Hazards 1- Geophysical systems Flashcards
Explain continental drift
-The Earth’s crust is made of a number of large and smaller plates.
-These plates are in constant motion, a process called continental drift.
-The plates move at very slow speeds (2-5cm a yr).
-Over millions of years the Earth’s continents come together & separate.
-There are 3 key factors that drive plate movement.
What are the three key factors that drive plate movement?
-Internal heating and convection currents
-Subduction and rifting at plate margins
-Mantle plumes and hot spots
What is the inner core of the Earth made of?
Iron and nickel
What is the temperature in the inner core?
It ranges from 5,000-7,000 °C
How has the heat from the inner core been generated?
-The heat from the inner core has been generated from the great frictional forced that occurred through the Earth’s formation, as well as through radio-active decay of elements.
-It generates 44 trillion watts of heat which flows away from the core to the mantle.
Explain convection currents
-In the mantle is behaves like a viscous liquid ( it has phases of liquid & solid consistency under pressure).
-When the convection cells make contact with the base of the crust, they cause friction & drag the crust along in the general direction of the convection.
Diagram of internal heating and convection currents
Explain ridge push
-At rift zones ( constructive/divergent boundaries) the crust is moving apart under tensional stresses.
-This reduces pressure on the asthenosphere ( lower part of mantle), allowing magma to rise into the lithosphere ( crust & upper mantle- tectonic plates) creating new oceanic crust.
-As it moves away from the ridge it cools, solidifies and sinks creating a slope, enabling further movement.
Explain subduction and slab pull
-At destructive plate boundaries, denser oceanic plate is subducted under the less dense continental plate e.g. at deep ocean trenches, volcanic activity 100km from the plate boundary on the continental side, and earthquake focal points as deep as 700km along the Benioff zone.
-As a slab of oceanic plate descends, it pulls ( perhaps with some suction) the rest of the plate with it.
Diagram of ridge push and slab pull
How many massive mantle plumes are there in the Earth’s mantle?
Two
What are the two massive mantle plumes in the Earth’s mantle layer
One is centred under the Pacific plate and the other under the African plate.
Explain how hot spots are created
-Molten viscous silicate material rises from the outer core/mantle boundary to about 700km beneath the lithosphere ( crust).
-From these mantle plumes, small hot spots are created where magma rises through the asthenosphere and sometimes breaks through the crust.
-Isolated hotspots occur where there is an upselling of molten material directly from the outer core/mantle boundary to the surface e.g. Hawaiian islands.
What is a flood basalt?
The result of a giant volcanic eruption or a series of eruptions which covers large stretches of land or ocean floor with basalt lava.
Diagram of a hot spot and flood basalts
Explain what evidence of mantle dynamics has revealed about how plates move
-Evidence of mantle dynamics from sources such as seismic tomography have allowed us to develop our understanding of the mechanisms that move plates.
-It seems, rather than being carried passively like rafts on huge convections cells in the mantle, that the plates themselves appear to be the main cause of the convection system in our plantet.
-Mantle convection not only includes the plates, but is primarily driven by them.
Explain how plates move by ridge push and slab pull
-The loss of heat from the lithosphere over time causes it to eventually become cold and dense enough to have negative bouyancy.
-This allows it to sink into the warmer and more ductile asthenosphere.
-This drags the surface plates by slab pull, which appears to be the main force responsible for plate movement.
-This, in turn, creates tension forces elsewhere on the plate (e.g. the Mid-Atlantic Ridge), thinning it and causing passive convection upwelling of the hotter mantle rock in response to the movement of the plates above (the convection seems to be an induced upwelling).
-This forms the ridge that slides away laterally as it cools, pushing the plates apart by ridge push and contributing to the process of slab pull to move the plates.
-This solid but ductile rock of the atmosphere does flow, but the movements there seem to be mostly induced by the movements of the plates (like how a paddle pushes water around as it moves through the water).
Diagram explaining slab pull and ridge push
Diagram explaining mantle dynamics
Diagram of how islands move
How many different types of plate margins are there?
Four
What are the four types of plate margins?
-Constructive
-Conservative
-Destructive
-Collision
Explain how constructive (divergent) plate margin works
-At adivergent plate boundary- also known as a constructive plate boundary, the plates move apart from one another.
-When this happens, the magma from the mantle rises up to make (or construct) new crust.
-The movement of the plates over the mantle can cause earthquakes.
-Rising magma can also create shield volcanoes.
