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tectonic processes and hazards - Coggle Diagram
tectonic processes and hazards
1.1.1 the global distribution of tectonic hazards
the global distribution of tectonic hazards can be explained by plate boundary and other tectonic processes. all tectonic hazards are caused by radioactive decay in the earths core and mantle generates huge amounts of heat which flow towards earths surface creating convection currents.
earthquake distribution - 95% occur close to a plate boundary
many occur around the ring of fire surrounding the Pacific Ocean
the most powerful earthquakes are usually associated with convergent or conservative plate boudries
intra plate linked with hot spots or old fault lines
volcanoes distribution - most occur near plate boundaries
75% occur around the ring of fire
occur at convergent and divergent
hot spots such as Hawaii in the central pacific
tsunami distribution - over 70% occur around Pacific Ocean
15% Mediterranean Sea 9% Caribbean Sea and Atlantic Ocean 6% Indian Ocean
caused by tectonic activity
most occur due to activity at convergent boundaries
the earths lithosphere is split into 7 major and 7 minor tectonic plates
oceanic
thinner but denser
continental
thicker but more buoyant
two main types of plate boundries
convergent
plates moving together
oceanic - oceanic
oceanic - continental
continental - continental
transform
plates moving past each other
divergent
plates moving apart
intra plate
some earthquakes and volcanic eruption occur away from plate boundaries - intraplate earthquakes and hot spots
intra plate earthquakes
occur anywhere
thought to be caused by tectonic stresses reactivating ancient fault lines
the plates are moving over a spherical surface and this causes zones of weakness
hotspot volcanoes
occur over stationary magma plumes ( collums or rising magma) in the asthenosphere
the tectonic plate moves over the plume leading to the formation of a chain of volcanic islands ( Hawaii)
the oldest island is the one furthest away from the plume
1.1.2. the theory of plate tectonics
plate boundaries
collision / convergent
plates are moving towards eachother
both plates have the same density and are less dense the aesthenosphere beneath them
instead of being subjected they collide and sediments between them are forced up and crumpled to form high fold mountains
this creates collision fold mountains
volcanoes - no as no subduction so no magma is created
earthquakes- are likely to have shallow focus increasing their severity
constructive / divergent
conservative
destructive / convergent
plates are moving towards each other
3 types
oceanic meets continental - oceanic is denser so slides under into the mantle and melts . deep ocean trenches mark start sinks - subduction leads to fold mountains - continental plate is folded and slowly pushed up
earthquakes - the friction between the two plates colliding causes intermediate and deep earthquakes in the benoff zone
volcanoes - volcanic eruptions are generated as magma created by the melting ocean plate pushes up through cracks in the continental crust to reach the surface
destructive most seimically active areas of hazard
mantle convection
the heat from radioactive decay in the core moves upwards into the mantle
it creates convection currents with such up into the spreading mid ocean ridges forcing them further apart called ridge push
subduction and slab pull
convection currents in the mantle drag the overlying lithosphere towards eachother
a subduction zone is formed when two plates meet
the heavier denser plate subjects under the lighter less dense plate
as oceanic crust cools it becomes denser and thicker and gravity forces the lithosphere down into the subduction zone
as it sinks it drags or pulls the plate with it called slab pull
sea floor spreading
paleomagnetism provides evidence that the sae floor has gradually moved apart at a mid ocean ridge
molten rock is forced up forming a new sea floor
hot magma is forced up from the asthenosphere and hardens forming new crust pushing plates apart
paleomagnetism
earths strucrure
the crust
two types of crust
continental - thicker 45-50km and less dense
oceanic - thinner 6-10km denser
moho is the boundary between crust and the mantle
the mantle
layer between the crust and the core and is the widest layer
upper layer
lithosphere - rigid layer above asthenosphere together with the crust
asthenosphere - semi molten plastic type layer moves under high pressure
lower layer
hotter and more dense
the intense pressure at depth keeps the lower mantle solid
the core
inner core
solid centre mostly iron
outer core
semi molten iron and nickel
process impact impact on magnitude
The processes which occur at the plate boundaries impact on the magnitude of the eruption or earthquake
The properties of the magma have a crucial role on the magnitude and frequency of eruptions
properties of magma
intraplate hazards
volcanic hotspots
example- Kilauea, Hawaii 2019
