Internal or Tectonic Forces and Resultant Landforms Past Paper PDF

Internal or Tectonic Forces and Resultant Landforms Start-up question What are the internal forces that affect the formation of landforms? Internal forces are forces that come from the inside of the earth. These forces form the ups and downs on the earth's crust. These forces include folding, faulti...

Internal or Tectonic Forces and Resultant Landforms Start-up question What are the internal forces that affect the formation of landforms? Internal forces are forces that come from the inside of the earth. These forces form the ups and downs on the earth's crust. These forces include folding, faulting, volcanism and earthquakes. Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 3 Social Studies Student Textbook I. Folding 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). A monocline is a type of fold in which all rock layers bend in the same direction. If the layers of rock bend upward, it is called anticline. If the layers of rock bend downward, it is called syncline. Fold Mountains Start-up questions What are Fold Mountains? List the major Fold Mountains of the world. Fold Mountains are formed by crust which has been uplifted, and folded by compressional forces. Fold mountains are usually formed from sedimentary rocks and are usually found along the edges of continents. This is because the thickest deposits of sedimentary rock are generally accumulated along the edges of continents. The following are major Fold Mountains of the world: 1. Andes (South America) 2. Rockies (North America) 3. Alps (Europe) 4. Himalayas (Asia) 5. Atlas (North Africa) 6. Cape Ranges (South Africa) 7. Australian Alps (Australia) Figure 1.2 Major Fold Mountains of the world Figure 1.1 Anticline and syncline Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 4 Social Studies Student Textbook II. Faulting Start-up questions What is faulting? Describe the major features formed by faulting. Movements in the crust of the earth sometimes make cracks. These cracks are called faults. Faults occur due to two basic forces. These are tensional and compressional forces. Tension force causes a normal fault, and compressional force causes a reverse fault. Figure 1.3 Normal and reverse fault Rift valleys and block/Horst/ mountains are major features formed by faulting. Figure1.4 Rift valley and Block Mountain Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 5 Social Studies Student Textbook Rift Valleys Start-up questions What is rift valley? How is it formed? 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. It 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. Figure 1. 5 The Great East African Rift Valley The Ethiopian Rift Valley is part of the East African Rift Valley. It extends from northeast to south west. Features found in the Rift Valley include active volcanoes, lakes, hot springs and fumaroles. Block (Horst) Mountains Start-up questions What is Block Mountain? How is it formed? Block Mountains are formed by the uplift of land between two parallel faults. These mountains are found closer to fold mountains in many parts of the world. Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 6 Social Studies Student Textbook III. Volcanism Start-up questions What is volcanism? What are the landforms formed by volcanism? Volcanism is the process by which molten rock (magma) is forced out to the surface of the earth. The high temperature inside the earth changes rocks into molten magma. 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 hole or 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 deffrent types of landforms. These are: A. 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. Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 7 Social Studies Student Textbook Figure 1.6 Major volcanic features Types of volcanoes Volcanoes have three types. These are: 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 Effects of volcanism on human life Volcanic eruption has both negative and positive impacts on human life. Let us look at these impacts as follows:- i. Advantages of volcanic eruption Volcanic eruption has the following advantages. It: \" 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, etc. Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 8 Social Studies Student Textbook ii. Disadvantages of volcanic eruption Volcanoes emit hot, dangerous gases, ash, lava, and rock that are powerfully destructive. Volcanic eruptions can result in additional threats to health, such as floods, mudslides, power outages, drinking water contamination and wildfires. It also results in infectious disease, respiratory illness, burns, injuries from falls, and vehicle accidents related to the slippery, hazy conditions caused by ash. IV. Earthquake Start-up questions What is an earthquake? Where do earthquakes frequently occur? Earthquakes are sudden movements in the earth's crust. They are caused by internal movements deep down inside the earth. Earthquakes are frequently associated with faults. They take place along fault lines where the earth's crust is weak. When an earthquake occurs, vibrations from the centre spread out in the form of waves in all directions. The point at which an earthquake originates is called the focus. The point on the earth's surface immediately above the focus is called the epicenter. The intensity of an earthquake is measured by an instrument called a seismometer, and it is recorded on a seismograph. The scale which gives the magnitude is called the Richter scale. It ranges from 0 to 9. The recordes that range to 5 indicate minor or light; if it is 5 to 7 moderate to strong. If the range is 7 to 8, it is an indication of major earthquake and if it ranges above 8 or more, it is considerd as a great one. The Ring of Fetena.net : Ethiopian No\#1 Educational Resource GRADE 8 9 Social Studies Student Textbook Fire, also referred to as the Circum-Pacific Belt, is a path along the Pacific Ocean characterized by active volcanoes and frequent earthquakes. The majority of Earth's volcanoes (75%) and earthquakes (90%) take place along the Ring of Fire. Effects of Earthquakes Loss of life and destruction of property Displacement of parts of the earth's crust vertically or laterally Landslides and deep cracks in surface rocks The devastation of cities, fires and diseases The rise or lowering of the sea floor