section_path: Geology
section_name: Geology
paragraph_text: Geology
  
  Geologically, Lake Victoria is relatively young at about 400,000 years old. It was formed when westward-flowing rivers were dammed by an upthrown crustal block. During the Miocene era, what is now the catchment area of the lake was on the western side of an uplifted area that functioned as a continental divide, with streams on the western side flowing into the Congo River basin and streams on the eastern side flowing to the Indian Ocean. As the East African Rift System formed, the eastern wall of the Albertine Rift (or Western Rift) rose, gradually reversing the drainage towards what is now Lake Victoria. The opening of the main East African Rift and the Albertine Rift downwarped the area between them as the rift walls rose, creating the current Lake Victoria basin.
  
  During its geological history, Lake Victoria went through changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes. Geological cores taken from its bottom show Lake Victoria has dried up completely at least three times since it formed. These drying cycles are probably related to past ice ages, which were times when precipitation declined globally. Lake Victoria last dried out about 17,300 years ago, and it refilled 14,700 years ago as the African humid period began.