[Unit 1: Enquiry Question 1] Flashcards
Tectonics
Constructive (divergent) boundary
A plate boundary where two plates move away from each other. Plates move by sea floor spreading. magma rises from mantle creating new crust which pushes the plates further apart.
DRC on boundary, mt nyiragongo
Collision plate boundary
A plate boundary where two (continental & continental) plates move toward each other, neither can subduct. so they both crumple and form mountains (e.g. Himalayas)
destructive boundary
A plate boundary where two (oceanic & continental OR oceanic & oceanic) plates move toward each other, the more dense one subducts. Moves via slab pull
cause deep ocean trench, fold mountains, earthquakes (tsunamis).
Conservative boundary
Where two tectonic plates slide past each other, but where crust is neither formed or destroyed. earthquakes form from the friction build up (e.g. San Andres Fault)
Intra-plate earthquakes
These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquakes. ancient fault lines are reactivated forming seismic waves. Some may form new plate boundaries. weakened crust cracks under pressure
Intra-plate volcanoes
formed at hotspots, this is fed by a mantle plume which is an area with really hot and low density magma. This breaks through the crust and forms a volcano
Slab Pull
the pulling of a tectonic plate as its edge subducts deep into the mantle. denser oceanic plates subduct at cold downwellings. This causes cooler mantle areas. affecting convection
Oceanic Crust
7km deep. 28-400°C. low. Basalt. Solid
Continental crust
70km thick. 28-400°C. low. Granite. Solid.
Mantle
700-2890km thick. 870°C. medium. Peridotite. Solid & liquid layers
Outer Core
2890-5150km thick. 4400-6100°C. dense. Iron (mainly) and sulphur. Liquid generating magnetic field.
Inner Core
5150km-centre. 7000°C (radioactive decay). very dense. Iron (mainly) & nickel. Solid
Structure of the Earth (Chemical & Physical layers)
Oceanic crust (basalt)
Continental crust (granite)
Mantle (Peridotite)
Lithosphere - crust + upper mantle
Asthenosphere - upper mantle
mesosphere - (lower) mantle
How do plates move (divergent boundary)?
divergent plate boundaries - the crust thins as it is pulled apart, mantle rises to fill gap. This creates new seafloor. This new seafloor pushes the plates apart on either side.
How do plates move (destructive boundary)?
the less dense plate subducts into the mantle.
the older/cooler rock pulls the plate into the mantle behind it
(slab pull)
what discovery was made for tectonics in 1915
Alfred Wegner - theory of continental drift.
-fossils oceans apart (same green plants) on all continents (once all had same climate)
-mountain ranges have similar rock types. Pangea lines them up as one big mountain range
-What causes continents to move? Scientists mocked it.
what discovery was made for tectonics in 1918
Sonar tech developed.
Map ocean floor (thought it was flat at first)
They were now aware of crust under ocean (ocean floor move)
Belief isn’t credible but gaining support
what discovery was made for tectonics in 1919
Arthur Holmes - suggests convection currents in mantle
-upwards ruptures surface
-downwards causes buoyant continents to crumple into mountains
-lateral moves surface like conveyor belt
what discovery was made for tectonics in 1946
Ocean floor mapped completely.
-mid oceanic ridge
-mountains
-volcanoes
-deep ocean trenches
what discovery was made for tectonics in 1954
J.P.Ruthé - Map of volcanic eruptions & earthquake zones
what discovery was made for tectonics in 1960
Harry Hess & Robert Dietz - sea floor spreading theory
what discovery was made for tectonics in 1963
pattern of magnetic striped rock. Provides evidence for seafloor spread theory.
what discovery was made for tectonics in 1965
J.Tunzo Wilson - plate tectonics theory
what discovery was made for tectonics in 1983
GPS available for public use to track movement of Earth’s surface.
define Earthquake
caused by a sudden movement near to surface along a fault
define the Benioff Zone
Area of seismicity corresponding with the slab being thrust downwards in a subduction zone. cause multiple earthquake at once
Two types of seismic waves
body waves and surface waves
Two types of body waves
P waves and S waves
Features of P waves
- Longitudinal
- Travel through solids and liquids
- Travel faster than S-waves
-first waves to come
-compress and expand the ground
-cause buildings to expand and contract
Features of S waves
after P waves
vibrate side to side and up and down
shake ground back and forth
shake buildings
cant move through liquids
slower than P-Waves
What are the two types of surface waves
Love waves and Rayleigh waves
features of surface waves
slower
more violent
Rayleigh:
make the ground roll like ocean waves
Love:
shake from side to side
What is primary hazard (and examples)
immediately, direct result of the earthquake
e.g crustal fracture and ground shaking
What is secondary hazard (and examples)
as a consequence of ground shaking
e.g. land slides, soil liquification and tsunamis
2011 Tohoku tsunami case study
list as many facts as you can
18500 deaths
$220 billion damages
caused by magnitude 9 earthquake (focus of 24.4km)
-pacific plate subducting under Okhotsk plate
wave height was 3-40m high hitting at 35km/hr
hit Japans low lying east
surrounded by deep waters
-allowing waves to retain energy as they travelled
estuaries funnelled the waves
4.4million left without electricity
7 reactors at fukushima meltdown
transport lines damaged
what is soil liquification
When loosely packed grains of soil held together by friction get shaken by the earthquake, the soil becomes destabilized, increasing the space between grains. Soil flows like liquid.
Causes buildings to tip/sink/collapse
What determines the impact of a tsunami
-duration
-wave amplitude
-physical geography of the coast
-coastal ecosystem buffer
-timing
-coastal development & proximity from coast
what is a volcano
extrusive structure found on Earth’s surface ranging from gentle fissure eruptions to explosive composite cones.
The shape of a volcano is related to its type of lava.
What are the 3 main types of lava?
-basaltic
-andesitic
-rhyolitic
give the eruption temp, gas content, viscosity and SiO2 content of all three types of lava
Temp, Gas, Viscosity, SiO2
basaltic: high, low, low, 50%
andesitic: mid, mid, mid, 60%
rhyolitic: low, high, high, 70%
Explosivity depends on: temp, gas, viscosity and SiO2 content.
how do each of these impact the explosiveness?
higher temp increases explosion
higher gas content increases explosion
lower viscosity increases explosion
lower SiO2 increases explosion
what are pyroclasts
in all explosive eruptions
hot fragments projected
damage on impact
what is tephra
all explosive eruptions
collective term: airborne or ground-flowing pyroclasts
major destruction over distances
what are landslides
disturbing of land by magmatic pressure
flows of rocks, mud and tephra
destruction of property and land
what are poisonous gases
any eruption
gases (HCl, CO2, HF, SO2)
Toxic (1700 in Cameroon (1986) died of asphyxiation)
what are lahars
volcanic mudflow
depends on slope and volume
triggered by rainfall
example of a lahar
columbia:
-Armero was buried by lahar in 1985.
-6 major valleys
-travelled at 60kmhr
-50m deep
-killed 23000
-buildings swept away and buried
What is a jokulhlaup
glacial outburst flood
causes erosion and deposition
large volumes of water
caused by failure of ice dam
example of jokulhlaup
Iceland
EFJ erupted in 2010, roads damaged, bridges and house washed away towns evacuated.
was anticipated though.
