Tectonic Processes And Hazards Flashcards
What is a tectonic hazard?
Natural events formed due to tectonic activity (subduction) which has the potential to threaten both life and property
What are the three main tectonic hazards
Earthquakes
Volcanoes
Tsunamis
Give two examples of past volcanic eruptions
Mt. Vesuvius, Italy 79ad
Nevado del Ruiz, Columbia- 1985
Eyjaffajokull- 2011
Mt Toabora- 1815
Give to examples of past earthquakes
Sendai, Japan- March 2012
Sumatra, Indonesia - December 2004
Why is the pacific rim know as the ring of fire?
75% of earths volcanoes are located here
90% of earths earthquakes occur here
What are the four types of plate boundary
Destructive
Constructive
Collision
Transform
What happens at constructive plate boundary
Two oceanic plates move apart or crease new land
Mid-Atlantic ridge
Effusive eruptions and earthquakes
What happens at destructive plate margins
A continental and oceanic plate come together the oceanic plate subducts underneath the continental crust
—> —. ____
What happens at transform margins
Two plates slide past each other
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The San Andreas fault line
Powerful earthquakes
Why does the uk appear to be free from major tectonic hazards
It isn’t near any plate boundaries
What is an intro-plate earthquake
Earthquakes that occur in the middle of tectonic plates where the pressure of the tectonic plate being squashed and forced to move builds up and is released through cracks in the rocks associated with fault zones resulting in an earthquake
Where is an example of intra-plate earthquakes
Mississippi valley
What is the reelfoot rift zone
Which is a basin of an old lake which now how loose sediment at its base
Why are ancient fault lines found running through the middle of tectonic plates?
750 million yrs ago NA split from supercontinent RODINA leaving faults in central NA
What is a scar zone
Zones where fault lines were found in the past
What can cause earthquakes along scar zones?
- Movement of molten rock below the earths surface causes an intense build up of pressure which is later released along the faults
- Activity along existing margins may if strong enough cause reactivation of weakened areas
What is intra-plate volcanism
Volcanic activity away from a plate boundary
What is another name from infra-plate volcanism
Hotspot
What is a hotspot
Is an area on earths surface that exists over a mantle plume
What is a mantle plume
An area under the rocky outer layer of earth (crust)
Where magma is hotter then surrounding magma
Heat from extra hot magma melts and thins the earth
Ate mantle plumes affected by plate movement
No- magma plumes remain stationary
This creates a chain of progressively older hotspot volcanoes with only one remaining active.
What is an example of a intra-plate island chain
South-Pacific island chain
What is the formation of a hotspot
Thin weakness on crust allows magma escape onto the surface
Ocean water cools the magma over time the land grows to become a submarine volcano
When the volcano breaches the surface it becomes a volcanic island
Move from hotspot becomes a island
Erosion becomes seamount
What is the structure of the earth top to centre
Crust/lithosphere
Asthenosphere
Mantle
outer core
Inner core
What does rheid mean
Semi molten
How thick/warm is the crust
100km
Up to 400*c
Made up of oceanic and continental
What are the properties of oceanic crust
Basaltic rock
Denser then continental 3G/cm*3
Around 6km thick on average
What are the properties of continental crust
Made of granitic rock
Density = 2.7g/cm*3
On average around 40km thick
What are the properties of the asthenosphere
Semi-molten
80 to 200km
Less the 1300c
3.3G/cm3
What are the properties of the mantle
Liquid material
2900km thick
3.4g/cm3
3700c
Iron, nickel and magnesium
Properties of the outer core
2200km thick
Liquid iron and nickel
4500-5500c
12.6 and 13g/cm3
What are the properties of the inner core
2440km thick
5200c
Solid
9.9 and 12.2g/cm3
Iron and nickel
What are convection currents
Created by the mantle radiating heat outwards from the inner core caused less dense material to rise
Silicate rush metal is under immense pressure and when heated behaves like a viscous liquid
What do convection currents do
Carry heat from the core to the upper mantle
Plates will move according to the convection currents
What is seafloor spreading
When the plates split apart
Occurs at mid ocean ridges where new oceanic crust is formed
What is ridge push
When magma pushes the plates apart
Continuous linked to sea floor spreading
Not accepted don’t think it’s powerful enough as there are no tensional force in the mantle
What is slab pull
More accepted theory
Gravitational pull of subducted lithosphere is what causes plate movement
The plate sinks at an ocean trench pulling the rest of the plate
What are fissure eruptions
Key feature of volcanic activity in zones of active rifting on land
Basaltic lava
East African Rift Valley
What is the fossil evidence for continental drift
1910 Alfred Wegner
Mesosaurus (freshwater) separated by Pacific Ocean
Africa and SA have different climates in present day
What are sediment cores used for
Taken from ocean floor to date the crust
What is paleomagnetism
Study of earths past magnetic field in rocks by looking at the formation of iron in the rocks
How many times does earths polarity reverse every 1 million years
4 times
How does rock respond to changes in earths polarity
Iron in the molten magma line sup parallel to the magnetic field at the time of eruption
Why are the magnetic bands symmetrical (iron bands)
As each side of the mid ocean ridge is moving apart at the same speed
What the equation for annual rate of spreading
Distance moved in cm
——————————-
Number of years taken
Where do intraplate earthquakes occur in the US?
New Madrid seismic zone central USA
How many significant earthquakes were recorded in the new Madrid seismic zone between 1811 and 1812?
3 ranging from 7.3 to 7.5
