Tectonics Flashcards
Pangea
All of the continents were previously connected as one super continent
How are fossils evidence of the theory of plate tectonics?
Fossils of the freshwater mesosaurus are found in both south Africa and south America
How is coal evidence of the theory of plate tectonics?
Coal can be found in antarctica, it couldn’t have formed there at its current latitude, it needs tropical conditions.
How are maps evidence of the theory of plate tectonics?
Maps of the ocean floor show the 11km marianas trench in the phillipines.
Who created the continental drift theory and what is it?
1) Alfred Wegner
2)Continents move around the earth like rafts
Where are earthquakes and volcanic activity?
Plate boundaries
Why do tectonic plates move?
Convection currents from earth’s core
Convection currents definition
Hot liquid magma currents that move in circles in the asthenosphere causing plates to move
Seafloor spreading definition
Mid ocean ridges/underwater mountains form when hot magma is forced up from the asthenosphere. New crust created splits plates
Subduction definition
As new crust is created in one place its destroyed in another. As 2 oceanic plates move to eachother one slides under the other into the mantle.
Convergent plate boundaries + example
The denser oceanic plate subducts under the other plate. The oceanic plate melts in the Benioff zone. Magma forces itself up to the surface. Eg Mt St Helens Washington state USA.
Divergent plate boundaries + example
Rift volcanoes. Less explosive. Non viscous lava. Basaltic lava. Eg mid Atlantic ridge.
Describe Mt Kilauea Hawaii.
-Hawaii islands created by pacific plate moving NW over hot mantle plane.
-High heat + low pressure at the base of lithosphere melts the rock
-Magma rises through fissures forming volcanos.
-Plate moves over hotspot. Existing active volcanos moved from hotspot
-New volcanos formed
-Old volcanos cool and subside
Effusive volcanos
High temp, low viscosity, high dissolved gas content, divergent margins, low silica, narrow base
Explosive volcanos
Low temp, high viscosity, low dissolved gas content, subduction zone, high silica, wide base
Paleomagnetism
Result of the zone of magma striking the Earth’s magnetic polarity when it cools. Used to determine historic periods of tectonic activity by remaking plate boundaries.
Hypocentre
The point within the Earth where an Earthquake rupture starts
Liquefaction
Where water saturated material temporarily loses normal strength and behaves like a liquid due to the pressure of strong shaking. Occurs in saturated soils.
Primary waves
-Type of body waves
-Compression wave/longitudinal
-Moves through solid/liquid/gas
Secondary waves
-Type of body waves
-Transverse/ move up and down/side to side
-Sheering waves
Love wave
-Type of surface wave
-Moves side to side
-High amplitude
Rayleigh wave
-Type of surface wave
-Move in an elliptical motion
-Further reach
-
Surface waves
slower
large
more destructive
Why are Earthquakes dangerous?
Soil liquefaction
buildings collapsing
landslides
tsunamis
How do buildings collapse
S and L waves shake the ground violently and can cause buildings to collapse especially if weak foundations
How do tsunamis happen?
-An Earthquake, volcanic eruption or landslide happens underwater
-Water is displaced. Rises due to tectonic energy
-Gravity pulls the water down as a wave
(One side of crack goes up forcing water above that piece with in)
Water is dragged to back to sea first (drawback)
Human factors( Tsunamis)
-Power infrastructure
-Population
-Education/preparation
-Warning system
-Coastal development
-urban/rural
Physical factors(Tsunamis)
-Magnitude of earthquake/size of landslide
-Distance from epicentre
-Coastal inlet- higher wave
-Relief (flat land is worse, easier for wave)
-Timing
-Gradient of shore
-Ecosystem
-Amplitude, water column displacement,
Example of a tsunami:
Asian tsunami 2004 was caused by destructive plate boundary east of thai coastline
Hazard definition
A perceived natural event that has the potential to threaten both life an property
Disaster definition
The realisation of a hazard that causes significant impact on a vulnerable population. Over 100 affected
What makes a population vulnerable (Deggs disaster model)
Poor infrastructure
Clean water
Healthcare
Education
Warning systems
Politics
Population density
Root causes (pressure and release model)
Limited access to power, structures, resources
Political/economic systems
Dynamic pressures (Pressure and release model)
Lack of training/investment/press freedom
Rapid population change
Rapid urbanisation
Deforestation
Moment magnitude scale
Measure of the energy released by an earthquake based on the “seismic moment” of an earthquake on a logarithmic scale
Richter scale
A measurement of the height of waves produced by earthquakes on a logarithmic scale
Mercalli scale
A measurement of the impacts of an earthquake based on people’s experiences
Volcanic explosivity index
A measurement of the volume of material ejected from a volcano, height of cloud and other observations. Logarithmic scale
Limitations of hazard event profiles
Don’t show human factors like capacity to cope