-Landforms at a divergent plate boundary includeocean ridges,rift valleys, and shield volcanoes.
What landforms form at a constructive plate boundary?
-Ocean ridges
-Rift valleys
-Shield volcanoes
Give examples of constructive plate margins
-Ocean ridges, eg the Mid-Atlantic ridge (where the Eurasian plate and the North Atlantic plate are movingapartfrom each other under the Atlantic Ocean)
-Rift valleyseg the East African Rift Valley
Explain how conservative boundaries work
-Atconservative plate margins,fault lineswill be formed.
-These are plate boundaries where two plates are either slipping past each other in opposite directions or at different rates in the same direction.
-The plates do not move past each other smoothly.
-There will often be a build-up of friction or energy that is ultimately released as an earthquake.
Give an example of a conservative plate margin
TheSan Andreas Fault,where the Pacific and the North American plates are sliding past each other.
Explain how destructive plate margins work
-As the plates collide, the oceanic plate is forced beneath the continental plate.
-This is known assubductionand results in the formation of anocean trench.
-This happens because the oceanic plate is denser (heavier) than the continental plate.
-When the plate sinks into the mantle it melts to form magma.
-The pressure of the magma builds up beneath the Earth’s surface.
-The magma escapes through weaknesses in the rock and rises up through acomposite volcano, also known as astratovolcano.
-The volcanic eruptions are often violent, with lots of steam, gas, and ash.
Explain how collision boundaries work
-Collision zones form when two continental plates move towards each other and collide.
-The land between the plates is forced upwards to form fold mountains, eg The Alps and Himalayas.
Give examples of collision boundaries
The Alps and Himalayas
Diagram of a constructive plate margin
Diagram of a conservative plate margin
Diagram of the San Andreas Fault
Diagram of a destructive plate margin
Diagram of a collision plate margin
What are the different types of volcanoes?
-Composite
-Shield
-Cinder cone
Where do volcanoes form?
-Destructive and constructive plate margins
-Above hot spots
Where are composite volcanoes found
Ondestructive plate margins, where the oceanic crust sinks beneath the continental crust.
Explain how composite volcanoes form
-At destructive plate margins, the oceanic crust sinks beneath the continental crust.
-Magma rising from the deep boundary has plenty of time to pick up silica-rich components.
What are the characteristics of composite volcanoes?
-Acidic lava, which is very viscous (sticky).
-Steep sides as the lava doesn’t flow very far before it solidifies.
-Alternate layers of ash and lava. For this reason, they’re also known asstratovolcanoes. Strato means layers.
-Violent eruptions.
-Longer periods between eruptions.
Diagram of a composite volcano
Where are shield volcanoes found?
-Onconstructive plate margins, where two plates move away from one another.
-They also often form in oceans, where the oceanic crust is thinner.
Explain how shield volcanoes form
-Onconstructive plate margins, two plates move away from one another.
-They also often form in oceans, where the oceanic crust is thinner.
-The magma thus doesn’t have far to travel and has less time to change its composition to become silica-rich.
What are the characteristics of shield volcanoes?
-Basic lava, which is non-acidic and very runny
-Gentle sides as the lava flows for long distances before it solidifies
-No layers, as the volcano just consists of lava
-Less violent eruptions
-Shorter periods between eruptions
Diagram of a shield volcano
What type of volcano is Mauna Loa (Hawaii) and where was it formed?
It is a shield volcano, but was formed over ahot spot, rather than at a constructive plate margin, like other volcanoes.
Explain how cinder cone volcanoes form
-They form when runny, low silica magma contains a lot of dissolved gas.
-The gassy eruptions explode and sputter like soda spraying from a can.
-They issue loose volcanic fragments called cinders which settle and pile in conical shapes.
Diagram of a cinder cone volcano
Diagram of the three types of volcanoes
What are the different types of volcanic eruptions?
-Effusive
-Explosive
Table comparing the type of plate margin (constructive vs. destructive) to the nature of the activity
Diagram of the different types of seismic waves (seismogram)
Diagram of the types of faulting
Diagram of soil liquefaction
Diagram of a tsunami in the deep ocean and approaching shore
Diagram of how mass movement happens
Diagram of dry, moist, and saturated soil
Annotated pictures of the effect of human activity on shear strength
Table showing what factors contribute to shear strength
Triangle diagram of the types of mass movement (check(
Diagram showing how mass movements differ with wetness and speed
Diagram showing falls and topples in mass movement
Diagram showing flows in mass movement
Diagram showing slides in mass movement
