Tectonic Processes (PHYSICAL) Flashcards
[Convergent (destructive)] Oceanic meets Continental
- create high magnitude earthquake.
- very explosive volcanoes (composite).
- oceanic (denser) plate subducts beneath continental plate.
- friction + pressure build up in the Benioff Zone.
- fold mountains + oceanic trenches.
[Convergent (destructive)] Oceanic meets Oceanic
- subduction. One more dense than other. Denser one subducts.
- volcanic islands, ocean trenches, earthquakes, tsunamis.
- island arcs.
[Convergent (destructive)] Continental meets Continental
- pushing up against each other and folding up instead of subducting.
- crumpling faults.
- fold mountains.
- sometimes subduction can occur causing an earthquake (shallow).
[Divergent]
- 2 plates moving apart creating new crust.
- volcanoes form.
- submarine volcanoes.
- minor shallow focus.
- mid-ocean ridges.
- rift valley.
- crust is stretched and breaks into sets of parallel cracks. Land between fault collapses.
[Conservative]
- 2 plates slide past each other.
- results in a major break (fault) between crust, known as transform fault.
- earthquakes -> shallow focus as plates get stuck causing stress and pressure to build which is suddenly released.
[Intra-Plate(Earthquakes)]
- occur in middle or interior of tectonic plates.
- occur along old fault lines which reactivate.
- collision of tectonic plates can also fracture the crust well away from the boundary (E.g. the Tibetan Plateau).
[Intra-Plate(Hotspots)]
- results of upwelling of hot molten material from core/mantle. E.g. Kilauea, Hawaii.
- high heat and lower pressure at the base of the lithosphere enables melting of the rock.
- magma rises through cracks in the crust and erupts.
- as the plate moves over the stationary hotspot, new volcanoes form and a chain of islands like Hawaii.
Earth’s Structure
- Inner Core -> solid iron, hottest (6000 degrees).
- Outer Core -> semi-molten. Liquid iron + nickel. (4500-6000 degrees).
- Mantle -> upper part is solid but below is molten and forms the asthenosphere on which the plates float. Widest layer.
- Lithosphere -> crust + upper mantle.
- Crust -> Outer shell. Solid rock.
Continental Plates: older, thicker, made of granite and are less dense (45-50km). Make up earth’s landmasses.
Oceanic Plates: thin (6-10km) and denser, made of basalt and line ocean floors.
Ocean Trenches
Where subduction takes place. Oceanic plate pushing under Continental, creating trench.
Fold Mountains
Crumpling/pushing up of Continental plates. Tends to happen when Continental meets Continental.
Benioff Zone
Where subduction is happening in the crust. Friction builds.
Sub-marine Volcanoes
Volcanoes that occur on the sea bed. Occurs on divergent boundaries and hotspots. Made from convergent (oceanic-oceanic)
Island Arcs
Arc of volcanic islands caused by oceanic-oceanic convergent.
Intraplate
In the middle of the plates not the boundary.
Subduction
One plate going under/subducting under another.
Convection Currents
- radioactive decay of some elements in the mantle and core generate a lot of heat.
- when lower parts of the asthenosphere heat up they become less dense and slowly rise.
- as they move towards the top they cool down, become more dense and slowly sink.
- circular movements are called convection currents.
- convection currents create drag on the base of the tectonic plates which cause them to move.
Slab Pull
- force that results from denser oceanic plates sinking beneath less dense Continental plates along convergent boundaries and subduction zones.
- descending plate pulled by gravity through mantle asthenosphere which is hotter and less rigid.
Sea-Floor Spreading
Molten material (basalt) oozing up from Earth’s mantle along mid-ocean ridges. Creates new sea floor which spread away from the ridge in both directions.
Paleomagnestism
Study of Earth’s magnetic field in rocks.
Subduction Zone (convergence)
-> high magnitude quake but deeper focal depth.
-> high explosive eruptions.
Convergence (Continental Plates)
-> low magnitude quake but shallow focal depth.
