Topic 1 - Tectonic Processes And Hazards Flashcards
How many tectonic plates are there in total?
52 (7 main major tectonic plates and 8 main minor tectonic plates)
Name the 7 major tectonic plates.
African plate Antarctic plate Eurasian plate Indo-Australian plate North American plate South American plate Pacific plate
Name the 8 main minor tectonic plates.
Nazca plate Philippine plate Caribbean plate Cocos plate Arabian plate Juan de fuca plate Scotia plate Indian plate
Name examples of micro plates.
Somalian in East African Rift Valley
Sundar in Indonesia
Iranian and Iberian in the Middle East
How was the earth formed and differentiated into layers?
- Dust condensed out of solar nebula (hydrogen and helium clouds) through accretion
- Dust particles started to assemble into larger particles through electrostatic attraction creating large enough object to have own gravity = primitive earth (homogenous mixture)
- As planetesimals (small pieces of matter) crashed into primitive earth, motion energy converted to heat and radioactive elements disintegrated spontaneously releasing energy which was absorbed by surrounding matter and converted to heat
- Melting of earth due to heat brought lighter (H and He) materials to outer layers of earth and brought interior heat to surface where it could radiate into space
- Earth started to cool and solidify (oldest rock first e.g. Granite)
- Melting initiated escape if lighter gases from interior leading to formation of atmosphere and oceans
- Interior of earth melted to ‘soft’ state in which components moved around with heavy material e.g. Iron sinking to centre and lighter material floating upward towards crust
- This is called differentiation
How do you layout an answer to a describe question?
Use PDA
P - pattern - state the pattern that you are asked to describe
D - detail - include examples and data from the source given
A - anomalies - state the anomalies that don’t fit the pattern you are asked to describe
Oceanic to Continental Convergence (Destructive plate boundary)
- Explain the tectonic activity.
- oceanic plate and continental plate converge (move towards each other)
- denser oceanic plate subduct beneath less dense continental plate where it partially melts and becomes molten in subduction zone
Oceanic to Continental Convergence (Destructive plate boundary)
- State the landforms and activity.
Landforms:
Fold mountains (sedimentary and metamorphic rock)
Ocean trench
Volcanic arcs
Composite volcanoes
Activity:
- Shallow, intermediate and deep focus earthquakes along wadati Benioff zone with 8-9 magnitude
- Composite volcanoes (700km from trench) with andesitic magma with explosive infrequent eruptions VEI scale of 5-6
Oceanic to Continental Convergence (destructive plate boundary)
- Name examples for this plate boundary.
- Andes (fold mountains)
- Peru-chile ocean trench (Nazca plate subducting under South American plate)
- Japan 2011 earthquake and tsunami (magnitude 9 with focus 24km deep)
Oceanic to oceanic Convergence (destructive plate margin)
- Explain the tectonic activity at this plate margin.
- Two oceanic plates converge (move towards each other)
- the older, cooler and denser plate is subducted beneath younger more buoyant plate
- older plate partially melts due to hydration melting
- subduction causes low density floor sediment to accumulate off surface of ocean floor and thrown into beach - obduction
Oceanic to oceanic Convergence (destructive plate margin)
- state the volcanic activity and landforms.
Landforms: Bathymetry - obduction Volcanic island arc Wedges (accretionary) Oceanic trench Back arc and fore arc zones Activity: - shallow to intermediate foci earthquakes with moderate to high magnitude of 7-9 - composite volcanoes due to hydration melting
Oceanic to oceanic Convergence (destructive plate boundary)
- state examples for this plate boundary.
- Montserrat 2010 and 1995 eruptions
- Caribbean Islands (island arc)
- Aleutian Islands (island arc)
Continental to Continental Convergence (collision plate boundary)
- Explain the tectonic activity.
- two Continental plates converge (move towards each other
- both have equal buoyancy so neither subduct
- pressure and force causes plate sediment to be forced upwards to buckle into anticlines and synclines
Continental to Continental Convergence (collision boundary)
- state the activity and landforms.
Landforms: Fold mountains Activity: - typically shallow focused earthquakes with moderate magnitude 6-8 - no volcanic activity as no subduction
Continental to Continental Convergence (collision boundary)
- state examples for this boundary.
