Plate Tectonics Flashcards
Name the 4 basic features of the theory of plate tectonics?
Lithosphere is divided into plates like a jigsaw
The plates move in relation to each other
Plates are created from molten material (magma) coming to the surface and plates are destroyed elsewhere
Plates are made by different types of rock
What is the distance of the Lithosphere and the Asthenosphere from the surface?
1-100 km and 1-300 km
What was the distance in km from the surface from the mantle?
600-2900 km
What was the distance in km from the surface of the outer and inner core?
5100,6375
Describe the Core
Very dense, very hot, inner core solid, outer core liquid, source of geothermic heat
Describe the mantle
Solid, dense, heat from the core moved through it part of it (asthenosphere) is neither solid nor liquid plastic
Define the crust
Outermost layer, low density, easily folded+fractured,very variable in thickness
Define the lithosphere
Crust+upper part of mantle, low density, relatively brittle, separate plates, 2 types of lithosphere- oceanic and continental,plates can be one or both, very thin under the oceans, very thick under continents
Define the Asthenosphere
Part upper mantle,higher density than lithosphere, liquid plastic, it can move/deform has convection currents which drives the movements of plates. Where convections diverge lithosphere is created when converge it is destroyed
Name some features of the oceanic plate
Basalt rock, thin 1->10 km, dense, younger, more active, more flexible
Name the features of an continental plate
Granite rock, thicker 10->100km, less dense, older,less active, relatively flexible
What is converging ?
When somethings are moving together
What is diverging?
When some things are moving apart
What defines what happens at the plate boundaries?
The movements of the plates
What occurs at plate boundaries?
Earthquakes
Where are volcanoes in relation to the plates?
Mostly along boundaries, but not all. Most concentration around the Pacific Ocean called the “ring of fire”
Describe a constructive margin
Divergent plates: new lithosphere being created
- magma rising
Name an example of the plates in a constructive margin
North American + Eurasian plates
Atlantic Ocean
Are earthquakes created at a constructive margin?
Yes- generally low magnitude frequent caused by magma rising
Are there volcanoes at constructive margins?
Yes-new crust created, effusive (non-explosive) produces lots of lava
What is the earths crust officially called?
Lithosphere
Describe a destructive subduction zone margin
Convergent plates: oceanic+continental crust
Give an example of a destructible subduction zone
Nazca plate (o)+ S.American plate (c) W.Coast of S.America
Are here earthquakes at a destructive subduction zone?
Yes- high/v.high magnitude most of them highest recorded earthquakes,infrequent
(Chile 1960,9.5)
Are there volcanoes at destructive subduction zones?
Yes-v.explosive produces lots of ash,pyroclastics,gas etc.
Little lava ,often blows the top off mountain
Describe an destructive island arc
Convergent plates, involves 2 oceanic plates
Give an example if an island arc boundary
Caribbean+N.America plates
Both oceanic in the Antilles (W.Indies)
What are the earthquakes and volcanoes at island arcs compared to subduction zones?
They are same
Describe a collision zone margin
Convergent plates: 2 continental plates
Give an example of a collision zone plate margin
Indian+Eurasian plates
Both continental in N.Indian (Himalayas)
Are there earthquakes at collision zones?
Yes- any magnitude but the highest, higher the magnitude the less frequent
Are there volcanoes at collision zones?
Yes- not explosive,produces lava and fire fountains although very little activity
Describe a constructive plate margin
Two plates sliding side by side- any type of plates
Give an example of a constructive margin
N.American+Pacific plates
California (San Andreas Fault)
Are there earthquakes at constructive plate margins?
Yes-very frequent, but occasionally high magnitude such as 1906 San Francisco earthquake at 8.0
Are there any volcanoes at constructive plate margins?
No
Describe a oceanic hot spot
Plume of magma very close to the surface in the centre of an oceanic plate
Give an example of an oceanic hot spot
Hawaiian Islands in the centre of the pacific plate
Oceanic
Are there earthquakes at oceanic hot spots?
