Tectonic Hazards Flashcards
Describe the makeup of the Earths?
The Earths mantle is semi-molten 5000oc
The centre of the Earth= the core= inner core 5500oc and outer core
Outside this there’s the mantle, the layer within the mantle, but below the lithosphere (crust)= ASENOSPEHRE
What’s the theory of Plate Reactions?
The lithosphere is divided into lots of slabs called tectonic plates
Compare oceanic and continental crust?
OCEANIC- thinner and more dense
- (6-10km)
- Basaltic Rock
- Goes under (subducts) under continental plates
- Younger than continental- 3.0p (density)
CONTINENTAL- thicker and less dense
- (30-70km)
- Granitic Rock
- Doesn’t subduct
- Older than oceanic- 2.6p (density)
What takes place at Constructive margins?
VOLCANOES, EARTHQUAKES, OCEAN RIDGE, RIFT VALLEY
-two plates move apart and “diverge”
-the mantle is under pressure from plates above and when plates pull apart magma rises (less dense than plate above)
When pressure builds a plate can crack causing a fault line and making an EARTHQUAKE
What specific landforms can be found at constructive plates?
OCEAN RIDGE- plates diverge UNDERWATER
eg: Mid Atlantic Ridge- a mostly underwater mountain range
RIFT VALLEY- plates diverge and causes the continental crust between two parallel faults to drop eg: East African Rift Valley
Exam point Answer of what happens at CONSTRUCTIVE margins?
- plates diverge
- convection currents diverge and gap is created between the plates
- magma (less dense) rises up to fill the gaps created
- rift valleys can be created if plates pull apart and the land drops to create a valley eg: East African Rift System
What takes place at Destructive margins?
VOLCANOES, EARTHQUAKES, DEEP SEA TRENCH, ISLAND ARCS, FOLD MOUNTAINS- plates converge
Oceanic- continental= more dense oceanic is forced under continental= deep sea trench at destructive subduction boundaries
Oceanic- oceanic= the more dense of the two is forced under the other, volcanic eruptions that take place underwater create ISLAND ARCS eg: Marina Islands
Continental- continental= FOLD MOUNTAINS- made up of sediments that have accumulated on continental crust
Exam point Answer of what happens at Destructive Plates?
- oceanic plate (denser) subsides beneath continental crust
- crust is DETSTROYED as one plate moves under another at the SUBDUCTION zone
- rocks catch against each other as plates aren’t smooth
- pressure builds until the plates can’t take the stress- they SLIP past each other causing the ground to shake
What takes place at Conservative margins?
ONLY EARTHQUAKES
When two plates are moving past eachother- the two plates get locked together in places and pressure builds up eg: Pacific Plate moving past North American Plate
= San Andreas Fault in California
Exam point Answer of what happens at Conservative Plates?
- Plates slide past each other horizontally
- Crust is neither created or detroyed
- The plates are made of rock that has jagged edges so they snag and PRESSURE AND FRICTION builds up
- The plates SLIP past each other= EARTHQUAKES
When did Plato theorise the earths structure consisted of multiple spheres?
2000 YEARS AGO
What specific shape is the Earth?
A geoid- it bulges at the equator and is flatter at the plates.
What is continental crust also known as?
Sial Crust
What is oceanic crust also known as?
Sima
What does the lithosphere consist of?
The crust and upper mantle. It is the zone that tectonic plates are formed.(Rigid)
What does the asthenosphere consist of?
Lies directly below the Lithosphere and includes the rest of the mantle where rocks are much softer. (Plastic)
What is the Moho discontinuity?
The boundary between the crust and mantle.
Which tectonic theory did Alfred Wegner propose?
A German Meteorologist
Proposed the theory of “continental drift”
What evidence is there of the continental drift theory?
- Coal has been found in Antarctica= unlikely to have formed as needs tropical climates and dense vegetation
- Upper carboniferous glaciation found in the southern hemisphere
What did the CONTINENTAL DRIFT theory evolve into and differences?
PLATE TECTONIC THEORY
-seismometers monitored the ground shaking and found that earthquakes occurred on specific plates than equally over the earth
- states the crust is broken up into 20 sections
- explains why the earth’s crusts are moving
CONTINENTAL DRIFT
- hypothesised all modern day continents had been previously clumped together in a “supercontinent” called PANGEA
- Wegner stated that over millions of the years Pangea had drifted apart
- Reconfiguration= a “Pangea Proximia”
What is intra plate volcanism?
Plate activity AWAY from the plate boundary.
What happens when two continental plates at a destructive margin (convergent) collide?
Creates fold mountains as subduction doesn’t occur, land bulges upwards.
Folding of layers of lithosphere.
eg: Himalayas
What happens when two destructive plates at a destructive margin (convergent) meet?
The faster, more sense plate subducts under the other.
How to hot-spots (intra-plate volcanism) form?
=STATIONARY action away from a plate boundary
Form due to concentrated spots of radioactive decay in the core
Concentrated spots of radioactive decay heat the lower mantle= MAGMA PLUME forms= rises vertically.
Define “magma-plume”?
What do magma plumes cause?
A vertical column of extra-hot magma that rises from the mantle.
They cause intense volcanic activity away from plate margins.
How was Hawaii formed?
-Magma plume forms which cause extreme volcanic activity away from the plate margin
-Volcanoes form above the magma plume
-The magma plume stays stationary over time but the crust moves about it
-Volcanic activity deceases at specific parts of the crust where it moves away
-New volcanoes form above the magma plume/ hotspot
=CHAIN of volcanoes= HAWAII
How was Hawaii formed?
-Magma plume forms which cause extreme volcanic activity away from the plate margin
-Volcanoes form above the magma plume
-The magma plume stays stationary over time but the crust moves about it
-Volcanic activity deceases at specific parts of the crust where it moves away
-New volcanoes form above the magma plume/ hotspot
=CHAIN of volcanoes= HAWAII
What are the two main types of plate movement?
FOLDING-Two plates come together and push against each other
Ripples at the surface form
High points of ripples= anticlines
Low points of ripples= synclines
FAULTING- Usually parallel in a “fault zone”
- DIPSLIPS (vertically up and down)
- STRIKE SLIPS (horizontally left to right)
eg: San Andreas Fault- Pacific and NA plate.
What can marine erosion and subsidence cause to happen to volcanic hotspots?
Marine erosion and subsidence can reduce these hotspot volcanoes to seamounts, which may form coral atolls overtime.
