Plate tectonics Flashcards
who came up with the continental drift theory
Alfred Wegener
Continental Drift Theory
that the continents used to form one supercontinent but began to drift a part into their current positions
when was continental drift widely accepted
1950
why was the theory of continental drift NOT taken seriously at first
because there was no mechanism that could be explained
what were the two large portions that made up Pangaea
- Laurasia
- Gondwanaland
what happened to the continents 135 MYA
separated to more present shape WITHOUT separating too much
what did the continents look like 65 MYA
began to break apart from each other to be located in the present day locations
polar position
focused on the latitudinal position as a cause of the glaciation of continents = ice sheets should appear on continents when they are located at polar or near-polar latitudes.
describe polar position of the continents 440 MYA
polar position - yes
ice sheets - yes
describe polar position of the continents 390 MYA
polar position - yes
ice sheets - no
describe polar position of the continents 300 MYA
polar position - yes
ice sheets - yes
describe polar position of the continents 260 MYA
polar position - yes
ice sheets - yes
do the location of continents and whether they are together or separate affect weather
YES
where is slow flow
in the upper mantle
what drives slow flow and continent movements
convection cells
steps within the convection cells
- heating of the material in the mantle
- the hot material rises
- begins to move outwards
- cools
- eventually there will be collisions and subduction
how does the gravity push/pull affect plate tectonics
lava is pushed up while the weight of thickening plate is pushed down
curst formation steps
- material from the asthenosphere upwells along the sea floor and becomes extrusive igneous rock
- the oceanic crust is subducted under the lighter continental crust
- the subducted oceanic crust begins to melt
- melting generates magma = forms igneous intrusion rock and extrusive explosions
what is the range of speed for the movement of continents
from 1 to 12cm per year
how can the movement of continents differ
- in their speed
- in their direction
- in their orientation
what is the Wilson cycle focused on
the different formations of supercontinents in the past
how many supercontinents were expected to have been formed in 3 billion years (Wilsons cycle)
5
supercontinents act as
insulators - their mass traps geothermal heat in earth
what are the 4 steps in the Wilson cycle
- assembly
- stability
- splitting
- reassembly
average Wilson cycle takes ____ years
500 Million
does assembly in the Wilsons cycle have to be complete
NO- it can be incomplete
3 main types of plate boundaries
- convergent
- divergent
- transform
divergent plate boundary
plates move AWAY from each other
convergent plate boundary
plates move TOWARDS each other
transform plate boundary
plates move in OPPOSITE directions but they REMAIN together
types of convergent plates
- convergent oceanic plates
- convergent continental plates
- convergent oceanic AND continental plates
convergent plates results in _____
subduction
convergent OCEANIC plates results in
volcanic expression
convergent CONTINENTAL plates results in
formation of mountains (such as the Himalayas)
convergent of OCEANIC AND CONTINENTAL plates results in
volcanic activity
divergent CONTINENTAL plates results in
rift valleys and sometimes divots
TRANSFORM plates can be identified by
- ridges not lining up
3 main STRESS types of crust deformation
- tension
- compression
- shear
crust deformation
tension AKA
stretching
crust deformation
compression AKA
shortening
crust deformation
shear AKA
twisting
the stress of curst deformation results in
STRAIN
two examples of strains caused by crust deformation stress
- folding (bending)
- faulting (breaking)
what causes folding
compression at convergent plates
what are examples of the result of folding
basins and domes
anticlines and synclines in folding
the up and down folds that usually occur together and are caused by compressional stress
anticlines vs synclines of folding
Anticlines
folds in which each half of the fold dips away from the crest.
Synclines
folds in which each half of the fold dips toward the trough of the fold.
