2 + A. Tectonic Plates Flashcards
What are the key features of Continental crust?
Continental crust is:
- located below land masses and shallow seas
- 30-60 km thick
- made of old rocks (granite)
- is less dense than oceanic crust
What are the key features of Oceanic crust?
Oceanic crust is:
- Located below deep ocean
- 5-8km thick
- made of young rocks (basalt)
- denser than continental crust
What causes tectonic plates at plate boundaries to move?
Tectonic plates are moved by sub-crustal convection currents in the mantle.
Draw a diagram of a divergent (constructive) plate boundary:
The diagram should feature:
- Mantle
- Reference to sub-crustal convection currents
- Reference to two tectonic plates (Eurasian vs North American for Iceland) being pulled apart
- Volcanic island / Shield Volcano / volcanic ridge in gap between plates
What types of volcanoes form at divergent (constructive) plate boundaries?
Types of volcanoes at divergent (constructive) plate boundaries:
- Shield volcanoes (broad and flat) formed by viscous and slow-moving lava:
- Volcanic islands + Underwater volcanic ridges
What strength are earthquakes along divergent (constructive) plate boundaries?
Earthquakes along divergent (constructive) plate boundaries are weak.
In Iceland:
- Most are under 3.0
- Strongest earthquake 17th May 2000 at magnitude 6.5 on Richter scale.
Besides volcanoes, what types of landforms form at divergent (constructive) plate boundaries?
Types of landforms at divergent (constructive) plate boundaries:
- Oceanic ridges
- Rift valleys
- Transform faults
- Fracture zones
Give two examples of landforms on a divergent (constructive) plate boundary:
Mid-Atlantic Ridge
Surtsey, Iceland
Draw a diagram of a convergent (destructive) plate boundary:
The diagram should feature:
- Mantle
- Reference to sub-crustal convection currents
- Reference to two tectonic plates (Eurasian versus Phillipine Plate for Japan) being pulled together
- Reference to denser oceanic crust subducting under less dense continental crust
- Steep composite volcano
- Ocean trench (gap between plates)
- Display of magma from end of oceanic crust rising though volcano
What types of volcanoes form at convergent (destructive) plate boundaries?
Steep composite volcanoes form at convergent (destructive) plate boundaries, which are tall and have explosive eruptions.
What strength are earthquakes along convergent (destructive) plate boundaries?
Earthquakes along convergent (destructive) plate boundaries are fairly strong!
In Japan:
- The average earthquake strength is 3.76
- Strongest earthquake 11 March 2011 at magnitude 9.1 on Richter scale
Besides steep composite volcanoes (mentioned on another card), what types of landforms form at convergent (destructive) plate boundaries?
Types of landforms at convergent (destructive) plate boundaries:
- Fold mountains
- Volcanic cones
- Volcanic island arcs
- Ocean trenches
Give two examples of landforms on a convergent (destructive) plate boundary:
Mt Fuji (Japan)
Japan Trench (you’ll never guess where ¬_¬ )
Draw a diagram of a transform / conservative plate boundary:
The diagram should feature:
- Two continental plates
- Arrows showing direction of movement along each other, either opposing or at different speeds.
- Mantle (underneath diagram)
- (River bent by fault between the two)
What types of volcanoes form at transform / conservative plate boundaries?
Trick question - none! No volcanoes form on transform / conservative plate boundaries as no magma rises.
What strength are earthquakes along transform / conservative plate boundaries?
Earthquakes along transform / conservative boundaries are pretty strong!
In the SW USA:
- There is, on average, a magnitude 6.0 earthquake every 22 years.
- Strongest earthquake 1907 magnitude ~7.9 on Richter scale.
What type of landform forms at transform / conservative plate boundaries?
Fault line
Give an example of a fault line on a transform / conservative plate boundary:
San Andreas Fault, USA (Pacific ^^ vs North American Plate ^ )
Draw a diagram of a convergent (collision) plate boundary:
The diagram should feature:
- Mantle
- Reference to sub-crustal convection currents
- Reference to two tectonic plates (Eurasian vs Indian for Himalayas, Eurasian vs African for Alps) being pulled together
- Reference to crumpling / puckling of rocks as they collide
What types of volcanoes form at convergent (collision) plate boundaries?
Trick question - none! No volcanoes form on convergent (collision) plate boundaries as no magma rises.
What strength are earthquakes along convergent (collision) plate boundaries?
Earthquakes are infrequent but they can be powerful!
In the Himalayas:
- Average earthquake strength magnitude 7 on Richter scale (but infrequent)
- Strongest earthquake 1950 at magnitude 8.7 on Richter scale
What type of landform forms at convergent (collision) plate boundaries?
Fold mountains
Give two examples of fold mountains on convergent (collision) plate boundaries:
The Alps, Europe:
- African Plate→ ←Eurasian plate
Himalayas, Asia:
- Indian Plate→ ← Eurasian plate
How do sea floors spread?
- Rocks partially melt in the upper mantle
- The resulting magma forms pockets which collect together and rise to the surface
- Magma is extruded along the ridge
- Lava cools rapidly in contact with sea water to form new lithosphere, which diverges from the ridge due to sub-crustal convection currents
How does fossil evidence support continental drift?
- Similarity of fossils found on matching coastlines of South America and Africa - impossible for the species found to swim across the Atlantic Ocean!
- Fossils of tropical plants in Antartica suggest that it must have once been situated closer to the Equator where lush-swamp-like flora could grow
How do glacial deposits support continental drift?
- Permo-carboniferous glacial deposits in Africa, South America and India suggest that these continents might have been joined when glaciation occured.
How do coastlines support continental drift?
- Coastlines match like a jigsaw when fitted together, especially Africa and South America.
- Orogenic mountain belts of the same age - the Appalacian Mountains, Scottish Highlands and Scandinavian mountains join to create a continuous mountain range when the Atlantic coastlines are fitted together.
- Precambrian rocks (same age) on either side of the Atlantic also join up when the Atlantic coastlines are fitted together
What evidence is there for sea floor spreading?
- Rocks become progressively older with increasing distance from ridge crest
- Thickness of sediment increases with increasing distance away from the ridge - more time for sediment to accumulate
- Paleomagnetism - new rock has normal polarity but older rock consists of polarised stripes (same on both sides of the ridge)
