Tectonics EQ1 Flashcards
Where do most earthquakes occur?
At plate boundaries
Intraplate regions due to stress build up
What are the three belts of tectonic activity called?
Pacific belt
Alpide belt
Atlantic Ocean ridge
Where do tsunamis commonly occur?
70% in Pacific Ocean
Mainly due to activity at convergent boundaries
Where are most volcanoes found?
At or near plate boundaries- convergent/ divergent
Hot spots- Hawaii
75% ring of fire
What are intraplate volcanoes?
Volcanic activity that is found in the middle of oceanic and continental plates
Eg Hawaii
How do intraplate volacanoes occur?
Oceanic- magma melts through surface of outer core
Continental- stretched places for magma from hot spots/mantle plumes to break through
What are mantle plumes?
Magma rises from outer core
Forms hot spots which break through crust
They erupt causing volcanic islands
Tend to erupt a lot causing basaltic volcanoes
What are basaltic volcanoes?
Volcanoes with persistent periods of activity
What are the three types of plate?
Divergent
Conservative
Convergent
How do divergent plates move?
Away from each other
What forms at divergent plate boundaries?
Effusive volcanic eruptions: basaltic volcanoes
Rift valleys
Sea floor spreading
Low gas content, high temp eruptions
What type of earthquakes at divergent plates?
Weak and common earthquakes
How do conservative plates move?
Past each other
Up and down arrows
What type of earthquakes are found at conservative plates?
High magnitude, frequency
Powerful
What causes earthquakes at conservative plates?
Plates stick together causing a build up of pressure and stress
What direction do convergent plates move?
Move towards each other
What happened at continental and continental plate boundary?
Fold mountains as plates pushed up as pushed together
What happens at continental and oceanic convergent plate boundary?
Explosive eruptions due to rhyolite lava oceanic plate subducts, melts in the mantle causes ocean trenches
Occasionally forms fold mph rains where rocks are warped and pushed upwards
What happens at oceanic and oceanic convergent plate boundary?
Explosive erruprions due to rhyolite lava, ocean trenches, island arcs
Highest magnitude
Plate can subduct
What causes intraplate earthquakes?
Isn’t known fully, may be pre existing weaknesses in plate which reactivates forming seismic waves
What are the 4 causes of tsunamis?
landslides
underwater eruption/earthquake
seismic activity
tectonic plate movement
What are the 4 steps to formation of a tsunami?
- Submarine earthquake or volcano occurs, causes vertical water column displacement
- A wave travels in all directions
- As the wave moves to shallower water, it slows down and gains height
4.This can travel great distances across land
What is rhyolite lava?
Lava that has a high gas content, high viscosity and low temperature
What are primary hazards of volcanoes?
- lava flows
- pyrolclastic flows
- ash falls
- gas eruption
What are secondary hazards of volcanoes?
- Wild fires
- lahars
- jokulhlaup
What are pyroclastic flows?
Heavier air flows down sides of volcanoes reaching high speed and temp
Considered most dangerous of all volcanic hazards
What is lava flows?
Deaths due to from causes such as explosions of the lava meeting water or asphyxiation due to toxic gas released
What is ash flows?
Ash from eruption that settles on surrounding areas
What are gas eruptions?
Eruption of carbon dioxide and sulphur dioxide that can poison people
What are wild fires?
Kills the environment and spreads quickly
What are lahars?
Mixture of water and volcanic rock fragments which flow quickly down volcanoes
When significant rainfall coincides with eruption
What are jokulhaups?
Glacial outburst floods caused by volcanic eruptions melting snow and ice from glaciers
What is balsaltic magma?
Magma that has a low gas content, a low viscosity and a high temperature
What is a tectonic hazard?
Threats caused by the movement of tectonic plates that have potential to cause damage to life, property, environment, human activity and the economy
What is liquefaction?
Violent shaking causes surface rocks to lose strength and become more liquid then solid
Cannot support anything, causing things to sink
What is the structure of the earth?
Inner core: solid center
Outer core: liquid outer layer creating magnetic field
Mantel: solid layer between core + lithosphere
Asthenosphere: partially melted layer allowing plates to move
Lithosphere: crust + upper mantle fused together
What are the theory of plate tectonics?
Wegner: Pangea l- continents fit together like puzzle forming 1 landmass= 1912
Hess: sea floor spreading
What is mantle convection
Magma heats in centre of earth, rises to surface, moves and cools, sinks to core again, no longer believed to be main cause
What is slab pull?
As subduction occurs crust cools and becomes heavy and sinks causing major pulling action causing rest of plate to be pulled
What is seafloor spreading?
Hot magma pushes through and cools causing new oceanic crust= sea floor spreading
What is ridge push?
Lithosphere at divergent plates is hot and less dense causing it to rise and form oceanic ridges
Formed plates push sideways off high areas pushing plate in front resulting in ridge push
What is the Benioff zone?
Zine if seismicity
What is the seismicity of each plate boundary?
Convergent - highest magnitude, frequent
Conservative - high magnitude, frequent
Divergent - high magnitude, frequent
What are P waves?
Primary waves
Arrive first, fastest and moves through solids + liquids
Only damaging in powerful earthquakes
What are S waves?
Secondary waves
Slower then p waves
Only travel through solids
More damaging then p waves
What are L waves?
Love waves
Travel on surface of crust
Slowest
Most damaging and powerful
What is water column displacement?
Crust pushes up and pushes water up causing displacement causing tsunamis
What is sea bed displacement?
Movement of sea bed upwards or downwards causing water to displace causing tsunamis
