Tectonic hazards Flashcards
Alfred Werner’s tectonic theory
- 1912
- proposed continental drift from pangea
Evidence : - fossils from some species found of different continents today
- rock types in different continents
Hess’ theory
- 1962
- proposed the sea floor was created at mid-ocean ridges by convention of the mantle.
- youngest rocks in centre, oldest at the edges
Vine and Matthew’s
- 1963
- provided evidence for Hess’ hypothesis that sea floor was spreading
explain please Ridge Push
- As magma rises between plates it heats the edge of the plates up causing them to expand and rise creating a slope.
- Gravity causes the plates to slide away from the ridge, as older lithosphere is denser compared to the newly formed as more material added over time
Explain slab-pull
- At a subduction boundary the denser heavier plate subduction as its older (more material)
- Gravity then pulls the rest of the plate along with it causing the whole plate to move towards the boundary
Explain convection currents
- Rock heats up at the core causing it to melt and rise.
- At the crust it moves horizontally and cools slightly.
- The magma then sinks back down to the core where it heats up again.
- Process repeats and plate is continuously “dragged” along
Explain a Conservative (Ocean-Ocean) plate margin
- The 2 plates are moving apart
- Magma rises between the gap forming new elevated land (ocean ridge)
- Magma filling the gaps is called sea floor spreading
Landforms at constructive (ocean-ocean) plate margin
- Underwater volcanoes ( low explosivity)
- Ocean ridge
- Earthquakes occur along fractures as plates move (small + frequent)
Explain constructive (continental-continental) plate margin
- 2 plates move apart
- Land in the middle partially collapse (creates rift valley)
- Eventually gap fills with water and separates completely from mainland
- Lifted areas of land are Horsts
- Valley itself is a Grabden
Landforms at constructive (continental-continental) plate margin
- Rift valley (where land collapses)
- Horsts (Raised edges of land)
-Grabden (valley itself)
-Volcanoes (where magma rises)
-Earthquakes along fractures (small and frequent)
Explain a conservative plate margin
- Same for either crust the plates are
- Parallel plates move in opposite directions/different speeds
-No plates destroyed so no landform
-Force of friction resists plate movement, as pressure builds an earthquake is released
-With an oceanic crust a tsunami
Explain a destructive (continental-oceanic) plate margin
-2 plates move towards each other
-Denser oceanic plate subducts
-This brings water-bearing sediments into mantle so lowers m.p of the plate so it melts into magma
- Magma rises through continental crust to create a chain of volcanoes
Landforms made at a destructive continental-oceanic plate margin
- Ocean trench (when oceanic plate subducts)
-Chain of volcanoes (from along continental plate above subduction zone) - Powerful earthquakes when plate subducts
Explain destructive (oceanic-oceanic) plate margin
- The heavier/denser plate subducts
-Water bearing sediments pushed into the mantle lower m.p of plate so turns into magma
-This then rises to form a chain of volcanoes called an island arc
Landforms of destructive oceanic-oceanic plate margin
-Ocean trench (when plate subducts)
-Island arc (chain of volcanoes) explosive
-Powerful earthquakes at interface between plates
Explain a collision plate margin (continental-continental)
-At this convergent plate boundary 2 continental plates collide
-Bith have a lower density than the mantle preventing subduction
-Creates a “pile up” of continental crust on top of lithosphere creating fold mountains
Landforms of collision plate boundary (continental-continental)
-Fold mountains
-Earthquakes (as plates move)
Define a Hotspot
Areas of high volcanic activity far away from plate boundaries
How do Hotspots form ?
-Area of the mantle is hotter than that around it. (greater concentration of radioactive elements so it’s hotter)
-Makes magma less dense so a plume of magma rises
-This will pierce the crust creating volcanic activity
How does a Hotspot form a chain of volcanic islands ?
-Magma plume stays stationary as the crust moves above it
-As tectonic plate moves, magma finds weakness and pushes its way though
-As it breaks through the crust a volcano forms
-Older volcanos sit in the sea and are eroded so they’re smaller than new
