plate tectonics, volcanoes and earthquakes Flashcards
types of plate boundaries (3)
- divergent plate boundaries
- transform boundaries
- convergent plate boundaries
shield volcanoes form
in constructive plate boundaries in oceans
what type slopes do shield volcanoes have ( gentleor not, what degrees)
gentle, less than 10º
what shape do shield volcanoes have when looked at from above
circular or oval
why do shield volcanoes have gentle slopes
because the magma has a low viscosity meaning it can flow quicker and get further from the vent and solidifies at a bigger distance from the vent.
is the eruption of a shield volcano explosive and why
The eruption isn’t very explosive because the viscosity of the lava is much lower than composite cone volcanoes and so can just ooze out as its more runny
do shield volcanoes have a thin or thick vent
thick
when is a constructive/divergent plate boundary formed
when 2 plates move apart (diverge)
and magma rises up from the gap created and cools
example of a constructive plate boundary
mid atlantic ridge
destructive plate boundaries form when
2 plates push against each other
how are fold mountains formed
when at a destructive plate boundary, one of the plates is pushed down while the other is pushed up and squashed, and that sediment forms fold mountains
are earthquakes and volcanoes common on destructive plate boundaries
yes
why are volcanoes common at destructive plate boundaries
- 2 plates move against each other
- one is subducted
- as the plate is moved down the rock melts due to the pressure and heat
- pressure is built up
- magma rises to the earths surface
when do transform plate boundaries form
when they slide sideways against each other
are volcanoes or earthquakes common at transform plate boundaries
volcanoes are rare
earthquakes are common
why are earthquakes common at transform plate boundaries
friction between the 2 plates causes eartquake
example of a transform plate boundary
san andreas fault
where do you find volcanoes, fold mountains and earthquakes
NEAR plate margins
what is the ring of fire
an area around the pacific ocea where there is the greatest concentration of active volcanoes
earhquakes happen at what type of plate margins
transform
destructive
divergent
process of an earthquake
- as 2 plates move towards each other, one can be pushed down into the mantle
- if this plate gets stuck, then it causes strain in the surrounding rocks
- when this tension in the rocks finally gets released, it produces shock waves ( seismic waves)
what are seismic waves
shock waves
what is the point where the earthquake starts called
the focus
what is the epicentre
point on earths surface right above the focus
where are the waves of an earthquake the strongest
near the epicentre
once seismic waves start, what do they do
start to spread out from the focus
what scale measures earthquakes
Reichster
how is the magnitude of an earthquake measured
using a seismometer
serious earthquales have a reichster scale of around
5-9
if a volcano is extinct
it will never erupt again
if a volcano is dormant
it hasn’t erupted in a long time
if a volcano is active
it has erupted recently and will likely erupt again
composite volcanoes eject what substances (4)
Lava (thick and slow-moving).
Pyroclastic materials (ash, tephra, pumice, volcanic bombs).
Volcanic gases (water vapor, CO₂, SO₂).
Pyroclastic flows (hot, fast-moving clouds of gas and debris).
why is a composite volcano cone shaped
because when the molten lava has erupted it cools and hardens quickly, so does not reach very far
very viscous lava
do composite cone volcanoes have steep or gentle sides
steep ( 30º top and 8º at the bottom
what is a caldera
Huge craters caused by when volcanic cones collapse into empty magma chambers after a powerful explosion/eruption (the whole volcano blasts out)
shield and composite volcanoes are made of
lava
composite volcano is made of
lava and ash
a dome volcano what lava
acidic and thick ( quite viscous) which causes steep sides and hardens quickly
why do people live in earthquake and volcanic zones (4)
- volcanic lava and ash make fertile soils so people settle and have a farm nearby
- precious minerals and fossil fuels are found near voclanoes
- land is cheap and people feel safer because they have housing that is protected from it
- volcanic activity can heat underground water forming hot water springs, electricity, heating houses
how do scientists monitor if a volcano will erupt (clues they look for) (4)
- lots of mini earthquakes
- rising magma detected under the earths surface
- escaping gas
- changes in tilt of volcano sides
how do scientists predict earthquakes (clues they look for) (4)
- changes in well water levels
- gas emissions
- cracks appearing in rocks
- sometimes strange animal behaviour
ways of planning to reduce the effects of a hazard (7)
- monitoring helps predict so that people can be warned
- families can organize supplies and water rations before hand just in case so they’re ready
- local emergency services be trained and ready
- disaster plans can be drawn by local authorities and governments
- people can be trained on emergency procedures
- roads and buildings can be built in order to undertake them
- strengthening roads and buildings
earthquakes and volcanoes cause more problems for what type of countries
LEDC
Factors that affect how serious the disaster is
- rural/ urban areas ( rural areas have less people and buildings so size of disaster is smaller)
- population density ( the more people, the more deaths)
- how prepared countries are ( if countries have planned ahead and are developed, they have the money to potect their people, but if you don’t have moeny to build houses that can go through an earthquake then the diaster will be bigger)
what do MEDC do when there is a disaster
emergency plans
what do emergency plans consist of
- local authorities asses the seriousness of the situation and damage
- citizens are kept informed
- immediate emergencies are delt with first
- power, electricity and water are restpred as soon as possible
- communication networks are fixed as soon as possible
- NGO’s actions are coordinated
- life gets back to normal once risk is clear
how are LEDCs not prepared (3)
- people haven’t been given information on what to do in case of a disaster
- some don’t have prepare plans due to not enough money or resources
- many people live in towns which don’t have proper access to roads and bad housing which means help can’t get there and more chance of injury
why does getting back to normal take longer for LEDCs (8)
- fewer experts do access situation
- more damage due to badly built housing
- without prepare plans, things will take longer
- help takes longer to arrive due to bad communication facilities
- limited communications means people won’t be alerted
- shortage of money
- power and water will take longer to be fixed as it was bad in the begginning
- medical facilities are limited so more untreated injuries and deaths
types of crust
oceanic and continental
characteristics of oceanic crust
thinner 5km
denser
characteristics of continental crust
thicker 20-50km
less dense
order of the earths crust (5)
lithosphere
asthenosphere
mantle
outer core
inner core
what is a volcano
dent in the earths crust through where magma flows
how do volcanoes form at divergent plate boundaries
- as the two plates move apart there is a gap formed between them
- magma rises to fill that space and a volcano is formed
what are HOT SPOTS
stores of magma that are pushed up, so rise up through weaknesses in the earths crust to form volcanoes
what type of plate is the pacific ring of fire on
divergent ( pacific plate being submerged)
ash clouds form in
violent eruptions (composite volcanoes)
ash clouds travel ___ distances by the ___ and can cause effects on ___
long
wind
other countries
lava can flow up to
10km
ash can cause
burying and destruction of plants and crops
as well as suffocation/asphyxation of animals and humans
volcanoes release __ gases like __
toxic
carbon monoxide
what are lava bombs
due to large build up of pressure, lava boulders can be emitted + cause severe injury to people + buildings
what is pyroclastic flow
fast moving current of hot lava and gas moving at fast speeds away from the volcano
