Tectonic Processes And Hazards Flashcards
(55 cards)
What are theories of the structure of the earth based on
Seismic activity at the earths surface, study of magma
Describe the internal structure of the earth
Inner core- ball, iron and nickel
Outer core- semi molten layer
Lower mantle- silicate rock, plasticity so can reshape under stress
Upper mantle (asthenosphere) - flowy - weaker rocks so break under stress as it is cooler- focus of eq found here
Crust-
contintental- thicker- granite, oceanic- thinner- basalt
What is continental drift
Continents drifting apart and back together
What did scientists think was the main cause of plate movement and how does it work
Convection currents
Mantle is hottest close to the core- so lower parts heat up, less dense so slowly rise
Move up athenosphere and become cooler, so become dense and sink.
Convection currents create a drag on the base, causing them to move
What is now thought to be the main reason of plate movement and how does it work
Slab pull
When a plate subducts, the plate sinking into the mantle, pulls the rest if the plate with it, causing further subduction
What is paleomagnetism
As tectonic plates diverge, magma rises to fill up the gap and it cools to form new crust
Under the sea, the sea floor gets wider, seafooor spreading - mid ocean ridges
On land- rift valleys
Magma is iron rich, become polarized and align with earths poles
When polarity changes, rocks will change direction, can see when it was formed and how quickly plates are moving apart
Destructive (converging) plate margin, oceanic - continental
Denser oceanic crust subduction by less dense continental crust, forms deep sea trench
Fold mountains also form where the plates meet, made up of sediments accumulated on continental crust
Oceanic crust is melted as it subducts
Pressure builds up and magma is forced through weak areas causing volcanoes (composite)
e.g- peru chile trench in Pacific
Destructive (converging) plate boundary, Oceanic - oceanic
Slightly more dense one will subduct, deep sea trench
Earthquakes in subduction zone, leads to tsunamis
Possible for for volcanoes as well, lava cools and creates island arcs
e.g- Mariana islands and Mariana Trench
Collision plate margin
Neither crust is subduct
Crust fold up against each other, mountains
e.g - Himalayas
Constructive plate boundary (diverging)
Mantle is under pressure from plates above, when they move, pressure is released
Release caused mantle to melt, producing magma
Magma rises through gap to produce new crust or erupts to form volcano
Since plates do not move apart in a uniform way, pressure builds up, cause earthquake
Ocean ridges, rift valleys
Conservative plate margin
movement is horizontal, moving in opposite directions, or same direction, different speeds. increased friction, may lock together which causes pressure to build up. earthquake caused when they jolt apart
e.g - san Andreas fault
where do earthquakes occur and how are they caused
caused by the build up and sudden release of tension at all 4 types of plate margins
majority occur in ring of fire, edge of plates
also occur in middle of plates. intraplate earthquakes.
due to old fault lines moving into heir resting positions or new fault lines developing.
how does the strength of earthquakes vary
type of plate margin- highest is destructive
depth of focus- shallow focus is higher magnitude
describe characteristics of primary waves
fast moving, act in one direction. phases of contraction and expansion
travel through solids liquid and gas
don’t produce much damage
describe characteristics of secondary waves
slower moving, vertical vibrations
only travel through solids
more damage than primary waves
describe characteristics of love waves
horizontally but at right angles to P waves
surface waves that follow from S waves
only through solids
cause most damage such as fracturing the ground.
what is soil liquefaction
occurs in areas of loose, waterlogged ground
earthquake vibrations place groundwater under pressure
pressure forces water through soil, causing ground to act like liquid
soil becomes weak and easily deformed,
e.g- Christchurch New Zealand
how do landslides occur
shaking of ground dislodges rocks and soil
move down slope due to gravity
shaking of ground loosens ground, water infiltrates and extra weight may tigger earthquake
e.g- nepal
how do tsunamis form
submarine earthquakes,
seafloor moves up and down
water column displacement
what are areas of volcanic activity that are not near plate margins called. how do they work
mantle plumes
vertical column of magma rise up from mantle - hotspot
chain of volcanoes forms as crust moves but mantle plume remains stationary.
how is the explosiveness of a volcano determined
how easily gasses can escape from lava- if gas is trapped, pressure builds
explosive reaction
viscosity of lava- contains lots of silica or are cooler are more explosive
what lava is formed at constructive plate margins
balsatic lava
1000-1200
low silica
low viscosity
eruptions are frequent and longer duration
less violent
shield volcanoes n
what lava is formed at destructive plate boundaries
andesitic and rhyolitic
650* - 1000*
high silica
more viscous- may form blockages in vent so more explosive
composite volcanoes
primary hazards of volcanic eruptions
lava flow- speed and distance based on viscosity
pyrococlastic flow- gas, ash, rock
volcanic gases- water vapour, co2, Sulphur dioxide, poisonous, colourless
tephra- all pieces of rock, damage buildings, atmospheric haze