Himalayas mountains (fold mounstains) Eurasian and indo- Australian plate margin
Gujarat, India earthquake 2001
Sichuan, China earthquake 2008
Divergent (constructive) plate boundary
- explain the tectonic activity.
- Two plates of the same type diverge (move apart) due to conversion currents and buoyancy force
- known as sea floor spreading
- symmetrical alignment
Divergent (constructive) plate boundary
- state the activity and landforms.
Landforms:
Ocean ridges with Rift Valley and faulting at right angles
Volcanic arc
Underwater mountains
Activity:
-shallow focus earthquakes with low magnitude of 5-6
- volcanoes due to decompression melting made from basaltic lava with low VEI of 1-3 (effusive)
Divergent (constructive) plate margin
- state examples for this plate margin.
Mid- Atlantic Ridge (ocean ridge) Eurasian and North American plate margin
Mid Indian Ocean ridge (ocean ridge)
East Pacific rise (ocean ridge)
African Rift Valley (two continental plates)
Iceland formed by mid Atlantic ridge (formed due to hot spot also)
Transform (conservative) plate boundary
- explain tectonic activity.
- two plates (same or different) move past each other at different speeds in either the same direction or opposite direction
- as they slide past each other they build up and release energy suddenly
Transform (conservative) plate boundary
- state activity and landforms.
Landforms:
Ridges and scars on rock mainly on ocean floor
Activity:
- shallow focus earthquakes with moderate magnitude of 6-8
- no volcanoes as no subduction
Transform (conservative) plate boundary
- state examples for this boundary.
San Andreas fault
Describe the structure and formation of oceanic crust
- thin (7km thick)
- more dense (3.3g/cm^3)
- made of basalt
- youngest - less than 200 million years old
- form from sea floor spreading
Subducts beneath other lithosphere
Describe the structure and formation of continental crust
- thick (up to 70km thick)
- less dense (2.7g/cm^3)
- made of granite
- oldest - 1500+ million years old
- an amalgamation of rock originally formed at volcanic arcs and hotspots and then it passed through rock cycle, mountain building, erosion and sedimentation to form lithosphere today
- does not subduction under other lithosphere
Describe the earths lithosphere
- contains crust and uppermost layer of the mantle
- made of 52 tectonic plates
- thickness: oceanic (7km) to Continental (70km)
- surface temp of up to 400 degrees c
- density: oceanic (3.3g/cm^3) continental (2.7g/cm^3)
- composition: oceanic (basalt) continental (granite)
- physical state is solid
Describe the mantle of the earths structure.
- consists of asthenosphere (upper mantle) and mesosphere (lower mantle)
- thickness 700-2890 km
- density 3.3-5.4g/cm^3
- physical state of plastic solid allows to flow
- composition: peridotite, upper (olivine), lower (magnesium silicate)
- temperature of 870 degrees c with gradient
- 2 mantle plumes
- convention currents occur
Describe the structure of the outer core of the earth
- depth 2890-5150 km
- density 9.9 - 12.3g/cm^3
- composition 12% sulphur 88% iron
- 4400- 6100 degrees c
- physical state is liquid
- generates magnetic field
- convection currents occur
Describe the structure of the inner core of the earth
- depth 5150km -centre
- density 13.5g/cm^3
- composition 20% nickel 80% iron
- temperature 7000 degrees c
- solid (possibly two parts with crystals aligned in opposite directions)
What we’re the late 19th century theories on tectonics?
contraction of the earth due to cooling
- explains compressional features (fold mountains)
- doesn’t explain extensional features (rift valleys)
- couldn’t explain shapes and positions of continents
Expansion of earth due to heating
- explains why continents are broken up and explains extensional features
- couldn’t explain compressional features
What was Sir Francis Bacons addition to the plate tectonics theory (1620)?
Noted similarities of shorelines of eastern South American and Western Africa but did not propose they were once connected
What was Edward Suess’ addition to the plate tectonics theory? (Late 1800s)
Noted similarities of fossils in India, Australia, Africa, South America and Antarctica and evidence for glaciation on these land masses
What was Frank Taylor’s addition to the plate tectonics theory? (1910)
Explained formation of mountain ranges due to movement of continents
What was Alfred Wegeners theory of continental drift?
