Plate Techtonics Flashcards
What does the earth’s plate comprise of?
- Core
- Mantle (Lower mantle, Asthenosphere, Uppermost mantle)
- Lithosphere (Uppermost mantle, crust)
What are the three types of plate boundaries?
- Divergent
- Convergent
- Transform
What is polarity?
-Unlike the geographic North and South, the magnetic North and South shift and reverse over time.
-When both magnetic and geographic norths and souths point in the same direction, they are of normal polarity.
-In opposite directions, they are at reverse polarity.
Explain magnetic stripping and how it occurs.
-Magnetic stripping is a zebra like pattern
-Where strips of normal polarity rocks and reverse polarity rocks alternate on the sea floor
-It is symmetrical on both sides of the mid-ocean ridge.
-The further out it is from the ridge, the older it is.
-It occurs as oceanic plates diverge
-And iron-rich lava erupts from the centre of the ridge
-The lava looses heat and solidifies to form new oceanic crust
-The crust is then pushed away in both directions from the ridge when new lava cools and solidifies.
-When Earth’s polarity reverses, the rocks record the reversals
-Over time, the polarity alternates so the rocks create a strip pattern of different polarity. Reversed and normal.
Example of O-O divergent plate boundary
North American plate and Eurasian plate.
Example of C-C divergent plate boundary.
Nubian plate and Somalian Plate.
Example of O-O convergent plate boundary.
Philippine Plate and Pacific plate.
Example of O-C convergent plate boundary.
Nazca Plate and South American plate
Example of C-C convergent plate boundary.
Eurasian plate and Indo-Australian plate
Example of transform plate boundary.
San Andreas Fault where Pacific plate slides past North American plate.
In C-C convergence, what happens and what is created?
-Folding, uplift, and buckling occurs in the continental plates due to pressure.
-This creates fold range mountains and earthquakes due to the friction from the collision, causing seismic activity.
What happens during O-C convergence, and what is formed?
-Subduction happens and the oceanic plate dewaters due to high heat and pressure.
-The dewatering lowers the temperature of the surrounding mantle material which forms magma that rises through the weak areas/cracks and fissures of the continental plate. This forms volcanoes.
-The subducting plate forms deep sea trench.
-Earthquakes along the subducting Oceanic plate.
What happens and forms at an O-O divergence?
-Decrease in pressure cause mantle below to melt, forming magma.
-Which rises through the cracks and fissures of the crust to the surface of the earth. Fills up with magma —> lava, solidifies and forms new oceanic crust.
-Continues to solidify to form mid oceanic ridge
-volcanic islands+volcanoes
How do earthquakes form?
-The sudden release of energy in lithosphere shakes the ground
-focus is where seismic waves are released (origin of earthquake)
-epicentre where shaking felt most strongly on surface (directly above focus)
What types of seismometers are there?
- Richter Scale (largest wave recorded)
- Moment magnitude scale (total energy released)
Comparison criteria of strata and shield volcanoes.
(In terms of eruptions)
-High/low silica Magma (more viscous/effusive)
-Larger eruption/ more explosive (more/less pressure build up of gases)
-Violent/effusive eruptions
-wide range/small range
Comparison criteria of strata and shield volcanoes.
-Tall
-Steep sides
-narrow summit
-shorter in height
-gentle slopping sides
-broad summit
How are earthquakes distributed?
-majority found at plate boundaries
-largest concentration is at Pacific Ring of Fire
How are volcanoes distributed?
-Generally near convergent and divergent plate boundaries
-convergent plate boundaries: belts of volcanoes along subduction zones in pacific ring of fire.
-not near transform + c-c convergence
-exception away from plate boundaries: Piton de la Fournaise volcano on Reunion island in Indian Ocean.
What are earthquake the hazards?
- Ground shaking
- Soil liquefaction
- Landslides
- Tsunamis
What are the volcanic hazards?
- Tephra
2.Volcanic gases - Lava flows
- Pyroclastic flow
- Lahars
- Volcanic landslides
How does ground shaking affect natural+human systems?
-Destroys ecosystems: •Ruptures oil and chemical factories, polluting land and water.
•Fractures and uproot trees, causing wild spread tree injury and death and damaging wildlife habitats.
-Destroys properties+infrastructure:
•weakens buildings, bridges, roads and railways, causing them to collapse, difficult to save/supply emergency aid.
-Cause injuries+fatalities:
•trapped under collapsed buildings
Examples of ground shaking affecting humans+nature
2010 Haiti earthquake
•surrounding areas around factories polluted
•debris polluted rivers
•more than 250000 houses collapsed due to violent vibrations.
•220000 people killed
How does soil liquefaction affect natural+human systems
Soil liquefaction—> violent ground shaking causes saturated loose soil to lose structure become thick fluid
-Destroys ecosystems:
•Trees on liquefied soil sink, tip over, damage wildlife habitat = loss in forest and biodiversity.
•Liquefied soil enter rivers (pollute) and smother aquatic plants = aquatic species die
-Destroys properties/infrastructure:
•Buildings sink, tip over, takes time and resources to recover + hard to rescue people.
How do tsunamis form?
- Plate slip = undersea earthquake
- Displacement of water
- Large volumes of water lifted, form waves of great wavelengths low height less than 1 metre (bc very shallow)
- When approach coast, more friction and seabed shallower = slow wave down
- Waves get closer increase in height up to 15m at speed 30-50km/h
- (How to tell whether tsunami might occur—> sea will recede from shore as it fills the void from displacement of seabed.
Impacts of tsunamis on natural+human systems
-Destroys ecosystems:
•seawater flood coastal wetlands and forests, damaging habitats
•Large amount of debris carried by waves pollute large areas of land/ocean when water recede (damage ecosystems and kill wildlife)
-Destroys properties/infrastructure:
•Fast moving water+debris can sweep away buildings/ destroy them (take a lot of resources and time to repair)
-Disrupts services:
•tsunami fast water+debris can snap electricity/communication cables
•sweep away roads+railways (hard to rescue people)
Example of impact of tsunami
2011 Tohoku, Japan earthquake:
•Tsunami height 40m
•Destroyed homes, infrastructure
•pollute with debris + seawater
•Coastal city of Sendai lost half its population (+damaged infrastructure)
