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EQ1: Why are some locations more at risk from tectonic hazards? (1.1 The…
EQ1: Why are some locations more at risk from tectonic hazards?
1.1 The global distribution of tectonic hazards can be explained by plate boundary and other tectonic processes.
Describe and explain the global distribution of earthquakes, volcanic eruptions and tsunamis
Earthquakes
are found along all types of plate margins as shown on this map.
Volcanoes
however, only occur at constructive and destructive plate margins. A lot of volcanic activity occurs in the 'ring of fire'. The 'ring of fire' is a group of volcanoes that are located along the plate margin of the Pacific plate.
Describe the distribution of plate boundaries (divergent, convergent and conservative)
Divergent margins
(constructive) are most clearly displayed at ocean ridges.
At these locations there are large numbers of shallow focus and generally low magnitude earthquake events. Most are submarine.
Convergent
These are actively deforming collisions with plate material melting in the mantle, causing frequent earthquakes and volcanic eruptions.
Conservative
(oblique-slip, sliding or transform) margins, where one plate slides against another. Here the relative movement is horizontal and classified as either sinistral (to the left) or dextral (to the right).
Lithosphere is neither created nor subducted, and while conservative plate margins do not result in volcanic activity, they are sites of extensive shallow focus earthquakes, occasionally of considerable magnitude.
Explain cause of intra- plate earthquakes and volcanoes
These
intraplate earthquakes
are caused by stresses within a plate. Since plates move over a spherical surface, zones of weakness are created. Intraplate earthquakes happen along these zones of weakness. The earthquakes may take place along ancient faults or rift zones.
1.2 There are theoretical frameworks that attempt to explain plate movements.
Explain the theory of plate tectonics (internal structure, mantle convection, palaeomagnetism and sea floor spreading, subduction and slab pull)
Internal structure
- The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. Each layer has a unique chemical composition, physical state, and can impact life on Earth's surface.
Mantle convection
s - Mantle convection is the very slow creeping motion of Earth's solid silicate mantle caused by convection currents carrying heat from the interior to the planet's surface.
Palaeomagnetism
- he branch of geophysics concerned with the magnetism in rocks that were induced by the earth's magnetic field at the time of their formation.
Sea floor spreading
- Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
Subduction
- is the process of one plate sinking beneath another at a convergent plate boundary
Slab pull
- Slab pull is that part of the motion of a tectonic plate caused by its subduction.
Explain how the processes operate at different margins (destructive, constructive, collision and transform).
Destructive
- one plate subduct under another illustrate the forces that drive plate tectonics. mantle convections pull oceanic plates apart creating the fracture zone at constructive margins and convections also pull plates towards subduction zones.... Earthquakes at subductin zones occur at a range of focal depths from10km to 400 km, following the line of sunducting plate. this is called the benioff zone, and it can yelid very large earthquakes up to magnitude 9.0. the decending plte begins to melt at depth by a process called partial melting. this generates magma with high gas contet, whcih erpts with explosive force.
Constructive
- mantle convection forces plates apart at constructive plate margins. Tensional forces open cracks and faults between the two plates. These plates create pathways for magma to move towards the surface and erupt, creating new oceanic plate. Eruptions are small and effusive in character, as the erupted basalt lava has a low gas content and high viscosity. earthquakes are shallow, less than 60km deep, and have low magnitudes of under 5.0
Collision
- As the plates collide, the oceanic plate is forced beneath the continental plate. ... If two continental plates collide, neither can sink and so the land buckles upwards to form fold mountains. This is called a collision boundary . Earthquakes can occur at collision boundaries.
Transform
- conservative plate boundaries consist of transform faults. These faults 'join up' sections of constructive plate boundaries they transverse the earths surface in a zig-zag pattern. In some locations long transverse faults act like a boundary in their own right, most famously in California where a fault zone - including san Andreas fault - creates and area of frequent earthquake activity. earthquakes along conservative boundaries often have shallow focal depths, meaning high-magnitude earthquakes can be very destructive. Volcanic activity is absent.
Explain how physical processes can impact upon the: 1) magnitude of volcanic eruptions 2) type of eruption 3) magnitude of earthquakes 4)earthquake focal depth
1.3 Physical processes explain the causes of tectonic hazards.
Explain how P, S and L waves cause crustal fracturing, ground shaking and secondary hazards such as liquefaction and landslides.
P waves are the primary waves and are the fastest but the least destructive
S waves are the secondary waves and arrive next and shake the ground violently causing damage
L waves are love waves and arrive last and only travel across the surface and have a large amplitude and cause significant damage including fracturing the grouds surface
Explain how volcanoes cause lava flows, pyroclastic flows, ash falls, gas eruptions, and secondary hazards such as lahars, jökulhlaup.
Lava flow
- expensive areas of solidified lava which can extend several kilometres from volcanic vents if the lava is basaltic and low viscosity it can flow up to 40kmh
Pyroclastic flow
- dense clouds of hot ash and gas at temperatures of up to 600 degrees Celsius. They can flow down the flanks of the volcanic and devastate large areas.
Ash fall
- ash particles and larger tephra particles can blanket huge areas in ash killing vegetation and collapsing buildings and poisoning water.
Gas eruption -
the eruption of carbon dioxide and sulphur dioxide, which can poison people and animals in extreme cases.
Lahar
- volcanic mudflows which occur when rainfall mobilises volcanic ash. They travel at high speeds down river systems and cause major destruction.
Jokulhaup
- devastating floods cause when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of meltwater. they are common in Iceland.
Explain how tsunamis can be caused by sub-marine earthquakes at subduction zones as a result of sea-bed and water column displacement
Tsunamis can be generated by landslide and even eruptions of volcanic eruptions of volcanic islands. Most are generated by submarine earthquakes at subduction zones.
Generated when submarine earthquakes displace the sea bed vertically as a result of movement along the fault line at a subduction zone
The violent motuon displaces large amounyts of water in the sea which generates a tsunami
Wave height are typically less than 1m. wavelengths are usually more than 100km. speeds are 500-950kmh