Published his theory in his book The Origin Of Continents and Oceans in 1912
All continents were once connected as one landmass called Pangaea
200 million years ago Pangaea divided into Laurasia (North America and Eurasia) and Gondwanaland - splits into India, sour America, Australia, New Zealand, Antarctica, Africa
Continents moved freely over surface of earth changing position relative to one another
What evidence supports the theory of continental drift?
- biological/paleontological evidence
Mesosaurus fossils - freshwater reptile in Brazil and s. Africa but could not have swam all the way
Lystrosaurus - mammal like reptile - strictly land dweller - fossils found in India, s. Africa and Antarctica
Glossopteris (fern like plant) found in s. America, s. Africa, Australia, India and Antarctica - seeds too big to dispersed by wind/ocean - climatic evidence - glaciation features in India and South America not possible a current locations
Oil in Antarctica which is formed in warm conditions - geological evidence (rock age, type and structure)
Appalachian mountains east USA stop at newfoundlands same age and type as rock in Ireland Britain and Norway - reassembled = nearly continuous mountain range
Geological evidence - jigsaw puzzle - all countries fit together like a jigsaw
Define intra plate activity.
Tectonic activity such as volcanoes and earthquakes that occur within the interiors of tectonic plates which are due to hot spot and mantle plume activity
What we’re the late 19th century theories on tectonics?
contraction of the earth due to cooling
- explains compressional features (fold mountains)
- doesn’t explain extensional features (rift valleys)
- couldn’t explain shapes and positions of continents
Expansion of earth due to heating
- explains why continents are broken up and explains extensional features
- couldn’t explain compressional features
What was Sir Francis Bacons addition to the plate tectonics theory (1620)?
Noted similarities of shorelines of eastern South American and Western Africa but did not propose they were once connected
What was Edward Suess’ addition to the plate tectonics theory? (Late 1800s)
Noted similarities of fossils in India, Australia, Africa, South America and Antarctica and evidence for glaciation on these land masses
What was Frank Taylor’s addition to the plate tectonics theory? (1910)
Explained formation of mountain ranges due to movement of continents
What was Alfred Wegeners theory of continental drift?
Published his theory in his book The Origin Of Continents and Oceans in 1912
All continents were once connected as one landmass called Pangaea
200 million years ago Pangaea divided into Laurasia (North America and Eurasia) and Gondwanaland - splits into India, sour America, Australia, New Zealand, Antarctica, Africa
Continents moved freely over surface of earth changing position relative to one another
What evidence supports the theory of continental drift?
- biological/paleontological evidence
Mesosaurus fossils - freshwater reptile in Brazil and s. Africa but could not have swam all the way
Lystrosaurus - mammal like reptile - strictly land dweller - fossils found in India, s. Africa and Antarctica
Glossopteris (fern like plant) found in s. America, s. Africa, Australia, India and Antarctica - seeds too big to dispersed by wind/ocean - climatic evidence - glaciation features in India and South America not possible a current locations
Oil in Antarctica which is formed in warm conditions - geological evidence (rock age, type and structure)
Appalachian mountains east USA stop at newfoundlands same age and type as rock in Ireland Britain and Norway - reassembled = nearly continuous mountain range
Geological evidence - jigsaw puzzle - all countries fit together like a jigsaw
Define intra plate activity.
Tectonic activity such as volcanoes and earthquakes that occur within the interiors of tectonic plates which are due to hot spot and mantle plume activity
Examples of volcanoes at interplate boundaries.
Convergence oceanic to Continental = mt St. Helens, North America (Juan de fuca and North American plate)
Convergence oceanic to oceanic = souffriere hills Montserrat, North America (South America and Caribbean plate)
Divergence= Eyjafjallajokull Iceland (Eurasian and North American plate with hot spot activity as well)
Examples of volcanoes at intra plate boundaries
Mantle plume = mount nyiragongo, democratic republic of Congo, Africa (African plate mantle plume)
Hot spot = Hawaiian island chain, Pacific Ocean (Pacific plate Pacific mantle plume)
