ENQ 1

• Top 20 most deadly EQ at destructive place boundaries
• Tambora was a Plinian eruption
• as magnitude increases frequency falls
• the Benioff zone produces strong EQ as lots of tension and friction build
• Shield volcanoes are effusive and erupt basaltic lava which has high viscosity
• Composite volcanoes erupt andesitic or rhyolitic lava which has a high silica content and low viscosity
• EQ eruption in Java 2022 had a low mag at 5.6 but a shallow focal depth at 10km. Damage was exacerbated with poorly built homes that were easily destroyed - 13,000 were displaced
• the nature of the bedrock is an important physical process. Silt and Clay bedrock is likely to become jelly like when shaking occurs due to liquefaction
• P waves travel at 6km/hour and through solids and liquids. They move through a compressing and decompressing system
• s waves travel at 3km/hour. they only travel through solids. they are transverse waves
• L waves are the slowest and most destructive waves. they are confined to the surface but cause crustal fracturing. they move in a rolling motion - much like ocean waves.
• S and P waves are body waves
• L waves are surface waves
• Constructive plate boundaries

  • Two plates pulling away from each other e.g., North America and Eurasian Plate
  • Creates a fault
  • creates shield volcano
  • one plate being pulled in different directions create rift valley
  • rift valley has volcanos e.g., Mt Nyragongo
• Destructive

  • Oceanic - continental
  • Ocean - oceanic
  • the older/ denser plate subducts under the less dense plate
  • subducting plate gets pulled into the mantle due to gravity and partial melting
  • creates a trench e.g., Marianas Trench
  • composite volcanos
  • Benioff Zone
  • Peru-Chile Trench
• conservative/ transform

  • two plates moving in different direction or different speed
  • creates slip and stick behaviour
  • pressure builds
  • released as EQ
  • san andreas fault
• convergent collision

  • continental plates moving toward each other
  • crash - same density
  • fold mountains
  • e.g., Himalayas
• April 2024 - two welsh towns experienced EQ - one had 2.3 mag
• Intraplate EQ - area of existing weakness e.g., past fault line or high levels of pressure that have caused lithosphere to crack - existing faults become re-activated and release seismic waves
• intra-plate volcano - localised area of the lithosphere that is unusually hot - has to do with concentration of radioactive elements and an upwelling of magma from the core - at hotspots magma rises as a plume
• intra-plate volcanos get smaller overtime - crust moving very slowly over hotspot - as move further from mantle plume - eroded etc - becomes smaller as mantle plume is localised
• Fred Wegner - continental drift - plates were moving apart from each other - used to be one large continent called Pangea
• continental drift not accepted by geologists at the time because the theory was weak - Wegner believed that continental crust slid over ocean crust - but the ocean crust was not strong enough to do this
• Plate tectonic theory - explains plate movement with convection currents and slab pull and ridge push
• plate tectonics not well understood - used to think that convection currents main driver but now think it is forcing mechanism of slab pull and ridge push - convection currents seem to weak to drive dense plates
• convection current - there is a heat gradient in the inner workings of the earth - the core is the hottest as radioactive elements decay - hot magma rises because particles become less dense - conducted through the mantle - as rise cool and condense as further from heat source - sink back to the bottom - conveyor belt like effect
• slab pull and ridge push - forcing mechanism - slab pull = chain when falling off table - dense plate that is subducting will 'pull' the rest of this plate with it - ridge push = gravity is pushing plates away from each other - slightly elevated part - called gravitational sliding
• palaeomagnetism shows sea floor spreading - earth changes polarity every 400,000 years - at an ocean constructive margin the plate - new rock formed may have different polarity to the rock most recently formed - magnometers dragged across floor to measure this - seafloor not getting bigger but rock polarity is changing pattern - subduction must be happening - altering bands of rock with different magnetic polarity
• the core is rigid and brittle - oceanic and continental crust - continental is rich in granite and oceanic basaltic
• the mantle - upper mantle - top layer of upper mantle = asthenosphere - rigid because cooler temp and lower pressure - lower mantle = plastic like - separated by the Moho line
• the core - outer core is theorised to be liquid and the inner core is theorised to be solid
• the core is rich in iron and nickel
• the Iceland 2010 eruption caused jokuhlhaup
• jokuhlhaup is a sudden glacier outburst/ flood caused by an subglacial volcanic eruption OR snow and ice melt from the eruption
• Lahar - mud, rock, water combine - mud slides down side of volcano - Mt Merapi
• pyroclastic flow - rolling ball of lava, ash, gas and other tephra - 2000km/hour - Mt. St Helens - can cause asphyxiation - what happened in Pompeii
• ash fall - asphyxiation - weight collapse homes - 100,000 in Pinatubo
• basaltic lava - Hawaii - effusive - low silica content because directly from magma - high gas content - low viscosity - runny
• andesitic - 60% silica content - relatively viscous - can cause pyroclastic flow
• rhyolitic - high viscosity - "great obsidian lake" in Oregon - erupt at 900C - coolest - cause pyroclastic flows - acidic