Yes- due to rising magma but low magnitude and infrequent
Do volcanoes occur at oceanic hot spots?
Yes- produces very large volume of “running lava” continuous activity
Describe a continental hot spot
Plume of magma very close to the surface in the centre of a continental plate
Give an example of an continental hot spot
Yellowstone Park
Centre of the N.American plate
Do earthquakes occur at continental hot spots?
Yes- infrequent and moderate magnitude (5-6.5)
Do volcanoes occur at continental plate boundaries?
Yes- very infrequent, but massive, super volcanoes producing different types of lava some runny some not
Where are subduction zones found?
Constructive and destructive plate margins
E.g West coast of South America
What does the oceanic plate do at a subduction zone?
As it is denser so it sinks beneath the continental plate this is called subduction
What does the oceanic plate do to the seabed to form what?
Ocean trench
What does the oceanic plate take down with it in a subduction zone and what does it do?
Sea water and it lowers the melting point of the subduction point
Do the two plates in a subduction plate slide by each other easily and what happens?
They do not slide past easily and when it becomes too great there is a sudden jerk which causes an earthquake
What is the place where the melting occurs?
Benioff Zone
What happens to the continental plate in a subduction zone?
The continental plate is less dense and crumples forming fold mountains
What happens when the oceanic plate sinks?
It causes the oceanic plate to melts
What do the molten rocks form? And what are the properties of that thing?
Plutons, they rise through the continental plate
The new magma is very light and full of gas
What do plutons create when they reach the surface? And what kind of them are they?
Volcanoes- they are very violent as there is so much gas
What happens when a pluton solidifies?
They form huge masses of granite which may get exposed when the overlaying rocks are eroded away
Name the first stage of a constructive plate margin
Convection currents in the asthenosphere
Name the second stage of a constructive plate margin
Tension causes the lithosphere to stretch and thin magma pushes up and causes the lithosphere to bend upwards
Name the third stage of a constructive plate margin
The lithosphere eventually fractures along two lines and part of it sinks creating a rift. Magma reaches the surface through the fractures
Name the fourth stage of a constructive plate margin
The lithosphere is now wider. The magma stops rising and lava forms. The process is repeated many times and the ocean gets wider and wider
What happens when the gap in the constructive plate margin widens?
Magma reaches the surface and forms new rock. Usually starts beneath land but eventually a ocean basin forms with the land moving away on either side
Give an example of an ocean basin
Mid-Atlantic Ridge
Where is the northernmost part of the Mid-Atlantic Ridge?
Iceland
Does volcanic activity and earthquakes occur on the Mid-Atlantic Rift?
Yes- volcanoes: non explosive (effusive)
Yes-Earthquakes: low magnitude events
What are the main features of a subduction plate margin?
Ocean trench,fold mountains,earthquakes (highest mag.)
Volcanoes: lava,pyroclastic flows,ash,Lahars
What type of lava is produced at a volcano at a subduction zone?
Very thick (viscous), non-runny, travels only short distances
What are volcanoes like at a subduction zone?
Very explosive,often destroy part of the mountain
What are pyroclastic flows like at subduction zones?
Mass of gas,ash,large lumps of lava travelling at up to 200km/h at up to 200C
What is ash?
Pulverised rock from the mountain, can be up to 20 km high
What are Lahars?
Volcanic mudflows formed when ash mixes with water ( melting ice cap, or a rain storm) moving at up to 100km/h
How is a island arc formed?
One oceanic plate sub ducts under another oceanic plate. The non-subducting plate doesn’t fold. Volcanoes occur forming a curving line of Islands e.g W.Indies
How is a collision zone margin formed?
Starts as a subduction zone and slowly the ocean basin which is a oceanic lithosphere (ol) becomes narrower. Eventually there is no (ol) left and 2 (cl) collide and crumple forming fold mountains.
Do earthquakes and volcanoes occur at collision zones?
