TECTONICS EQ1 Flashcards
why are some locations more at risk from tectonic hazards? (39 cards)
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 or the economy.
-Includes earthquakes and volcanic activity.
What is an earthquake?
Sudden violent shaking of the ground is caused by the release of energy in the earth’s crust, typically due to the movement of tectonic plates.
What is a volcanic eruption?
-The release of magma, ash, and gases from a volcano, which is an opening in the Earth’s crust.
-This process can be either effusive (producing lava flows) or explosive (producing pyroclastic flows and ash clouds).
What is a tsunami?
-A long, high sea wave produced by a disturbance, such as a volcanic eruption, submarine earthquake or coastal landslide.
What influences the distribution of earthquakes, tsunami and volcanoes?
-Earthquakes:
This happens in distinct zones at the edges of tectonic plates (plate boundaries). Also occurs in intraplate regions, which may be caused by stress buildup, continental rifting, etc.
-Volcanoes:
Active around plate boundaries. Mostly on the “Pacific Ring of Fire (75%). Found at convergent and divergent boundaries. It can also be a ‘hotspot’ in the middle of plates.
-Tsunamis:
70% in the Pacific Ocean. Caused by tectonic activity. Mostly at convergent boundaries.
What are the three main earthquake belts?
-Pacific belt (ring of fire)
-Alpide belt
-Atlantic mid-ocean ridge
Oceanic crust is…
- made of denser rock types
-created at divergent plate boundaries
-Thinner than continental crust
Continental crust is…
-made of less dense rock types
-created at convergent plate boundaries
-Thicker than oceanic
Earths structure: crust
-Made up of oceanic and continental.
-Continental: thicker (45-50km), less dense (mostly granite)
-Oceanic: thinner (6-10km) and denser (mostly basalt)
Consists of seven major and several minor tectonic plates.
Earths structure: mantle
-between the crust and the core, the widest layer
-Upper crust:
Lithosphere (crust and most solid mantle)- rigid layer above the asthenosphere
. Asthenosphere - semi-molten plastic-type layer which moves under high pressure. -(IMPORTANT) No movement would occur without it
- Lower mantle:
Hotter and denser than the upper mantle. The intense pressure at depth keeps the lower mantle solid
Earths structure: core
-Inner core:
The solid centre, mostly composed of iron
-Outer core:
Semi-molten, mostly liquid iron and nickel
What is a divergent (constructive) plate boundary?
-Plates move apart (diverge)
- Convection currents push the plates apart and cause a gap
Magma rises to fill the gap, and a new crust is created
- frequent low-magnitude earthquakes
-small and effusive eruptions
-basaltic eruptions ( low gas content, low viscosity, high temp)
What is a convergent (destructive) plate boundary?
-The plates move towards each other (converge), resulting in collision and the destruction or deformation of the crust.
-Friction and pressure build up in the Benioff zone, causing earthquakes
-Volcanic eruptions become explosive as the magma rises to the surface.
-Rhyolitic eruptions (high gas content, high viscosity, low temp)
What is a subducting plate boundary?
-Where the oceanic plates subduct beneath the continental plate
- also leads to fold mountains when rocks are pushed upwards by collision
-Oceanic subduction causes friction along the subducting plate.
-This is called the Benioff zone and can cause deep earthquakes far from the plate margin.
What is a conservative plate boundary?
-Where two crustal plates slide past each other, and the movement of the plates is parallel to the plate margin
-Plates can stick, causing a significant build-up of pressure and powerful earthquakes
What is intra-plate/hot-spot volcanism?
-Some earthquakes and volcanic eruptions occur away from the plate boundaries. These are intraplate earthquakes and hot spots.
-Hot spot volcanoes occur over stationary mantle plumes (columns of rising magma) in the asthenosphere. The tectonic plate moves over the plume, forming volcanic island chains (Hawaii). The oldest is the one furthest from the plume.
What are the two theories of plate tectonics?
Alfred Wegener’s theory of continental drift
Harry Hess’ theory of seafloor spreading
Describe Alfred Wegners theory of continental drift
- The continents had once formed a single landmass called Pangaea, before breaking apart and drifting to different locations.
Describe Harry Hess’s theory of seafloor spreading
-Basaltic magma rises at a divergent plate to create new ocean floors at mid-ocean ridges.
-When magma rises at divergent plates, the rock begins to cool, and the minerals align with the magnetic poles of the Earth. We see stripes as the mineral alternatively faces north and south, which could flip every 100,000 years, proving the theory of seafloor spreading.
What is paeleomagnetism?
-Palaeomagnetism refers to the study of Earth’s past magnetic field, recorded in rocks and sediments
Why does the lithosphere move?
-Due to a combination of convection currents in the Earth’s mantle, slab pull, and ridge push
What is slab pull?
-Happens in the presence of subduction
-The weight of the sinking subducting plate causes a pulling action, pulling the rest of the plates down as well.
What is ridge push?
-Occurs at mid-ocean lithospheric ridges where the lithosphere rises and newly formed plates slide sideways, pushing the plate in front of them, triggering ridge push.
Which scale is most commonly used to measure earthquakes?
Moment Magnitude scale
