Tectonics Flashcards
(127 cards)
What are the 3 tectonic hazards and explain:
- Volcano - a landform that develops around a weakness in earths crust from which molten magma, disrupted from pre-existing volcanic rock, and gases are ejected.
- earthquake - shockwaves created by the release of tension at a focal point
- tsunami - a sequence of huge waves created by a large displacement of seawater, usually by undersea earthquake.
What are 2 ways of classifying tectonic hazards and give an example of each
- primary - eg. earthquakes and volcanos
-secondary - eg. tsunamis (happen as result of primary hazard)
Definition of natural hazard:
- a naturally occurring process or event that has the potential to affect people.
Definition of a natural disaster:
a major but natural hazard that causes significant socioeconomic and environmental damage.
Definition of vulnerability:
the ability to anticipate, cope with, resist and recover from a natural hazard.
What model shows when a natural hazard becomes a disaster? (17/1/25)
Deggs model
What are tectonic plates?
- large irregularly shaped slabs of rock that vary in size and move slowly.
What is the lithosphere?
Earth’s surface layer, made up of the crust and upper mantle, broken into sections with average depth of 100km.
What is the asthenosphere?
The liquid part of mantle that allows some movement of mantle.
What are the 4 types of plate movements?
- convection
- slab pull
- ridge pull
- subduction
Explain convection:
Convection in the mantle was thought to cause plate movement, but is now less accepted. heat from the decay of radioactive elements in the core heats the lower mantle - creating convection currents. These hot magma (molten rock) currents are thought to circulate in the asthensophere, causing plates to move.
Explain slab pull:
slab pull is seen as a driving force for plate movement. Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools. This causes it to sink into the mantle under its own weight - pulling the rest of the plate with it.
Explain ridge push:
As the lithosphere which is formed as divergent plate margins is hotter and less dense than the surrounding area, it rises to form oceanic ridges. These ridges then slide sideways away from these high areas, pushing the plate in front of them. This results in a ridge push mechanism. This movement is enhanced by slab pull.
Explain subduction:
As crust is created in one place, its destroyed in another- by subduction. As oceanic plates (or oceanic plate and continental plate) meet, one slides under the other into the mantle - where it melts in a subduction zone. Slab pulls is the other driving force, pulling other slabs under gravity to the subduction zone.
Look at page 7 of textbook figure 2 to see the mechanisms of crustal movement - ridge push and slab pull
What is a plate boundary?
when two tectonic plates meet.
What are plate margins?
The areas adjacent to plate boundaries and areas either side of the boundary that may be affected by movement.
What are the 3 types of boundaries and explain:
- convergent - where two plates collide also known as destructive margins
- divergent - where two plates move apart, also known as constructive margins
- conservative - where two plates slide past each other, also known as transform margins
What are the 3 types of destructive plates margins and explain:
- Continental-oceanic - Oceanic plate is denser than continental so as they collide oceanic plate slides beneath continental into mantle and melts. Deep ocean trenches occur when oceanic plates start to sink under continental. This subduction leads to formation of fold mountains (as two plates collide, continental plate is folded and pushed up, forming fold mountains. Since plates are constantly moving, fold mountains continue to grow. Friction between colliding plates (and resulting subduction) causes intermediate and deep earthquakes in area called Benioff zone. Volcanic eruptions are generated as magma created by melting oceanic plate pushes up through faults in the continental crust to the surface - causing explosive eruptions. Destructive plate margins are the most seismically active areas of hazards.
- Oceanic - Oceanic - When two oceanic pates collide, the denser or faster is subducted beneath the other. Deep ocean trenches form, and subducted plate melts - creating magma, which rises from Benioff zone to form underwater volcanoes. These can rise above sea level to form seperate island volcanoes, usually found in island arcs. Subduction also produces shallow-to deep-focus powerful earthquakes. The 2004 Indian Ocean tsunami was caused by earthquake where two oceanic plates collided.
- Continental - continental - When two continental plates meet, a collision margin occurs. As both plates have similar density, neither is actually subducted. Instead, they collide and sediments are crumbled and forced up to form fold mountains. Some subduction can occur when compressed denser sediments result in plate subduction. Any earthquakes are likely to have shallow focus - increasing severity.
What two things do constructive plate margins form and explain:
- as constructive plate margins, two plates move apart, which leads to the formation of new crust. In oceans, this forms mid-ocean ridges and on continents it forms rift valleys.
- Mid-ocean ridges - Breaks called transform faults cut across these ridges as they spread at different rates. Shallow focus earthquakes occur, but pose little risk because shocks are minor and occur underwater. Regular eruptions create submarine volcanoes, some of which grow above sea level to create islands.
- Rift valleys - When plates move apart on continents, the crust breaks into sets of parallel cracks (faults). The land between these faults collapses, forming steep sided rift valleys.
Explain what happens at a conservative plate margin:
- along some boundaries, two plates slide past each other, forming a conservative plate margin. This results in a major break in the crust as they move. This break is called a fault and on a large scale is known as a transform fault, which affects wider area. Although no crust is made/destroyed this type of margin is tectonically very active and is associated with powerful earthquakes. The plates sometimes stick as they move, causing stress and pressure to build up which is released as a strong shallow-focus earthquake.
Where are most volcanoes and earthquakes located?
- along plate margins
If a volcano/earthquake doesn’t form along a plate margin where would it form?
Intra-plate earthquakes- occur rarely in the middle of plates, far from plate margins. A series of violent earthquakes (magnitude 7.4-8.6) occured in the New Madrid seismic zone in Missouri, USA during 1811-12.
When do earthquakes become and hazard?
when people are involved as these events can cause mass death and destruction.