Formation of the Amazon Basin


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Level 2 Geography - Formation of Amazonia. Takapuna Grammar School

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Formation of the Amazon Basin

  1. 1. Formation of the Amazon Steps of Amazon Formation
  2. 2. Step one
  3. 3. Step one • 500 Million years ago Gondwanaland split up into sections, one of them was the precursor to modern day Africa and South America. This break up occurred due to strong convection currents in the earths mantle. This rock was then subjected to erosion, the eroded material was transported by rivers, in which they accumulated and were compressed under water into sandstone. An inland lake formed which eventually drained into the pacific.
  4. 4. Step Two
  5. 5. Step Two • 90 Million years ago south america and Africa separated from one another. As South America shifted westward it collided with the Nazca plate which was moving east. The collision pushed up the softer sedimentary rock along the western boundary to form fold mountains-the Andes. At the same time land in the north and east buckled, forming a basin.
  6. 6. Step Three
  7. 7. Step Three • 2 Million years ago during the period named the quaternary period the region experienced a cold spell of ice age. This carved up the soft sedimentary rock of the andes and caused much of it to be reduced to sediment. • Freeze thaw action and other denudations processes have kept the height of the Andes to a relatively constant height. • The height of the Andes averages at 4000 m asl
  8. 8. Present Day • Present This sediment was then transported by the many tributaries of the Amazon, such as rio Madeira. IN the upper reaches of the Andes steep gradients mean that river flow is fast and erosion extensive this creates deep v-shaped valleys. As the sediment met the basin in the Andes foothills, river flow was reduced and instead rivers began to deposit their loads.
  9. 9. Present day • Over time the rivers have built up the basin, making it shallower and flatter. Today there is only a 100m drop from the edge of the andes foothills to the amazon mouth. Because of this the basin is liable to flood seasonally, causing the build up of extensive flood plains. Also the river meanders due to small relief, causing widespread deposition across the basin. Sediment tends to originate from the Andes as the rock there is softer than the hard rock of the Guyana and Brazilian plateau’s