Volcanoes / earthquakes Flashcards
what are the 3 different types of plate boundaries?
- convergent
- divergent
- conservative
explain and describe convergent (destructive) plate boundaries?
continental and continental
oceanic and oceanic
continental and oceanic
convergent plate boundaries are plates which are moving towards each other.
- when two continental plate move towards each other they will form a fold mountain range, because they are made of relatively low density rock. eg. Himalayas
- when two oceanic plates converge with each other they will create volcano islands , because the eruption occurred under water. (pacific subducting under Philippine
- when a continental and an oceanic plate converge, subduction occurs. this will lead to earthquakes and fold mountains. (Nazca and South American plate).
explain and describe divergent (constructive) plate boundaries:
these are found when two oceanic plates move AWAY from each other. when the two plates move away from each other the gap between them will be replaced by magma, if a lot of magma escapes, submarine volcanoes will form, which might lead to volcanic island in the future.
(eg. iceland)
information about conservatory plate boundaries:
this is when two plates slide past each other. no magma rises, no subduction occur. however this isn’t smooth. it builds up stress in the rocks, eventually this pressure will release and create an earthquake.
what is subduction?
subduction occurs when a denser and heavier oceanic plate is dragged down under a lighter continental plate forming a deep ocean trench.
what is a hotspot?
a hotspots are locations where there is strong volcanic activity going on under the earths crust (eg. in hawaii)
what is a collision margin?
this is when 2 plates with the same srength and density move directly into each other an are squeezed upwards.
(eg. Himalayas)
is the distribution of earthquakes and volcanoes similar?
yes. in the way that they both occur along plate boundaries.
what is the pyroclastic flow?
pyroclastic flow is a devastating eruption of extremely hot gas, ash and rocks. it travels very fast (up to 200km/h)
what are the volcanic hazards?
- lava flows (destroy farmland, lives and houses)
- ash ( destroys crops, loss of income)
- roofs can collapse
- gas emissions (kill)
- pyroclastic flow
what are the earthquake hazards?
- buildings collapse on people (death)
- can cause fires
poorly designed buildings are a major hazard
definition of an earthquake?
a sudden and brief period of intense shaking of the ground.
what is liquefaction?
when an earthquake occurs and the floor a building is standing on is so weakened that the building sinks into the ground because the now softer, weaker rocks cant hold the weight of the building.
what affects the amount of damage an earthquake causes?
- the depth of the focus ( the shallower the more damage)
- the type of rock
what can an earthquake under the sea cause
a tsunami. (high waves)
how are volcanic eruptions measured?
they are measured using a logarithmic scale (from 1 to 8)
it measures the volume and the height if the ash ejected into the sky.
it is measured using the volcanic explosivity index (VEI)
how are earthquakes measured?
you can use 3 different scales:
- Richter scale (amount of energy release, using a seismograph (0 to 10)
- Mercalli scale (what people actually feel)
- Moment magnitude scale (the measures energy released by the earthquake)
how much stronger is an earthquake measuring an 7 in the RICHTER scale than one measuring a 6?
10 times stronger.
on what factors does the damage and destruction caused by a natural disaster depend on?
- scale
- energy
- size of the affected area
- density of the population
- where people well prepared or not?
- are people pre-warned?
- how well can a country cope after the disaster (immediately and long term)
know the disaster risk equation:
risk = ——magnitude/frequency x vulnerability———-
capacity to cope
what the primary impacts of earthquakes?
- collapsed buildings
- broken water, gas, sewage pipes
- downed electric power lines
what the secondary impacts of earthquakes?
- tsunamis
- aftershocks
- fires
- economical issues
what is an aftershock?
a short weaker earthquake which happens after the big one and make building which are already weakened collapse.
what the primary impacts of volcanoes?
- buildings, roads and crops destroyed
- death and injuries
- contamination of water supplies
what the secondary impacts of volcanoes?
- lahars created
- fires
- traumas
- economical issues
what is a lahar?
is a very sticky, dense mixture which you get stuck in. it is created by mixing water/ rainfall water with mud and volcanic ash.
why do people still live in these dangerous areas?
- unaware
- unable to move away (family)
- minerals
- fertile soils
- tourism
- work
prediction for earthquakes: how, what..
- to know where and when the hazard will happen
risk assessments for earthquakes?
- means the probability of this event happening
- use:
- distribution
- frequency
- scale
- predictability
- location
- use drones and google maps (technology)
preparation for earthquakes:
- educate people
- find shelters
- evacuate people
once an earthquake occurs buildings which are poorly built collapse very easily, these have to be rebuilt much safer.
what are ways of building these safer
- levitating homes - a cushion inflates a few mm to absorb the energy, but it is expensive.
- stronger materials (different) (flexible)
- high technology (different structure to build)
warning systems for earthquakes:
it is impossible to precisely predict when an earthquake will occur.
despite best preparation, earthquakes will always still create damage. you can just decrease the amount of damage.