shear stress
shear stress results in
fault and bending horizontally
compression
compression results in ____ surface expression(s)
- folding
- faulting
tension
tension results in _____ surface expression
thining crust
what causes faulting
forces on both sides of a plate that causes fracture of material (break)
what are three examples of faulting
- normal fault
- thrust fault
- strike-slip fault
what causes a normal fault
tension
how do identify a normal fault
when the hanging-wall side is displaced DOWNWARDS
what causes a thrust fault
compression
how to identify a thrust fault
the hanging-wall side moves UPWARD
what causes a strike-slip fault
shearing (twisting)
how to identify a strike-slip fault
have offset on the surface (ex. ridge lines DON’T line up)
is there vertical displacement in a strike-slip fault
NO
what fault is caused by diverging forces
normal fault
what fault is caused by converging forces
reverse/thrust fault
what fault is this
reverse/thrust fault
what fault is this
normal fault
what fault is this
strike-slip fault
orogenesis
mountain generation
examples of orogenesis
- folding and faulting
- plate collisions
- addition of terranes
- volcanic addition
- uplift
what are some examples of plate interactions that cause orogenesis
- continent to continent
- ocean to continent
- ocean to ocean
three mountain ranges formed by orogenesis
- rocky mountains
- Appalachians
- Himalayas
what mountain range is this
Rocky Mountains
what mountain range is this
Appalachians
what mountain range is this
Himalayas
earthquakes are a
series of shocks caused by movement in the crust OR upper mantle
where do earthquakes often happen
along fault lines
center of earthquake movement
focus
where is the point of failure when referring to earthquakes
the focus
what is the point on the surface ABOVE the focus in an earthquake
epicenter
how are earthquakes ordered
on a scale of magnitude with each increase in level representing 10 times the strength
compare a magnitude 6 earthquake to a magnitude 5 earthquake
6 is 10 times STRONGER then a 5
aftershocks refer to the
further slippage along fault lines (for earthquakes)
how do we record earthquake magnitudes
with seismographs
volcanoes have molten rock from the
asthenosphere
steps in a volcanic eruption
- magma is expelled from underground (becomes lava) where it is still molten
- gases and pyroclastics are also ejected
how many active volcanoes are there in the world
550
where are volcanoes (3 locations)
- subduction boundaries
- sea-floor spreading centers
- hot spots
what kind of volcanic location is Iceland
a hot spot AND a plate boundary
the type of volcanic activity is dependent on
the magmas chemistry (make up( and viscosity
two types of volcanic ACTIVITY
- effusive
- explosive
effusive volcanic activity
- low viscosity magma
- with less than 50% silicon while rich in iron and magnesium
effusive or explosive volcanic activity
Gentle with lava pouring onto the surface with small explosions
effusive
effusive or explosive volcanic activity
found in sea-floor spreading and hot spots
effusive
effusive or explosive volcanic activity
dramatic with explosions made from built-up gases, lava and pyroclastics
explosive
effusive or explosive volcanic activity
are found in subduction zones
explosive
explosive volcanic activity
- high viscosity magma
- 50 to 75% silicon and high in almunium
types of volcanoes
- shield volcano
- composite cone volcano
- cinder cones
- caldera
caldera is a
steep-sided, circular depression
which type of volcano is this
collapsed volcanic cone
caldera
Cinder cones
small features and made mostly from loose tephra (volcanic ash)
what type of volcano is this
built around single vent
cinder cones
what type of volcano is this
lava flow is rare
cinder cones
what type of volcano is this
steep sided
cinder cone
what type of volcano is this
steep and high elevations
composite cone volcanoes
what type of volcano is this
very symmetrical
composite cone volcanoes
what type of volcano is this
happen in subduction zones
composite cone volcanoes
what type of volcano is this
a very explosive volcano
composite cone volcanoes
what type of volcano is this
made from basaltic lava
shield volcanoes
what type of volcano is this
less violent volcano
shield volcano
what type of volcano is this
associated with hot spots and spreading zones
shield volcanoe
what type of volcano is this
large horizontal dimensions
shield volcanoes
what type of volcano is this
have gentle slopes
shield volcanoes
what type of volcano is this
Shield volcano
what type of volcano is this
shield volcano
what type of volcano is this
Composite cone volcano
what type of volcano is this
composite cone volcanoe
what type of volcano is this
cinder cone
what type of volcano is this
Caldera
what plate is ALWAYS subducted in a subduction
ocean plate - it is always heavier
what happens to the crust in a transform
it is NOT created NOR destroyed
what type of plate boundary interaction results in the old crust being destroyed
convergent
what type of plate boundary interaction results in new crust being created
divergent
what is the force that affects on object
stress
force where landforms RESULT from the stress
strain
two types of strain
folding and faulting
3 types of stress
- tension
- compression
- shear
foreshock of an earthquake
movement BEFORE the main shock
aftershock of an earthquake
movement AFTER the main shock
p waves in an earthquake
faster and low impact that move like an accordion
s waves in an earthquake
slower and more destructive that move like a wave
what is the significance of the different waves seen in an earthquake
Different waves allow us to know the composition of the center of the Earth
where does a volcano form
at the end of a vent
where are craters found
near the summit of a volcano
pyroclastic flow
air borne rock and rock fragments from vent
what is the name for a pyroclast on the ground
tephra
what forms from pyroclastic flows near a vent
cinder cones
do cinder cones have lava
NO
what is a hot spot and give an example
volcano forms but it is NOT at a plate boundary (example would be Hawaii)
2 types of explosions in volcanoes
- effusive
- explosive
what type of explosion is this
low viscosity magam
effusive
what type of explosion is this
forms gentle sloping craters or volcano
effusive
what type of explosion is this
found at cinder cones, shield volcanoes and plateau basalt
effusive
what type of eruption is found in ocenas
effusive
what type of explosion is this
high viscosity lava
explosive
what type of explosion is this
found in composite volcanoes
explosive
example of a shield volcano
in Hawaii
example of a composite volcano
- St Helens
- Pompeii
- Japan