Topic1 - Tectonic Processes And Hazards EQ1 Flashcards
What is a tectonic hazard?
threats caused by the movement of tectonic plates that have the potential to cause damage to life, property, the environment, human activity and/or the economy
- include earthquakes and volcanic eruptions, aswell as secondary hazards like tsunamis
- classed as seismic or volcanic
Outline the distribution of earthquakes around the world?
- main earthquake zones are found (often in clusters) alongside plate boundaries OFZ and CFZ zones
- about 70% are in the ‘Ring of fire’
- the most powerful are at convergent or conservative boundaries
- rare intra-plate earthquakes can happen near the middle of plates - associated with ancient faults
Outline the distribution of earthquakes with focus on oceanic fracture zones (OFZ)?
A belt of activity through the ocean along the mid-ocean ridges, coming ashore in Africa, the Red Sea, the Dead Sea rift and California
Outline the distribution of earthquakes with focus on continental fracture zones (CFZ)?
A belt following the mountain ranges from Spain, via the alps, to the Middle East, the Himalayas to the East Indies and then around the pacific
Outline the distribution of volcanos around the world?
- most active volcanoes occur on or near to plate boundaries
- about 75% occur around the ‘Ring of Fire’ surrounding the Pacific Ocean
- Volcanoes occur at convergent and divergent plate boundaries - also found in the middle of plates at hotspots in the middle of plates like Hawaii
Outline all seven of the major plates which form the bulk of the continents and the oceans?
- North American plate
- Eurasian plate
- Pacific plate
- South American plate.
- African plate
- Indo-Australian plate
- Antarctic plate
Outline the distribution of tsunamis around the world?
- Over 70% of tsunamis occur around the Pacific Ocean
- 15% Mediterranean Sea, 9% Caribbean Sea and Atlantic Ocean
- caused by tectonic activity most occur due to activity at convergent boundaries
What are the three categories of convergent boundaries (plates moving towards each other)?
- Oceanic - continental
- Oceanic - oceanic
- Continental - continental (also known as a collision boundary)
forms mountains and volcanoes
Explain how volcanos happen at intra plate locations - explain mantle plumes and hotspots?
Mantle plume - especially hot areas of the mantle that move upwards underneath the crust and push it up - can cause weak points in the crust which become hot spots
Hot spots - magma from mantle breaks through crust - 2 types (one associated with individual upwelling from near the core mantle boundary - second from top of large mantle plumes)
outline the 2 plate boundaries associated with formation of volcanoes?
- Plates rip apart at a divergent plate boundary, causing volcanic activity and shallow earthquakes
- convergent plate boundary, one plate “subducts” beneath the other, resulting in a variety of earthquakes and a line of volcanoes on the overriding plate
also caused by hotspots
Outline the distribution of earthquakes with focus on continental interiors?
Scattered earthquakes in continental interiors - can also occur along old fault lines
Outline the 4 main parts of the earths structure?
- crust (oceanic and continental)
- mantle
- outer core
- inner core
Outline and explain the characteristics of the earths crust?
- surface temperature to about 400 degrees
- less dense
- composed mainly of granite (continental) and basalt (oceanic)
- solid physical state
- 7km to 70km thick
- surface and body waves able to pass through
Outline and explain the characteristics of the earths mantle?
- temperature around 870 degrees
- less dense to medium density
- composed of magnesium, aluminum, silicon, and oxygen silicates
- phases of liquid and solid state
- body waves pass through at varying rates due to differences in density
- 700 to 2890 km deep
Outline and explain the characteristics of the earths outer core?
- temperature from 4440 to 6100 degrees
- high density
- made up of mainly sulphur and iron
- liquid state - generates magnetic field
- only P waves able to pass through
- 2890 to 5150 km deep
Outline and explain the characteristics of the earths inner core?
- temperature of 7000 degrees - radioactive decay
- very dense
- made up of nickel and iron
- solid state
- only P waves reach inert core and pass through
- 5150 km deep to centre
outline the general idea of continental drift as a hypothesis for plate movement?
Developed by Alfred Wegener based on numerous evidence for example - jigsaw fit, biological evidence, coal deposits and glacial evidence
- idea of a single continent (Pangea) - earths internal radioactive heat was driving force of mantle convection that moves tectonic plates
Outline and explain evidence support for continental drift?
- jigsaw fit - all continent fit together perfectly
- biological evidence - ancient fossils of same species found in different parts of the world
- geological evidence - identical geology found in different parts of the world (mountains in American geologically related to mountains in Scotland)
- glacial evidence - identical glacial till in Antartica, Africa and S America - not possible unless close together
outline the general idea of sea floor spreading as a hypothesis for plate movement?
Magma rising from mantle pushing oceanic crust inside and then coming into contact with water - forms further oceanic crust, oceanic crust pushed way comes into contact with continental crust
Oceanic crust forced under continental back into the mantle
Outline and explain evidence support for sea floor spreading?
Compelling evidence came from the Atlantic ocean sea bed which was spreading outwards from the centre at approx 5 cm a year
- idea that ocean trenches were locations were the ocean floor was destroyed and recycled (mid-ocean ridges were where oceans grew from their centre due to molten material from earths mantle oozing up)
outline the general idea of paleomagnetism as a hypothesis for plate movement?
- earths magnetic field changes every 400,000 years, switching polarity - paleomagnetism study of this
- geologists hypothesised a theory that earths lava changes orientation when polarity switches - when material from mantle rises up through mid ocean ridges and cools it preserves a record of polarity, they noticed symmetrical pattern of magnetic stripes on either sides of the mid ocean ridges, which were same age and similar distance away from ridge on each side - conforms Atlantic floor was created at the mid ocean ridges
Outline and explain evidence support for paleomagnetism?
Geologists notices that on either side of the mid ocean ridges a symmetrical pattern of magnetic stripes - once dating the basalt stripes on the ocean floor, they found the same age at similar distances from each ridge (progressively older the further you go from the ridge)
- shows the Atlantic sea floor was created at mid-Atlantic ridges and then moved sideways
outline the general idea of convection currents as a hypothesis for plate movement?
Holmes’s proposed that the mantle is heated from hotspots in the earths core (created by intense radioactive decay in the core) heat creates convection cells in mantle and causes it to rise and cool, becoming more dense and sinking before repeating the cycle
- plates move slowly due to a frictional drag on the earths lithosphere
Explain reasons for plate movement regarding convection currents?
- convection currents push force created at mid ocean ridges
- slab pull describes how oceanic crust at destructive boundaries become dense and thicker as it cools - causes crust to sink into mantle (pulls plate further down)
- small suction force when plate subducts
Outline the process of sea floor spreading?
1) upwelling convection in mantle causes oceanic crust to form a ridge
2) lateral tension develops causing rift daunting and downward, movements of the central block magma intrudes along faults giving surface lava
3) lateral movements continues with further intrusions parallel to original rift faults
4) main rifting sequence is repeated periodically as upwelling continues
Outline the 3 types of plate boundaries?
- conservative/transform
- constructive/divergent (continental/continental and oceanic/oceanic)
- destructive/convergent (continental/continental, oceanic/oceanic and oceanic/continental)
Outline what happens at a divergent/constructive plate boundary?
Earths lithosphere on 2 different plates move away from each other due to convection currents forming a gap - magma gently rises to surface to fill the gap and create new land (Low volcanoes formed)
- often found in the sea - enough lava eruption can lead to formation of island