Volcanism

• what are conglomerates?

  clastic sedimentary rocks that are composed of what was once unconsolidated deposits
• what do conglomerates contain?

  rounded clasts
• what are clasts?

  rocks formed in river environments where deposition occurs
• what is magma?

  molten rock below the earth's surface
• what is lava?

  molten rock at the earth's surface
• what does magma erupt as in effusive eruptions?

  lava flows
• what does magma erupt as in explosive eruptions?

  pyroclastic material
• what are pyroclasts classified by?

  particle diameter
• what is the particle diameter of ash?

  less than 2 mm
• what is the particle diameter of lapilli?

  2 - 64 mm
• what is the particle diameter of volcanic bombs?

  greater than 64 mm
• what are the four things we would expect to find in ash when looking at it under a microscope?

  pumice, lithics, crystals, and glass shards
• what is pumice?

  light coloured vesicular igneous rock formed through the rapid solidification of melt
• what is the vesicular texture in pumice a result of?

  gas trapped in the melt at the time of solidification
• what are lithics?

  rock fragments
• what year did E15 erupt?

  2010
• what were the sequence of events that took place during the E15 eruption?

  flank eruptions took place from the 20th of march until the 12th of April, a couple of days before the explosive eruption on the 14th of April
• what type of eruption was the flank eruption in E15?

  effusive
• what did the effusive flank eruptions during E15 result in?

  lots of lava flows of basaltic composition
• what is a pyroclastic density current?

  a gravity determined flow of hot gases and particles which flow down the flanks of a volcano
• what do pyroclastic density currents produce?

  pyroclastic density current deposits
• what is the common composition of pyroclastic density currents?

  rhyolitic
• what is a lahar?

  the flow of a mixture of water and volcanic material
• what do lahars produce once the flood event has stopped?

  lahar deposits
• what is a debris avalanche?

  landslide down the flanks of a volcano
• what do debris avalanches produce?

  debris avalanche deposits
• what is a phreatic eruption?

  a steam eruption where no deposits are produced
• when do igneous intrusions form?

  when magma cools and solidifies before it reaches the surface
• what are the three common types of intrusions?

  sills, dykes and batholiths
• what are sills?

  when magma intrudes between rock layers, forming horizontal, gently dipping sheets of igneous rocks
• what are dykes?

  formed when magma pushes up towards the surface through cracks in the rock, forming vertical, steeply dipping sheets of igneous rocks
• what are batholiths?

  large deep seated intrusions that form as thick viscous magma slowly makes it way towards the surface - however it rarely gets there
• why is the cooling of magma in solid rock extremely slow?

  because the solid rock that the magma intrudes is a excellent insulator
• what does the extremely slow cooling of magma in solid rock mean that the intrusive igneous rocks are?

  coarse grained (phaneritic)
• what does phaneritic mean?

  igneous rocks with crystals so coarse that they can be viewed by the naked eye
• what are the four ways in which igneous rocks can be classfied?

  chemical composition, crystal/grain size, temperature at which melting starts and viscosity
• what type of materials have the highest viscosity?

  rhyolitic
• what type of materials have the lowest viscosity?

  basaltic
• which types of materials have the middle viscosity - not the least but not the most?

  andesite
• which type of magma tends to have the most explosivity?

  rhyolitic