Unit one

• Internal forces are forces that come from the inside of the earth. These forces form the ups and downs on the earth’s crust.
• Internal forces include folding, faulting, volcanism and earthquakes.
• Folding is the bending of rock layers due to earth movements from one or two sides.
• Folds are most visible in rocks that contain layering (sedimentary rocks).
• If the layers of rock bend upward, it is called anticline.
• If the layers of rock bend upward, it is called anticline.
• If the layers of rock bend downward, it is called syncline.
• Fold Mountains are formed by crust which has been uplifted, and folded by compressional forces.
• Fold mountains

  Andes=South America

  Rockies=North America

  Alps=Europe

  Himalayas=Asia

  Atlas=North Africa

  Cape Ranges=South Africa

  Australian Alps=Australia
• Movements in the crust of the earth sometimes make cracks. These cracks are called faults.
• Faults occur due to two basic forces: Tensional and compressional forces.
• Tension force causes a normal fault,

  Compressional force causes a reverse fault.
• Rift valleys and block(Horst) mountains are major features formed by faulting.
• A rift valley is formed when the land between two parallel faults sinks down
• The largest rift valley in the world is the East African Rift Valley.
• East African Rift Valley extends 7200 km from Syria to Mozambique, passing through the Red Sea; it touches Eritrea, Ethiopia, Kenya, Tanzania, Democratic Republic of Congo (DRC), Rwanda and Burundi. It covers 5600 km in Africa.
• Block Mountains are formed by the uplift of land between two parallel faults.
• Volcanism is the process by which molten rock (magma) is forced out to the surface of the earth
• The magma that reaches the surface is called lava.
• The lava may come out on the surface through a single hole called a vent or several cracks called fissures.
• When a hole is formed at the top of the cone of a volcano it is called crater.
• If the crater is very wide, it is known as caldera.
• A lake formed in a caldera is known as Crater Lake. Mount Zequala is a very good example of cone-shaped volcanic mountain with a crater lake.
• Volcanic activities may result in two different types of landforms. These are:

  1. Extrusive landforms
  2. Intrusive landforms
• 1. Extrusive landforms: form on the surface of the earth. They include volcano, crater, caldera and lava.
• B. Intrusive landforms: result from solidified magma before reaching the surface of the earth. When magma collects in the crust, it forms batholiths, laccoliths, dykes and sills.
• Batholith: is a very large mass of magma which accumulates in the crust.
• Laccolith: is a mushroom shaped body of intrusive igneous rock smaller than a batholith
• Dyke: is formed when magma solidifies in a vertical or near-vertical crack.
• Sill: is a near horizontal intrusion of igneous rock between two rock layers.
• Volcanoes have three types. These are:

  i. Active volcanoes

  ii. Dormant volcanoes

  iii. Extinct volcanoes
• i. Active volcanoes:- these types of volcanoes have a recent history of eruptions; they are likely to erupt again. Example: Erta'li, Fentale Dubbi and Damailai.
• ii. Dormant volcanoes:- they have not erupted for a very long time, but they may erupt at a future time. Example: Tatali, and Dabbahu
• iii. Extinct volcanoes:- they are dead volcanoes that are not expected to erupt in the future. Example: Mt Ras Dejen, Mt Batu, Mt Zuquala etc
• Advantages of volcanic eruption

  Provides hot water for bathing

  Helps to generate geothermal energy

  Provides fertile soils that is good for farming

  Creates dramatic scenery that can attract tourists

  Forms hard and expensive minerals used as jewelry

  Provides hard rocks for building
• Disadvantages of volcanic eruption

  • emit hot, dangerous gases, ash, lava, and rock that are powerfully destructive
  • result in additional threats to health, such as floods, mudslides, power outages, drinking water contamination and wildfires
  • o results in infectious disease, respiratory illness, burns, injuries from falls, and vehicle accidents related to the slippery, hazy conditions caused by ash.
• Earthquakes are sudden movements in the earth’s crust.
• Earthquakes are caused by internal movements deep down inside the earth.
• Earthquakes are frequently associated with faults.
• The point at which an earthquake originates is called the focus.