
What do you use to measure seismic waves
Seisometer
What are the seismic waves that travel the fastest?
primary waves
which arrive at the detector second?
Secondary waves
which waves travel longitudinally and which travel transverse
Primary= Longitudinal Secondary= Transverse
What are the two types of surface waves?
Love and Raleigh waves
Where do Love waves travel?
only in the surface
Describe why Raleigh waves are the most damaging
Corkscrew shape while also moving up and down. Causes the ground to lift up and down
what are the benefits and drawbacks of the Richter scale?
Benefits:Easy to read, the most widely used scale, universal
Drawbacks: Doesn’t include the impact, needs expensive equipment i the area
what are the benefits and drawbacks of the Mercalli scale?
Benefits: Only need people to see it
Drawbacks: Completely subjective so some people may have worse experiences than others and rank it higher than it was
what are some of the possible secondary hazards resulting from earthquakes?
Landslides
Soil liquefaction
tsunamis
floods
What are some of the gaseous volcanic hazards
- Water vapor constitutes for up to 80 percent of the gases emitted which can result in a lahar or mudslide once converted
- Nuree ardente: 1000c, only 2 people survived out of 30000 when one hit the capital of Martinque in 1902
What are some of the liquid volcanic hazards?
- Lava especially runny basaltic lava which flows at 50km/h
- Aa lava is the fastest flowing and is 10 m thick while Pahaehoe is slow flowing and less than 2 meters thick
What are the Solid volcanic hazards?
- Pyroclastic material
- Volcanic bombs and blocks
- Light particles can rise into the air and damage aeroplane engines
what are some examples of secondary volcanic hazards and how they occur?
- Lahars occur when water mixes (water may come from snow melt) with loose pyroclastic material and can reach 75km/h
- Landslides in the same way as above plus loading on the land of pyroclastic flows
- Tsunamis
- Flooding: most prominent in cold climates when the snow melts because of heat flow
why do people live near volcanoes?
- New land
- Fertile soil- can get three crops per year rather than 1 on the slopes of Pinatubo in the Philippines
- Geothermal energy
- Mineral resources
- business opportunities in tourism- Iceland has seen a 400% increase in tourism
- Spas and resorts - blue lagoon, Iceland
what is a cinder cone?
A cinder cone is a steep conical hill of loose pyroclastic fragments, that has been built around a volcanic vent.
what is a lava dome?
small domes formed in the craters of stratovolcanos due to the solidification of viscous lava
What is Risk?
The combination of the probability of an event and its negative consequences
What is a disaster?
A serious disruption involving widespread human material, economic or environmental losses and impacts which exceeds the ability for the community to cope using its own resources
What is disaster risk?
The potential disaster losses, in lives, health status etc which could occur to a particular community over some specified future time period
What is vulnerability?
The characteristics and circumstances of a community that make it susceptible to the damaging effects of a hazard
how can earthquakes be predicted in the long term?
- Ancient evidence of previous earthquakes
- Seismic gaps
how can earthquakes be predicted in the short term?
Monitoring precursor events
Ground uplift, foreshocks, water levels in wells, radon gas emission, animal behavior
Why can the water table show that an earthquake is approaching
Ocillations in the water table from small foreshocks and water level may rise to the surface
What is easier to predict, Volcanos or earthquakes?
Volcanos
how can volcanos be predicted in the long term?
Geological history
Recurrence of eruptions
how can volcanos be predicted in the short term?
Earthquakes: As magma moves towards the surface it usually deforms and fractures rock to generate earthquakes
Ground Deformation: As magma moves into the volcano the ground may inflate. This can be measured using a tiltmeter
Changes in heat flow: as the magma approaches the surface the temperature of the ground or the groundwater increases. This can be measured using a infrared camera
Changes in Gas composition: Prior to an eruption the levels of sulphur dioxide and hydrogen chloride increase in the volcanic vents relative to water vapour
How can GPS be used to measure ground deformation?
measures the movement of the ground as the volcano inflates
What ways can people reduce the effect of hazards?
- Controlling building in high risk areas (Land use zoning)
- Aseismic building design
What are some of the ways a building can be made more ‘earthquake proof’
- ‘Birdcage’, interlocking steel frame
- Fire resistant building materials
- Automatic window shutters to prevent falling glass
- Foundations sunk into bedrock not clay
what are the factors which influence the amount of damage caused by the shockwaves of an earthquakes?
- Size of the earthquake (richter scale)
- Depth of the focus, the shallower the focus the greater the effects
- Number and strength of foreshocks or aftershocks may weaken building further
- Distance of settlement from the epicentre
- Nature of the bedrock
- Population and building density
- Strength and type of buildings
why is a lava flow a hazard?
they can reach up to 64 km/hr but usually they are slower so only cause damage to property
why are pyroclastic flows a hazard?
can reach speeds of up to 100 km/hr meaning that few people can usually escape
why are ash falls a hazard?
- they have twice the density of snow so can cause roofs to collapse
- they kill vegetation and livestock which eat the ash covered vegetation resulting in a loss of agricultural activity
how is poisonous gas a hazard?
- they can be erupted from the volcano
- In 1986 a CO2 emission in Cameroon killed 1700 people and 3000 cattle
give an example of a lahar
in 1985 a lahar produced by the Nevado du ruiz volcano killed 23,000 people
what are some of the benefits of Volcanos?
- New land produced
- Fertile soils
- Geothermal energy eg. Iceland
- Minerals
- Industrial products
- Tourism opportunities eg. Rotorua-Whakarawarewa, New Zealand-Spa