A lot of activity when the subduction is occurring but as it stops far less volcanoes more earthquakes including v.high magnitude
Give an example of a collision zone
Himalayas and the Tibetan plateau
What can a collision margin create?
A depression. E.g Ganges depression
What happens at a conservative plate margin?
Two plates slide past each other but there is no vertical moments
Give an example of a conservative plate margin
San Andreas fault line
What are the two plates at the San Andreas fault line and why is there friction?
N.American plate and the Pacific plate. They travel the same direction but the N.American plate travels slower and creates the illusion it is travelling in the opposite direction
What magnitudes are earthquakes at hot spots?
Low magnitude
How are volcanoes created at hot spots?
A magma plume is very close to the thin lithosphere
What is volcanic activity like on the big island in Hawaii?
Continuos but not explosive, fire fountains (clumps of lava thrown into the air) and fast-flowing lava
Does the Hawaiian hot spot move over time?
No- the Pacific plate moves NW, looks like it moves SE. Due to the location volcanic activity only occurs on the big island. The northern islands are smaller due to thermal contraction,erosion ams landslides
What are the two main causes of earthquakes?
Movement of crust at fault lines e.g plate boundary (large mag.)
Movements of magma under lithosphere (smaller mag.)
What are the 4 types of seismic waves?
P,S,L,R waves
What do movements in plates cause?
Seismic waves
What is the point where a earthquake occurs?
Focus
What are earthquakes measured by?
Seismometer
What is a seismometer connected to and what does it produce?
Seismograph and it produces a time-based trace of the movement.
What is the trace from a seismograph called?
Seismogram
What can be used to locate the epicentre of an earthquake?
P and S waves travel at different rates
What is the formula to locate the distance from an earthquake?
Time in seconds between the arrival of the P and S waves x 8
= distance in km to the epicentre (approx.)
What is the minimal amount of seismometers needed to pinpoint a epicentre?
3
What are the two scales for earthquakes called?
Richter and Mercalli
An increase of 1 on the Richter scale = how much more energy released ?
30x
What is the Richter scale based on?
The amount of energy released
Is the Richter scale finite or infinite?
Infinite
What is the Mercalli scale based on?
Observation of damage that occurs
Is the Mercalli scale finite or infinite?
Finite, 1 to 12
Are the two scales for earthquakes related and if so to what use?
Yes- to asses possible impact which is valuable in formation for rescuers etc.
What was the date of the Kobe Earthquake?
17th January 1995
Why was the Kobe earthquake happening at 5:46 significant?
People are travelling in their cars (rush hour), more death as more people
What was the magnitude and duration of the Kobe earthquake?
7.2 and it lasts for 20 seconds
Name the primary impacts at the Kobe earthquake
200,000 buildings collapsed, many trains derailed
1km of Hanshin Expressway and 130km of bullet train bridges collapsed. 120 of 150 quays in main port destroyed
What were the two plates involved in the Kobe Earthquake?
Philippine plate and Eurasian plate
Secondary effects of the Kobe earthquake
Electricity/gas/water supplies disrupted, fires destroyed 7500 houses from electricity mains and broken gas pipes. Gridlock roads,delayed emergency services.230,000 made homeless
716 aftershocks, Mitsubishi and Panasonic closed
What happened at the Kobe earthquake?
Philippine plate is forced down on contact with the Eurasian plate. This is issued a very big earthquake after a long time of friction etc.
What were the long term effects of the Kobe earthquake?
Central areas and commercial rebuilt but worst affected had little rebuilding.
New buildings are made earthquake proof by concrete frames,reinforcing bars and steel frames
No buildings built on clay as liquefies causing collapse
How are fold mountains formed?
Two continental plates collide with enough force to crumple the lithosphere
How can a volcano help a person who lives close to them?
Farming as rich land from volcano
Minerals and rocks can be used or sold
Create jobs for the tourism created
What type of place would be effected by a volcano?
Ski resort
