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TECTONIC PROCESSES AND HAZARDS 1.3.1 - Coggle Diagram
TECTONIC PROCESSES AND HAZARDS
1.3.1
CHARACTERISTICS OF EARTH'S STRUCTURE
CORE
iron and nickle
inner core = solid, outer core = semi-molten
MANTLE
semi-molten
asthenosphere = upper part
84% of earths volume
up to 4000 degrees
CRUST
outer layer
oceanic + continental
oceanic = thinner (6-10km) - made of sima
continental = thicker (70km) - made of sial
LITHOSPHERE
outer layer
crust and outermost layer of upper mantle
MECHANISMS OF PLATE MOVEMENT
CONVECTION CURRENTS
heat from core moved to surface by convection
hot magma rises as it becomes less dense
becomes more dense at the top as it cools and sinks - carries the plates with it
plates move on the asthenosphere
RIDGE PUSH
magma rises at divergent boundary
ocean ridge is present
rising magma material creates the potential for plates to move away from the ridge
because mid-ocean ridges are higher in elevation, gravity pulls the surrounding rocks down and away from the ridge
SLAB-PULL
convergent plate boundaries
denser plate subducts
subducting plate = colder and heavier than mantle so it sinks, pulling the rest of the plate with it
MAJOR DRIVING FORCE BEHIND TECTONIC PLATE MOVEMENT
PLATE MARGINS
DIVERGING
x2 oceanic
magma rises between gap, forms new land
ocean ridge
example: Mid-Atlantic Ridge
volcanoes rise above sea level creating islands
x2 continental
hot magma forces crust to bulge - mountain ridges
crust fractures - parallel faults - example: East African Rift Valley
volcanic activity: Mount Kilimanjaro
CONVERGING
2x oceanic
denser plate subducts
ocean trench - example: Mariana Trench, South Pacific Ocean
subducted plate heated and melts
some may rise creasing an island arc - example: Tonga Islands
oceanic and continental
denser = subducted by slab pull
less dense (continental) buckles, creating mountains
oceanic melts, creating magma chamber, rises through weaknesses creating a volcano
subduction zone can cause earthquakes due to friction in the Benioff Zone
example: Cascade Range, North America
TRANSFORM
2 plates slide past eachother
no subduction and no volcanic activity
earthquakes occur due to build up of pressure suddenly released
example: San Andreas Fault, California - Pacific Plate and North American Plate
HOT SPOTS
small areas away from plate margins with unusually high heat flow
plume of magma rises from asthenosphere - pushed through crust creating volcanoes
as plate moves, a line of volcanoes is created
oceanic hotspots cool, creating islands: Hawaii
continental become extinct: Yellowstone, USA
ALTERNATIVE
plates have weaknesses as they are stretched by slab pull, so molten rock moves to the surface through these weaknesses
DISTRIBUTION OF TECTONIC HAZARDS
EARTHQUAKES
along plate margins
diverging - shallow and comes with volcanic activity
oceanic crust subduction - powerful, creates tsunamis
converging continental - shallow and can be powerful and hazardous if humans in the area
human activity - minor earthquakes
VOLCANOES
along plate margins
divergent - mid ocean ridges, non violent as underwater
convergent - can be violent and hazardous, example: Mt St Helens, Cascade Range, USA
hotspots - less violent, more lava, cause lots of damage - example: Hawaii, 2018
PHYSICAL HAZARD PROFILES
MAGNITUDE
describes size/physical force
VOLCANOES - VEI=0-8 - volume of material erupted, cloud height, gentle to mega colossal - sulfur dioxide not taken into account
EARTHQUAKES - richter scale 1-9
PREDICABILITY
many are unpredictable, can influence impact
can predict location but not time
an accurate prediction = less impact
VOLCANOES
easier to predict as there are warning signs
can monitor changes: gas, temp, ground deformation
cant predict exactly when or how large
EARTHQUAKES
cant predict, no pattern, no reliable indicator
FREQUENCY
frequent = smaller magnitude, less impact
less frequent = larger magnitude, more impact
areas with frequent earthquake have measures - earthquake resistant buildings, evacuation plans - example: JAPAN
DURATION
longer duration = more impact
more secondary hazards - example: Phillipines, 1991, long duration, high impact
SPEED OF ONSET
how quickly the peak of event arrives
AREAL EXTENT
size of geographical area affected by the event