1.3 Flashcards
What are P Waves?
P (primary) waves caused by compression pushing and pulling in the direction of travel (pulsing
These are the fastest and first to arrive
What are S Waves?
S (secondary) waves are slower
These waves only move through solid rock in an up and down movement.
What are L Waves?
L (Love) waves only travel through the surface of the crust. Fastest surface wave. Moves from side to side as it moves forward. Causes most damage due to longer wavelength and focus of energy at the surface.
What are seismic waves
primary, secondary, love from the hypo centre in a circular motion from the focus
What is the hypo centre/focus?
The point at which friction and energy is released from in the ground
What is a fault?
a fissure/line that is between plates/boundary
What is an epicentre?
the point on the surface directly above the focus
What factors the severity of an earthquake?
magnitude = how much energy
distance from focus/epicentre = impact over time
bedrock/soil = saturated area (liquefaction?)
What is the difference between primary and secondary hazards?
primary = shaking and crustal fracturing (initial)
secondary = ‘side-effects’ of primary hazards
-> tsunamis, landslides
Why is it difficult for buildings to stay intact during an earthquake?
- more than one type of waves
- can cause secondary problems (liquefaction, landslides)
- waves can destroy buildings quickly eg L waves
What is liquefaction?
liquefaction = loosely packed sand becomes saturated as water takes up pore spaces.
Causes loss of bonds making solids act like water
Causes buildings structure to fail
What are landslides?
When slope processes cause mass movements and therefore, areas to collapse due to the pressure and energy.
Can be natural
Earthquakes over 4 are more likely to cause these mass movements
What are the types of volcanoes?
Composite and shield volcanoes
What are some characteristics of a composite volcano?
cone volcanoes have form from viscous lava that is rhyolitic and andesitic so is quite runny and flows without building layers
These are ususally at sub-duction zones
These are steep sided
And more likely to have pyroclastic flows
What are some characteristics of a shield volcano?
form from lava with low viscoity basaltic so it cant run and forms layers.
This usually happens as hotspots and mid ocean ridges
These are less steep and very wide
What are the 3 types of lava?
basaltic
andesitic
rhyolitic
What is basaltic lava?
hottest (1000-1200c) mostly CO2, Fe,Mg low gas content materials melting from upper mantle thin and runny low viscosity gently effusive hot spots, ridges, shield volcanoes
What is andesitic lava?
800-1000C intermediate silica 3-4% gas content subducted oceanic plates + seawater slow movement violent somewhat explosive composite volcanoes and subduction zones
What is rhyolitic lava?
650-800C cataclysmic supervolcanoes or composite cone volcanoes highest silica content 70% 4-6% gas melting of lithospheric mantle and slabs thick and stiff viscous
What is the runniest and thickest lava?
runniest = basaltic thickest = rhyolitic
What are primary hazards of a volcano?
Lahars, acid rain, ash flow, fumeroles, fire, pyroclastic flows, landslides - debris avalanche,
What are secondary hazards of a volcano?
volcanic bombs, ash cloud (tephra fall), lava, pyroclastic flows, jokulhlaups
Where do volcanoes occur?
convergent margins with oceanic + continental
divergent either
hot spots
What are lahars, fumeroles, jokulhaups, pyrolastic flows, tephra?
Lahars = mudflow because of heat and destabilisation
fumeroles = gas from volcano released
jokulhaups = type of glacial outburst flood because of heat and eruption
pyroclastic flows = fast moving lava or gas
tephra = rock ejected from a volcano
What is a tsunami?
an abnormal wave that is greater than average due to previous tectonic activity and can cause major damage as a secondary hazard
What are features of a tsunami and how are they formed?
they have long wavelength (150-1000km) low height towards the coast (0.5-5m) come as a series (train) fast velocity up to 600kph formed = volcanic eruptions and landslides, destructive boundary where continental flips upwards 90% on pacific basin
Where are the high risk zones?
along coastal countries like america, eastern asia, japan,
How are tsunami waves formed by earthquakes?
when there is subduction and build of elastic and continental builds up tectonic strain causing release of energy. This releases energy in a water column displacement as mega thrust to upwell.
This is released as a series of waves
What is a water column displacement?
its is a direct vertical upwards of water straight to the surface the energy therefore carries on throughout in a circle eg indian ocean 2004
What are the main features of an volcano?
Magma chamber
Conduit/pipe
Vent
Dome
How does liquefaction effect buildings after and before?
Before : loosely packed grains are held by friction and filled with water in pore spaces
After : shaking destabilises the soil by increasing space between grains. With this structure lost it flows like a liquid
Describe one secondary hazard associated with earthquakes?
tsnuamis - wavelength, water displacement column
Liquefaction - removes solidity of particles move like a liquid
Landslides - from disturbed particles
What are 4 primary hazards of volcanic hazards?
Ash
Pyroclastic Flows
Volcanic bombs
Volcanic gases
Are volcanic eruptions a unique natural hazard?
YES = more predictable (eg water turns brown, gas samples, longer duration (active volcanoes many years eg Hawaii) therefore, evacuation takes longer, only hazard with visible magma and can see what is beneath the surface.
What are 4 secondary hazards from a volcanic eruption?
acid rain, jokulhaups, landslides, lava flows, ash flows, fumeroles, lahars
