Tectonics theory Flashcards
Global distribution of earthquakes
95% along plate boundaries
90% pacific ring of fire
Follow the oceanic fracture zone and the continental fracture zone
Global distribution of volcanoes
50 erupt each year
80% of active volcanoes are on destructive plate boundaries
Global tsunami distribution
Earthquake generated
90% occur within the Pacific Basin
most generated at subduction zones
Japan-Taiwan Island arc
Divergent plate boundaries
Commonly found at mid ocean ridges where sea-floor spreading occur
Rift valleys on the continent
New oceanic pate is formed
Low risk shallow focus submarine earthquakes
Low risk shield or rift volcanoes
Drift
Convergent plate boundaries
Potential to create huge mountain ranges or large subduction zones with areas of great friction and ocean trenches
Infrequent high magnitude earthquakes (Japan 2011)
composite volcanoes
Lithosphere is destroyed
connect
Conservative plate boundaries
Relative horizontal movement
Lithosphere is neither created or destroyed
No volcanic activity
Occasionally high magnitude shallow focus earthquakes
San Andreas Fault
Formation of an intra-plate volcano
Mantle plume- high level of heat in the mantle
Magma rises from the asthenosphere to the lithosphere due to density changes.
Plate movement causes the shape to shift into a bulbous head at the top of the conduit.
Magma escapes onto the seafloor by exploiting a weakness or burning through the crust.
Repeats.
Magma cools and hardens forming an active volcano.
Plate movement shifts away from hot spot, unactive chain of islands.
Formation of an earthquake
Caused by sudden movements near the Earths surface along a fault
Plate movement causes a build up of strain and energy.
Pressure exceeds the strength of the fault and he crust fractures.
Sudden release of energy sends seismic waves radiating outwards causing the surface to shake.
Formation of a tsunami.
Seismic energy released during an earthquake causes the seafloor to uplift displacing the above water column.
Gravity drags the water column back down, splits into waves travelling in all directions.
In shallow water friction causes the water to slow down increasing wave height and decreasing wave length.
Vacuum effect draws water out to sea.
Travels up to 600kph for 1 mile inland.
Mantle convection
Heat from the radioactive decay in the core causes density changes in the mantle, magma circulates in cells.
Seafloor spreading
Hot magma rising from the asthenosphere pushes tectonic plates apart at mid ocean ridges, mainly occurs at divergent plate boundaries.
Credited with gap filling
Subduction zone movement
Weight of sinking oceanic plate pulls it into the subduction zone at convergent plate boundaries, may also pull continental plate downwards.
Slab pull
Newly formed oceanic crust at becomes denser and thicker as it cools pulling the plate down into the mantle.
The Benioff zone
An area of seismic activity corresponding with the slab being pulled downwards into the subduction zone.
Cross section of land identifies volcano location and determines the position of the earthquakes hypocentre.
Important at explaining magnitude.
Primary hazards of earthquakes
Seismic waves = higher frequency/amplitude = more dangerous
P waves = vibrations caused by compression, fastest, solids and liquids 8kph least damaging
S waves= perpendicular vibrations, move slowly through solids
l waves= horizontal plane, most damaging focus all energy on ground surface
Secondary hazards of earthquakes
Liquefaction- surface rock become more liquid than solid, causes buildings to collapse and infrastructure to collapse, Japan tilts up to 60 degrees
Landslides/Avalanches - sloped weaken and fall growing in size, Mg 4 required
Aftershocks- readjusting of fault line, New Zealand 2011 aftershock higher magnitude than 2010
Tsunamis - Japan 2011
Tsunami threat
Generally low in height with long wavelength when in deap waters
Shallow water increases wave height and decreases wave length.
Speeds up to 600Kph
Sever cause of coastal flooding
Series of waves generated by seismic energy
Primary hazard of volcanoes
Pyroclastic flow
Lava flows
Tephra
Gas eruptions
What are pyroclastic flows?
Fast moving destructive mix of rock, ash and gases reaching up to 1000 degrees.
Cause most volcanic related deaths.
What are lava flows?
fast flowing lava on the surface up to 15m/s and 1000 degrees
What is tephra?
Volcanic ash fragments and rock ejected from the volcano.
reduce visibility and damage infrastructure travelling thousands of kilometers
What are gas eruptions?
Dissolved gases travel huge distances when erupted from the volcano, CO2 methane etc.
What are lahars?
Secondary hazard of a volcano
Flows of rock, mud and water when heavy rainfall re-mobilises old tephra, speed varies depending on land gradient.
What are Jokulhlaups?
Secondary hazard of a volcano
Type of catastrophic glacial outburst, floods occur suddenly and in large volume when ice dams fail due to heat of the volcano.
Modify landforms, through erosion and deposition.
