volcanoes

• Explosive volcanos=

  Pressure builds up causes explosive eruptions

  They happen at convergent plate boundaries

  Have acidic lava thats more thicker ( viscous)

  Erupts any material

  Often have long periods with no activity

  They have steep sided stratovolcanoes, calderas, composite
• Effusive volcanoes=

  Free flowing basic lava creates non violent eruptions

  Divergent plate boundary

  Low viscous basic lava

  Limited explosive force as gas bubbles expand freely

  They erupt gas and lava

  More frequent eruptions that can last months

  gently sloping sides, shield shape, lava plateaux
• Calderas are craters and an explosive volcanic feature. Acidic magma is highly viscous and therefore moves slowly allowing vents to be plugged. This prevents the magma rising so pressure is built up. When the pressure exceeds the force of the solidified magma, the volcano erupts explosively sometimes blowing the top part off. Calderas are 2km in diameter. They occur when the magma chamber is emptied after an eruption, which leaves the top unsupported and therefore collapses. It can often fill with water to form a lake.
• Sills are mainly explosive and are formed when Lava which mainly flows between beds of rock can cool to create new igneous layers. Sills are fed by dykes. The rock must have pre existing fractures/ weak connections between planes or else it must be brittle enough to create new gabs.
• Dykes are formed when magma intrudes into a crack then crystallises as a sheet intrusion, either cutting across layers of rock or through contiguous mass of rock. Tectonic deformation may rotate the dyke and its surrounding strata so that dyke becomes horizontal.
• Batholiths are very large intrusive masses of magma covering 40 square miles. They form either aggregation of dykes/sills and, less dense magma parcels rise through brittle rocks. but cool and solidify before they reach the surface. If it is less than 40 square miles then its a stock.
• Lava plateaux are an effusive feature. A flood basalt is the result of a giant volcanic eruption or a series of eruptions through several vents that stretches over land/ ocean floor with basalt lava. The lava must have low viscosity and erupts effusively. Multiple and extensive lava flows cover the original landscape to eventually form a plateaux.
• shield volcanoes are an effusive feature. They are short and wide volcanoes made from layers of lava flows at divergent plate boundaries. It requires effusive eruptions as they are not viscous so the lava travels further before setting. Successive eruptions build up layers and can result in the volcanoes extending horizontally for 10 of km. These are mainly on ocean floors, hotspots and in Iceland.
• Hotspots is a region where rising mantle plume is significantly hotter than the surrounding mantle, causing it to break through the crust as a volcano. The location of the mantle plume is fixed but the crust is continuously moving over it. This causes the mantle plume to puncture the surface at intervals creating chains of dormant volcanoes with an active volcano at one end.
• Super volcanoes is when a volcano erupts with a magnitude of 8 VEI and ejects over 1000km squared of tephra. The impact of these very high magnitude events us deduced from the extent and the depth of their ash layers and their impact on plants and animal species.
• lava flows are streams of molten rock that pour from an erupting vent and can reach up to 40mph.
• pyroclastic flows are fast moving currents of hot gas and volcanic matter that reach up to 1000 degrees Celsius and speeds up to 70 km/h.
• tephra is fragmented material produced by a volcanic eruption. The speed would be relevant to the power and force of the eruption.
• volcanic gas happens when magma rises towards the surface and the pressure decreases, so the gas is released from the liquid portion of the magma and continues to travel upward. Eventually this gets released into the atmosphere. Large eruptions release large amounts of gas in a short time.
• landslides happen when gravity driven rock slides down. This can occur at times as a result of heavy rainfall and earthquakes.
• Lahars are volcanic ash mixing with water to form dense slurry similar to freshly mixed concrete.
• Tsunamis are generated by explosive eruptions on volcanic islands or by submarine caldera collapse which is underwater.
• vulcanian eruptions

  Powerful gas explosions

  caused by volcanic plug

  produce more tephra

  Andesitic viscous lava
• Icelandic eruptions

  Persistent fissure eruption

  large quantities of basaltic lava

  Lava is very runny

  Creates lava plateaux/flood basalts
• hawaiian eruptions

  Central activity as opposed to a fissure

  Fissures may radiate out from a central zone

  Runny, basaltic lava

  gases escape easily and occasional pyroclastic activity
• strombolian eruption

  • Frequent explosive gas eruption
  • Usually a viscous form of basaltic lava
  • Pyroclastic flow
  • least viscous
• pelean eruption

  • Explosive outbursts
  • Pyroclastic flows and other hazards
• Plinian eruptions

  • violent gas explosions with enormous gas/debris cloud
  • cloud is so large it can cause lightning
  • part of the volcano might be blasted away