hazardous earth

• lithosphere-rigid outer layer of earth composed of the upper mantle and crust
• Asthenosphere- a solid layer of the mantle with a plastic like quality. The high temperature and pressure causes the rock to be viscous and liquid like (ductile)
• Mesosphere- has a 'solid' like rock from the high temperatures and higher pressure
• The mantle- crust boundary is marked by the moho discontinuity

  continental crust depth= 35km

  oceanic crust depth= 10km
• convection currents

  Radioactive decay within the core heats up the layers. Warm plumes of magma are less dense than their surroundings so they rise. When reaching the lithosphere, the magma is forced sideways dragging the lithosphere with it (friction). Once the magma plume cools it descends and the process restarts.
• Ridge push

  newly formed pates at mid ocean ridges are warm, and so they have a higher elevation than the colder denser material further away, gravity causes the other plate at the ridge to push the lithosphere that lies further from the ridge.
• Slab pull

  as the rock gets older it cools and gets denser causing it to lie lower. As they sink in subduction zones they pull the lithosphere with them
• One evidence for continental drift are fossils.

  Fossils of the same fauna/flora have been found on multiple continents despite being separated by ocean, suggesting the continents must of been connected. E.g. Mesosaurus was a fresh water reptile in Africa and Brazil. Tropical fossils have been found in Antarctica (near same tropics)
• Ancient glaciations

  Glacial striations and till deposits have been found South America, Africa from the same time period (unless an ice sheet extended all the way from the south pole to the equator) the continents must have once been connected. Striations show glacial movement away from the equator towards the pole based on current continent locations, suggesting the continents must have been in different locations
• Sea floor spreading and Palaeomagnetism

  Minerals in rocks of different ages align north south or south north. We know the magnetic north and south reverse every 450,000 years.

  when these ocean floor magnetic patterns were mapped they show a zebra like pattern with stripes of reversing polarity. The stripes directly either side of the ridge have modern day polarity.

  This symmetry of polarity suggests the land was created at the same time and they are a similar distance away from the ridge.
• Age of sea floor rocks

  Core drilling has shown that the thickest and oldest sediments are found nearest to the continents away from the ridges, and the youngest are closer to oceanic ridges, plus no older core is older than 200 million years. This suggests land moves from ridges towards continents
• The 'Jigsaw' theory

  At a depth of 1000m below sea level the coasts of south america and africa match exceptionally well. Gaps can be explained by more recent erosion/deposition and isostatic/eustatic change. This suggests that land masses were once connected. Also the mid atlantic ridge follows the shape of the two continents shape.
• Mountain chains and geology

  Eastern South America and West Africa have a continuous ancient rock craton over 2000 million years old stretching between them. Fragments of old fold mountains belt around ~400 million years old are found on widely separated continents today. The uk contains lots of coal deposits however, coal only forms near tropics which suggests the uk must have moved away from the tropics.
• 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
• Stratovolcanoes

  They are composed with layers of ash and acid lava. The acidic magma is highly viscous therefore, it moves slowly and it doesnt travel far before cooling. This gives it its steep cone like shape. They are mainly on convergent plate boundaries and have explosive eruptions which often create chains of stratovolcanoes. Indonesia is the worlds most volcanic country with 130 active along the archipelago.
• 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.
• earthquakes are sudden release of pressure that has built up within the lithosphere sending seismic waves radiating from the focus
• In shallow focus earthquakes the seismic waves dont have to travel too far before reaching the surface therefore they retain more energy
• deep focus earthquakes the seismic waves travel further and therefore the energy dissipates before reaching the surface. Also the deeper the focus the more viscous rock and less energy is released
• 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