Tectonics EQ1 Flashcards
define a natural hazard
a naturally occurring event with the potential to cause loss of life or property
define a natural disaster
where a natural hazard causes social, environmental and economic damage which a population can’t cope with using it’s own resources
define vulnerability
peoples ability to cope with a hazard event
describe the earth’s core
inner most area
inner core = solid center, mostly iron, hottest part (6000)
outter core - semi-molten, mostly liquid iron & nickle, temps around 4500-6000
describe the earth’s mantle
widest layer
upper mantle = soild
outer mantel = semi molten
- forms the asthensophere
describe the earth’s crust
oceanic crust = thin ( 6-10 km) , dense, forms ocean floors
continental crust = thicker ( 45-50 km ), less dense, forms landmass
What is the asthenosphere?
the upper layer of the earth’s mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.
What is the lithosphere ?
the crust & upper mantle
what are the 4 ways tectonic plates move ?
- slab pull
- subduction
- mantle convection
- seafloor spreading
Describe subduction
as two plates move towards each other, one slides into the mantle and into the subduction zone
if it’s an oceanic & continental plate, oceanic will subduct as it’s denser
describe slab pull
newly formed oceanic material at mid ocean ridges becomes denser & thicker as it cools
this causes it to sink into the mantle, pulling the plate down
describe mantle convection
heat produced by radioactive decay in the core heats the lower mantle
creates convection currents in the earths asthenospher, causing plate movement
Describe sea floor spreading
when the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added.
As a result, the ocean floors move like conveyor belts, carrying the continents along with them
What are convection currents?
he heat from the core is transferred to the mantle. Liquid rock, close to the core, is heated and rises.
When it reaches the crust it is forced sideways as often it can not pass through the crust.
The friction between the convection current and the crust causes the tectonic plate to move.
The liquid rock then sinks back towards the core as it cools.
the process then repeats.
What is paelomagnetism
a record of changes in earth’s magnetic fields
when lava solidifies, minerals line up with earth’s magnetic direction
mid - ocean ridges show patterns of magnetic direction mirrored on each side of the ridges
describe divergent boundaries
constructive margins
two plates diverge forming new crust in the form of mid ocean ridges in sea, and rift valleys on land
what are mid - ocean ridges ?
extend underwater as mountain chains with transform faults cutting across them
mild - shallow focus earthquakes can occur
volcanic eruptions cause submarine volcanoes, occasionally growing above land e.g Iceland
what are rift valleys ?
form on continents where crust form parallel cracks ( faults )
and the land between them collapses, creating steep valleys
describe convergent boundaries
destructive margins
plates converge & denser oceanic crust slides beneath lighter crust. there are 3 types.
what happens when an oceanic plate meets continental plate ?
( convergent boundaries )
oceanic crust slides into upper mantle and melts, creating deep ocean trenches
subduction leads to fold mountains, where plate collision causes folding
constant moving = friction
friction causes major earthquakes in the benioff zone.
what happens when two oceanic plates meet ?
subduction of the lighter of the two plates
deep ocean trenches & volcanoes formed
submarine volcano grow to form volcano island arcs
shallow to deep focus earthquakes occur
what happens when two continental plates meet ?
collision margin occurs
rock forced up to form high fold mountains
e.g Himalayas
shallow focus earthquakes
Where do most earthquakes occur?
95% occur along plate boundaries
How do earthquakes occur?
friction between plates builds up and creates pressure
pressure is released when rocks fracture along faults
energy released = seismic waves
pressure is released from the hypo centre
seismic waves radiate from the hypo centre
describe the 3 types of seismic waves ?
primary (P) = fastest, reach surface first, travel through solids & liquids, shake backwards & forwards, least damaging
secondary (S) = slower, travel through solids, move sideways, shake at right angels to direction of travel, more damaging than P waves
surface love (L) = slowest, last to arrive, most damaging, shake ground side to side, larger, focus all energy on earths surface
What are secondary hazards of an earthquake ?
liquefaction = surface rock becomes more liquid than solid during movement, buildings & roads sink, power lines explode ( see Christchurch )
landslides = caused by ground shaking, cause a large portion of earthquake damage & death ( see Pakistan 2005 )
what are the primary hazards of an earthquake ?
crustal fracturing & ground shaking
describe the formation of a volcano
as plates move, pressure builds and hot magma & gas rise from within the upper mantle to the crust
once the magma reaches land it’s the lava
as the lava cools, it forms rock, so volcanoes grow
describe lava flows ( primary hazard, volcanoes )
occur on the surface and can reach 1700 degrees Celsius
not a real threat to people as they move slowly
some fast flowing basaltic lava destroys anything in it’s path
What is basaltic lava?
