geography

• seafloor spreading: magma rises from mantle to ocean floor

  eg. mid atlantic
• underwater divergent –> crack in seafloor –> underwater volcano
• continental plate is *LESS DENSE* than oceanic plate
• magma: molten mantle
• mantle: mostly solid rock, 1000-3700°C, 2900km thick
• core: 4400-6000°C, 3300km
• crust: lowest temperature, 6-70km thick
• seafloor divergence –> magma released –> cools –> new seafloor
• continental plate divergence: break up of continents eg. Great Rift Valley
• • low land, steep sides, flat valley floor
  • formed by Somalian boundary of the African plate moving away from Nubia plate boundary of African plate
  • 6000km long
  • 30-100km wide
  • active volcano, earthquake fractures –> tectonic activity evidence
• India plate converges into Eurasian plate at a fast pace which causes tall mountains
• plate: broken pieces of lithosphere

  types of plate boundaries: divergent (move away), convergent (move towards), transform (move past)
• earthquakes are vibration due to sudden release of stored energy which causes fault lines
• magnitude is amount of seismic energy released

  measured by seismometer, on Ritcher scale

  1.0(usually not felt)—>9.0(destruction on impact)

  >6.0 usually appear on the news
• moment magnitude scale – give total energy released afterwards

  earthquake causes extent of damage, may vary based on other factors: – population density – higher PD, more fatal
• factors of earthquake:

  • Time of occurrence (at night, people are asleep)
  • level of preparedness (drills, earthquake resistant buildings rescue workers)
  • distance from epicentre (closer to epicentre, more severe)
  • type of soil (loose soil amplify seismic waves)
• volcano is a landform formed by magma

  vulcanicity –> upward movement of the magma into the crust and onto the surface
• not all volcanoes/ mountains are volcanoes/ mountains
• volcanoes: magma is molten rock found under the surface ——————————————————————————parts: magma chamber, cone, vents(opening), crater, caldera(if any)

  ————————————————————————————crater is perimeter of opening

  caldera is when the crater collapses and become shorter than before

  magma ejected onto the surface is lava
• lava flow: cools when in contact with ground, air or water

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  lava flow on ground is relatively slow
• pyroclastic flow:

  • hot cloud of gas, ash and rocks travelling at great speeds down the slopes
  • occurs when column of hot air and gas is thrown into the air and falls back down
  • typically travels several kilometres
  • up to 700°C