volcanoes

• Phreatic eruptions don't require a lot of water – if groundwater or snow/ice melt seeps into a volcanic edifice and heats up (typically due to a new intrusion of magma coming into the upper part of the volcano), that water can flash to steam causing an explosion.
• Phreatomagmatic eruptions require more water than phreatic. What happens in a phreatomagmatic eruption is usually the erupting magma is directly introduced into a body of water – possibly a crater lake, meltwater from snow or ice, seawater – and the very large contrast in heat (sometimes upwards of 1100°C between water and basalt) causes an explosion of both the water and magma.
• 2010 eruption at Eyjafjallajökull in Iceland was initially a phreatomagmatic eruption when the explosive phase started – the erupting magma came into contact with the melting icecap on the volcano
• crust lithosphere:

  • thin as a skin of apple
  • oceanic crust (sima) layer consisting of basalt avergaing 6-10km thick deepest 1200 temp
  • continental crust (sial) up to 70km thick. crust seperated from mantle by mono discontinuity. crust and rigid layer of the mantle collectively known as lithosphere
• mantle:

  • composed mainly of silicate rocks rich in iron and magnesium
  • apart from rigid layer rocks in the remainder (asthenosphere)are in semi-molten mantle extends to depth of 2900km 5000 temp
  • increased temp to generate convection current
• core:

  • consists of nickel and iron
  • size of mars
  • outer core semi-molten
  • inner core solid
  • temperature at centre of earth (6371 km) is 6200 temp hotter than the surface of the sun
• oceanic crusts underly oceanic basins and primarily made of basalt
• continental crust underly continents and composed of granite low density so float high relief
• rocks in upper mantle are brittle and cool break under stress like earthquake
• rocks in lower mantle are hot and soft but not mantle flow when subjected to forces no breaking
• converging plates move towards each other e.g west coast of south america
• diverging/ constructive plates is when the plates move away from each other e.g iceland
• conservative boundary is when plates move along side each other in opposite directions or same direction at different speeds such as the san andreas fault
• internal heating and mantle convection currents:

  heat from the core is moved towards surface by convection currents in mantle . spreads out the surface carrying plates with them
• slab pull:

  convergent boundary one plate is denser and heavier. denser plate subducts beneath less dense. subducting plate is colder and heavier than mantle so continues to sink pulling the rest of the plate with it
• ridge push is when molten magma rises to the mid ocean ridge at divergent boundary . rocks in the lithosphere are heated and expand so they rise above seafloor forming slope away from the ridge as the rock cools it becomes denser and gravity causes slide down ridge exerting force on plates resulting in gravitational sliding which is an active driving force
• caldera volcano:

  • gasses trapped in magma chamber and cause explosive increasing explosivity of eruption
  • upper part of volcano can be destroyed
  • ground above magma can be subsided leaving a large depression resulting in a flood
  • yellow stone usa
• cinder/ ash volcano:

  • gas forces lava high into the air where it breaks into small fragments
  • fragment coll form cinder
  • produces short symmetrical cone steep sides and caldera at top
  • often occur on side of shield composite volcano
  • formed after one eruption
  • particun mexico
• acid volcano:

  • viscous acid lava effusive eruption cannot flow before solidifying
  • lava builds up steep side cone
• composite stratovolcano:

  • many layers of solidified lava and volcanic ash from different eruptions
  • lava slow flow solidifies quick
  • steep sloped sides
  • ash explosive eruptions often after blocked vent with solidified lava
  • converging plate boundary
  • mt fuji japan
• shield volcano

  • effusive eruption high quantity of lava from centeral vent
  • lava travels long distance
  • produce tall volcano and gentle sloped sides
  • eruptions frequent and explsive
  • diverging plate boundary and hotspots
  • mauna loa hawaii
• pyroclastic flow:

  high density mix of hot volcanic gas, volcanic fragments such as pumice and ash moves at high speeds down slope

  eruption column collapses during explosive eruption and material is ejected into the atmosphere

  lava boils over the vent. material emitted during explosive eruption and travels rapidly downslope

  collapse lava dome steep slope collapse due to gravity

  1000 temp
• lava flows

  streams of molten rock pouring from erupting vent. speed of travel depends on the viscosity of the lava. is the least hazardous destroy infastructure
• ash falls

  tephra emitted during explosive eruption inc ash and pulverised rock and volcanic glass

  huge quantities over large area as a result of wind

  5% volcano death respiratory issues
• lahars

  mixture of ash and debris and water travels down slope usually valley

  water can come from snow or ice
• toxic gases

  magma rises to the surface the pressure drops and gases are released and reach atmosphere e.g water vapour, co2, and sulfuric acid can cause respiratory issues
• volcanic landslides

  mass of volcanic rocks and debris that move rapidly under the force of gravity
• jo kulhlaups

  glacial outburst of flood

  sub glacial volcanic activity can cause melting of the overlying glacier

  trapped meltwater is released from dam causing a brief but significant flood

  usually occurs in sparsley populated areas