1. TECTONICS EQ1 Flashcards
(25 cards)
What are the 4 main types of plate boundaries and how do they work?
Destructive - oceanic plate is denser and is subducted under the continental plate, result in violent earthquakes
Constructive - earths crust is forced apart, magma rises and solidifies creating new crust and mid ocean ridge
Conservative - 2 plates sliding past each other builds up pressure, causes severe earthquakes
Collision - 2 plates moving together are both made form continental crust, land is pushed upwards to form high fold mountains
What are infra-plate earthquakes?
These are found in the middle of plates and is the result of solid crust cracking as it travels over millions of years possibly resulting in the creation of a new plate boundary, associated with smaller magnitude earthquakes.
What are volcanic hotspots?
Volcanic activity in the middle of plates, an upwelling of magma from the core and at the surface they form volcanic hotspots like the Yellowstone hotspot
Why are there no volcanoes at conservative plate margins?
Due to the crust not being destroyed or created
What is the global distribution of earthquake hazards?
Earthquakes and volcanoes are found it clusters along plate boundaries. Nearly 70% found at the pacific ring of fire and the most powerful are associated with destructing and conservative boundaries.
What 5 factors is plate tectonics driven by?
Mantle convection
Slab pull
Subduction
Seafood spreading
Palaeomagnetism
What is mantle convection theory?
Heat rises from the core and as it rises it cools and creates convection currents that become more denser before sinking back into the mantle
What is slab pull theory?
It is the driving force being movements. As newly formed material at mid ocean ridges cools and becomes denser causing the plates to sink into the mantle.
What is seafloor spreading/palaeomagnetism theory?
As new crust is being formed at mid ocean ridges, the crust pushes the plates apart. Studies show that the magnetic field of the rock that had been created changed over time. Magnetic fields change every 400,000 years and can be measured in rocks.
What is Palaeomagnetism theory?
As new rock is created in the centre of the ocean, older rock is pushed to the edges. Every time new rock is created it has magnetic orientation of the time imprinted in it.
What is Subduction theory?
As new crust is being created at mid ocean ridges it is being destroyed by subduction as the end of the plate sinks beneath the continental plate.
What is the evidence for continental drift?
The plates of the earth are slowly moving over time and the earth was once compromised by a super continent called pangea which split up over time into its now positions. The evidence for this is palaeontology, geology, biology and geography.
Paleontology evidence
Fossils of the same dinosaur have been found in Africa, India, and Antarctica and is unable to swim or fly.
Geography evidence
Many of the continents fit together almost perfectly like pieces of a jigsaw.
What are the 3 types of magma?
Basaltic - basic magma
Andesitic - intermediate
Rhyolitic - acidic magma
What are the characteristics of basaltic magma?
-very hot, iron rich, silica poor
-low gas content, very runny lava
-erupt almost continuously
-not very explosive
What are the characteristics of andesitic magma?
-hot, iron poor, silica rich
-sticky, decades or centuries between eruptions
-can be very explosive
What are the characteristics of rhyolitic magma?
-cooler lava, iron poor, silica very rich
-very high gas content (very combustible)
-they erupt rarely, can be devastating
What determines eruption type?
-The crystal, gas content and temperature
-crystals make it more viscous as it cools
-therefore gases build up as they cant escape
-high-temperature magma erupts effusively, whilst low-temperature are more likely to erupt explosively.
What are the primary hazards and their examples?
- lava flows, Hawaii
- pyroclastic flows, Montserrat
- ash fall, Eyjafjallajokull
- gas eruptions - Mnt St. Helens
What are the secondary hazards and their examples?
- lahars, Pinatubo
- jokulhlaup, Eyjafjallajokull
What is the focus and the epicentre?
The focus is the point on the fault where the rupture begins.
The epicentre is the point on the earths surface directly above the focus.
Anatomy of Earthquakes - What are primary waves?
They arrive first, fastest and move through solid rock and fluids.
They push and pull in the direction of travel.
Anatomy of Earthquakes - What are secondary waves?
These are slower than P waves and only move through solid rock.
They have an up and down movement.