Low silica content (45-55%)
Fluid as low viscosity (low gas content)
Effusive (non explosive) & regular eruptions
Flow quickly over long distances
What is rhyolitic lava?
Highest viscosity & highest content of silica (68%)
Flows slower than andesitic & basaltic lava
Ooze from erupting stratovolcanoes after violent pyroclastic flows
describe composite volcanoes
acidic lava = viscous
steep so lava won’t flow far
layers of ash & lava
violent
long periods between eruptions
describe shield volcanoes
basaltic lava, non acidic, very runny
gentle slides = lava flows before solidifying
just lava, no layers
frequent eruptions
describe pryroclastic flows ( primary hazard V )
fast moving
mix of hot (700 degree ) rock, ash & gas exploded from volcano
dangerous
describe ash & tephra falls ( primary V )
volcanic rock fragments & ash blasted into the air during eruptions
can damage, injure or kill anything
ash can travel thousands of kilometres & block sun & breathing
describe gas eruptions ( primary V )
dissolved gasses released during an eruption
includes water vapour, CO2 & sulphur dioxide
can travel far & are dangerous
describe Lahars ( secondary V )
flows of rock, mud and water down volcanic slopes
can be hundreds of meters wide and flowing tens of meters per second
form when ice & snow melt, or heavy rainfall happens during an eruption
erodes loose rock & soil
Describe Jokulhlaups
formed when heat from an eruption melts snow and ice
sudden releases of water, rock, gravel & ice
very dangerous
what are intra - plate earthquakes ?
happen within a tectonic plate
cause uncertain, likely due to ancient fault lines becoming active again
distribution is random = hard prediction
describe hot spots
form in the middle of a plate when rising plumes of magma then erupt on the ocean floor = a volcano
as the plate moves over a hot spot, the volcano is carried away with it, and a new volcano replaces it
this creates a chain of volcanic islands ( see Hawaii )
describe the formation of a tsunami
can be generated by landslides or even the eruptions of volcanic islands, but most are generated by sub-marine earthquakes at subduction zones.
- generated when a sub-marine earthquake displaces the sea bed vertically as a result of movement along a fault line at a subduction zone.
- violent motion displaces a large volume of water in the ocean water column, which then moves outwards from the point of displacement.
- The water moves as a vast ‘bulge’ in open water, rather than as a distinct wave.
- As the waves approach shore they slow dramatically, wavelength drops but wave height increases.
- Tsunami usually hit coastlines as a series of waves (a ‘wave-train’) in an effect which is more akin to a flood than a breaking wave.
- Sub-marine earthquakes that occur close to shorelines can generate intense ground shaking damage, followed by damage from the subsequent tsunami. ( see Indian ocean tsunami 2004 )
what are the impacts of a tsunami ?
sweep for miles inland and cause buildings, trees & foundations of buildings to be removed & destroyed
change the landscape & smaller islands may be completely destroyed
flooding = contamination
describe the use of DART systems
is an early warning system
DART stations use sensors and buoys to monitor changes in sea level
if tsunami waves are detected, info is sent via satellites to warning centres
the warning centres use computer modelling to estimate the size & direction of the tsunami and info areas at risk
outline 2 places the DART system has been used
INDIAN OCEAN
- had an early warning system since 2006
- when the 2004 tsunami hit Sri Lanka before the warning system was in place, 31,000 ppl died
( see boxing day tsunami )
JAPAN
- has the worlds most extensive tsunami warning system
- in 2011, Japan’s meteorological agency issued a tsunami warning within 3 mins of the earthquake
- however the size was underestimated so few steps were taken to prepare
